Nonlinearly-enhanced energy transport in many dimensional quantum chaos
Brambila, D. S.
2013-08-05
By employing a nonlinear quantum kicked rotor model, we investigate the transport of energy in multidimensional quantum chaos. This problem has profound implications in many fields of science ranging from Anderson localization to time reversal of classical and quantum waves. We begin our analysis with a series of parallel numerical simulations, whose results show an unexpected and anomalous behavior. We tackle the problem by a fully analytical approach characterized by Lie groups and solitons theory, demonstrating the existence of a universal, nonlinearly-enhanced diffusion of the energy in the system, which is entirely sustained by soliton waves. Numerical simulations, performed with different models, show a perfect agreement with universal predictions. A realistic experiment is discussed in two dimensional dipolar Bose-Einstein-Condensates (BEC). Besides the obvious implications at the fundamental level, our results show that solitons can form the building block for the realization of new systems for the enhanced transport of matter.
Laane, Colja; Ford, William E.; Otvos, John W.; Calvin, Melvin
1981-01-01
The photosensitized reduction of heptylviologen in the bulk aqueous phase of phosphatidylcholine vesicles containing EDTA inside and a membrane-bound tris(2,2′-bipyridine)ruthenium(2+) derivative is enhanced by a factor of 6.5 by the addition of valinomycin in the presence of K+. A 3-fold stimulation by gramicidin and carbonyl cyanide m-chlorophenylhydrazone is observed. The results suggest that, under these conditions, the rate of photoinduced electron transfer across vesicle walls in the absence of ion carriers is limited by cotransport of cations. The rate of electron transfer across vesicle walls could be influenced further by generating transmembrane potentials with K+ gradients in the presence of valinomycin. When vesicles are made with transmembrane potentials, interior more negative, the quantum yield of heptylviologen reduction is doubled, and, conversely, when vesicles are made with transmembrane potentials, interior more positive, the quantum yield is decreased and approaches the value found in the absence of valinomycin. PMID:16593002
Quantum Transport in Mesoscopic Systems
Indian Academy of Sciences (India)
988. RESONANCE │ November 2010. GENERAL │ ARTICLE. Quantum Transport in Mesoscopic Systems. CoulombBlockadeandKondoEffect. Navinder Singh. Keywords. Quantum transport, mesoscopic systems, Coulomb blockade,. Kondo effect. Navinder Singh works in the Physical Research. Laboratory, Ahmedabad.
Indian Academy of Sciences (India)
Transport in quantum wires. SIDDHARTHA LAL, SUMATHI RAO£ and DIPTIMAN SEN. Centre for Theoretical Studies, Indian Institute of Science, Bangalore 560 012, India. £ Harish-chandra Research Institute, Chhatnag Road, Jhusi, Allahabad 211 019, India. Abstract. With a brief introduction to one-dimensional channels ...
International Nuclear Information System (INIS)
Deus, Fernanda; Continetino, Mucio
2011-01-01
Full text. In this work we study the time dependent transport in interacting quantum dot. This is a zero-dimensional nano structure system which has quantized electronic states. In our purpose, we are interested in studying such system in a Coulomb blockade regime where a mean-field treatment of the electronic correlations are appropriate. The quantum dot is described by an Anderson type of Hamiltonian where the hybridization term arises from the contact with the leads. We consider a time dependence of both the energy of the localized state in the quantum dot and of the hybridization-like term. These time dependent parameters, under certain conditions, induce a current in the quantum dot even in the absence of difference on the chemical potential of the leads. The approach to this non-equilibrium problem requires the use of a Keldysh formalism. We calculate the non- equilibrium Green's functions and obtain results for the average (equilibrium term) and the non-equilibrium values of the electronic occupation number in the dot. we consider the possibility of a magnetic solution, with different values for the average up and down spins in the quantum dot. Our results allow to obtain, for instance, the tunneling current through the dot. The magnetic nature of the dot, for a certain range of parameters should give rise also to an induced spin current through the dot
Quantum Transport in Mesoscopic Systems
Indian Academy of Sciences (India)
A short introduction to the quantum transport in mesoscopic systems is given, and various regim- es of quantum transport such as diffusive, ballis- tic, and adiabatic are explained. The effect of interactions and inelastic scattering along with the characteristic coherent effects of mesoscopic systems give interesting new ...
Stochastic Energetics of Quantum Transport
Ghosh, Pulak Kumar; Ray, Deb Shankar
2006-01-01
We examine the stochastic energetics of directed quantum transport due to rectification of non-equilibrium thermal fluctuations. We calculate the quantum efficiency of a ratchet device both in presence and absence of an external load to characterize two quantifiers of efficiency. It has been shown that the quantum current as well as efficiency in absence of load (Stokes efficiency) is higher as compared to classical current and efficiency, respectively, at low temperature. The conventional ef...
Thermoelectric transport through quantum dots
Energy Technology Data Exchange (ETDEWEB)
Merker, Lukas Heinrich
2016-06-30
In this thesis the thermoelectric properties (electrical conductance, Seebeck coefficient and thermal conductance)of quantum dots described by the Anderson impurity model have been investigated by using the numerical renormalization group (NRG) method. In order to make accurate calculations for thermoelectric properties of quantum impurity systems, a number of recent developments and refinements of the NRG have been implemented. These include the z-averaging and Campo discretization scheme, which enable the evaluation of physical quantities on an arbitrary temperature grid and at large discretization parameter Λ and the full density matrix (FDM) approach, which allows a more accurate calculation of spectral functions and transport coefficients. The implementation of the z-averaging and Campo discretization scheme has been tested within a new method for specific heats of quantum impurities. The accuracy of this new method was established by comparison with the numerical solution of the Bethe-ansatz equations for the Anderson model. The FDM approach was implemented and tested within a new approach to the calculation of impurity contributions to the uniform susceptibilities. Within this method a non-negligible contribution from the ''environmental'' degrees of freedom needs to be taken into account to recover the correct susceptibility, as shown by comparison with the Bethe-ansatz approach. An accurate method to calculate the conductance of a quantum dot is implemented, enabling the extraction of the Fermi liquid scaling coefficients c{sub T} and c{sub B} to high accuracy, being able to verify the results of the renormalized super perturbation theory approach (within its regime of validity). The method was generalized to higher order moments of the local level spectral function. This, as well as reduction of the SU(2) code to the U(1) symmetry, enabled the investigation of the effect of a magnetic field on the thermoelectric properties of quantum
Quantum Transport in Mesoscopic Systems
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 15; Issue 11. Quantum Transport in Mesoscopic Systems - Coulomb Blockade and Kondo Effect ... Author Affiliations. Navinder Singh1. Room No 457 Theoretical Physics Division Physical Research Laboratory Navrangpura Ahmedabad 380 009 ...
Quantum enhanced optical sensing
DEFF Research Database (Denmark)
Schäfermeier, Clemens
The work in this thesis is embedded in the framework of quantum metrology and explores quantum effects in solid state emitters and optical sensing. Specifically, the thesis comprises studies on silicon vacancy centres in nanodiamonds, phase measurements and cavity optomechanics utilising optical...... squeezed states, and a theoretical study on quantum amplifiers. Due to its similarity to single atoms, colour centres in diamond are ideal objects for exploring and exploiting quantum effects, because they are comparably easy to produce, probe and maintain. While nitrogen vacancy centres are the most...... identified spectral diffusion as the main hindrance in extending spin coherence times. Overcoming this issue will provide a promising candidate as an emitter for quantum information. Next, the question of how squeezed states of light can improve optical sensing was addressed. For this purpose, a squeezed...
Quantum transport in semiconductor nanostructures
Energy Technology Data Exchange (ETDEWEB)
Kubis, Tillmann Christoph
2009-11-15
The main objective of this thesis is to theoretically predict the stationary charge and spin transport in mesoscopic semiconductor quantum devices in the presence of phonons and device imperfections. It is well known that the nonequilibrium Green's function method (NEGF) is a very general and all-inclusive scheme for the description of exactly this kind of transport problem. Although the NEGF formalism has been derived in the 1960's, textbooks about this formalism are still rare to find. Therefore, we introduce the NEGF formalism, its fundamental equations and approximations in the first part of this thesis. Thereby, we extract ideas of several seminal contributions on NEGF in literature and augment this by some minor derivations that are hard to find. Although the NEGF method has often been numerically implemented on transport problems, all current work in literature is based on a significant number of approximations with often unknown influence on the results and unknown validity limits. Therefore, we avoid most of the common approximations and implement in the second part of this thesis the NEGF formalism as exact as numerically feasible. For this purpose, we derive several new scattering self-energies and introduce new self-adaptive discretizations for the Green's functions and self-energies. The most important improvements of our NEGF implementation, however, affect the momentum and energy conservation during incoherent scattering, the Pauli blocking, the current conservation within and beyond the device and the reflectionless propagation through open device boundaries. Our uncommonly accurate implementation of the NEGF method allows us to analyze and assess most of the common approximations and to unveil numerical artifacts that have plagued previous approximate implementations in literature. Furthermore, we apply our numerical implementation of the NEGF method on the stationary electron transport in THz quantum cascade lasers (QCLs) and answer
Tang, Xin; Wu, Guang Fu; Lai, King Wai Chiu
2017-06-01
We report a strategy to realize and facilitate the photocarrier transport from mercury selenium colloidal quantum dots (HgSe CQDs) into silicon with the assistance of twisted graphene. A nanocomposite material consisting of HgSe CQDs and twisted graphene has been synthesized. By bringing the nanocomposites into contact with silicon, a HgSe CQD-twisted graphene nanocomposite/silicon junction was fabricated and demonstrated photoresponses in the long-wave infrared range. In the nanocomposites, the surface of twisted graphene was decorated with HgSe CQDs. Benefiting from the twisted structure in the nanocomposites, the active sensing area and light-matter interaction length are greatly increased. Driven by the interfacial built-in potential, photocarriers directly transfer from HgSe CQDs into the twist graphene, which serves as a fast carrier transport pathway to silicon, leading to high photocarrier collection efficiency. Compared with vertically stacked HgSe CQD film/flat graphene, the application of HgSe CQD-twisted graphene nanocomposites avoids photocarriers transporting via the hopping mechanism and over 2700% enhancement ratio of spectral responsivity was achieved, reaching 31.5 mA/W@9 μm. The interfacial energy band diagram was deduced for a better understanding of the photocarrier transfer process occurring at the interface between HgSe colloidal quantum dots, twist graphene, and silicon.
Quantum transport and electroweak baryogenesis
Energy Technology Data Exchange (ETDEWEB)
Konstandin, Thomas
2013-02-15
We review the mechanism of electroweak baryogenesis. The main focus of the review lies on the development of quantum transport equations from first principles in the Kadanoff-Baym framework. We emphasize the importance of the semi-classical force that leads to reliable predictions in most cases. Besides, we discuss the status of electroweak baryogenesis in the light of recent electric dipole moment probes and collider experiments in a variety of models.
Quantum transport in carbon nanotubes
DEFF Research Database (Denmark)
Laird, Edward A.; Kuemmeth, Ferdinand; Steele, Gary A.
2015-01-01
Carbon nanotubes are a versatile material in which many aspects of condensed matter physics come together. Recent discoveries, enabled by sophisticated fabrication, have uncovered new phenomena that completely change our understanding of transport in these devices, especially the role of the spin...... blockade. This can be exploited to read out spin and valley qubits, and to measure the decay of these states through coupling to nuclear spins and phonons. A second unique property of carbon nanotubes is that the combination of valley freedom and electron-electron interactions in one dimension strongly...... and valley degrees of freedom. This review describes the modern understanding of transport through nanotube devices. Unlike conventional semiconductors, electrons in nanotubes have two angular momentum quantum numbers, arising from spin and from valley freedom. We focus on the interplay between the two...
Electron transport in quantum dots
2003-01-01
When I was contacted by Kluwer Academic Publishers in the Fall of 200 I, inviting me to edit a volume of papers on the issue of electron transport in quantum dots, I was excited by what I saw as an ideal opportunity to provide an overview of a field of research that has made significant contributions in recent years, both to our understanding of fundamental physics, and to the development of novel nanoelectronic technologies. The need for such a volume seemed to be made more pressing by the fact that few comprehensive reviews of this topic have appeared in the literature, in spite of the vast activity in this area over the course of the last decade or so. With this motivation, I set out to try to compile a volume that would fairly reflect the wide range of opinions that has emerged in the study of electron transport in quantum dots. Indeed, there has been no effort on my part to ensure any consistency between the different chapters, since I would prefer that this volume instead serve as a useful forum for the...
Quantum spin transport in semiconductor nanostructures
Energy Technology Data Exchange (ETDEWEB)
Schindler, Christoph
2012-05-15
In this work, we study and quantitatively predict the quantum spin Hall effect, the spin-orbit interaction induced intrinsic spin-Hall effect, spin-orbit induced magnetizations, and spin-polarized electric currents in nanostructured two-dimensional electron or hole gases with and without the presence of magnetic fields. We propose concrete device geometries for the generation, detection, and manipulation of spin polarization and spin-polarized currents. To this end a novel multi-band quantum transport theory, that we termed the multi-scattering Buettiker probe model, is developed. The method treats quantum interference and coherence in open quantum devices on the same footing as incoherent scattering and incorporates inhomogeneous magnetic fields in a gauge-invariant and nonperturbative manner. The spin-orbit interaction parameters that control effects such as band energy spin splittings, g-factors, and spin relaxations are calculated microscopically in terms of an atomistic relativistic tight-binding model. We calculate the transverse electron focusing in external magnetic and electric fields. We have performed detailed studies of the intrinsic spin-Hall effect and its inverse effect in various material systems and geometries. We find a geometry dependent threshold value for the spin-orbit interaction for the inverse intrinsic spin-Hall effect that cannot be met by n-type GaAs structures. We propose geometries that spin polarize electric current in zero magnetic field and analyze the out-of-plane spin polarization by all electrical means. We predict unexpectedly large spin-orbit induced spin-polarization effects in zero magnetic fields that are caused by resonant enhancements of the spin-orbit interaction in specially band engineered and geometrically designed p-type nanostructures. We propose a concrete realization of a spin transistor in HgTe quantum wells, that employs the helical edge channel in the quantum spin Hall effect.
Quantum spin transport in semiconductor nanostructures
International Nuclear Information System (INIS)
Schindler, Christoph
2012-01-01
In this work, we study and quantitatively predict the quantum spin Hall effect, the spin-orbit interaction induced intrinsic spin-Hall effect, spin-orbit induced magnetizations, and spin-polarized electric currents in nanostructured two-dimensional electron or hole gases with and without the presence of magnetic fields. We propose concrete device geometries for the generation, detection, and manipulation of spin polarization and spin-polarized currents. To this end a novel multi-band quantum transport theory, that we termed the multi-scattering Buettiker probe model, is developed. The method treats quantum interference and coherence in open quantum devices on the same footing as incoherent scattering and incorporates inhomogeneous magnetic fields in a gauge-invariant and nonperturbative manner. The spin-orbit interaction parameters that control effects such as band energy spin splittings, g-factors, and spin relaxations are calculated microscopically in terms of an atomistic relativistic tight-binding model. We calculate the transverse electron focusing in external magnetic and electric fields. We have performed detailed studies of the intrinsic spin-Hall effect and its inverse effect in various material systems and geometries. We find a geometry dependent threshold value for the spin-orbit interaction for the inverse intrinsic spin-Hall effect that cannot be met by n-type GaAs structures. We propose geometries that spin polarize electric current in zero magnetic field and analyze the out-of-plane spin polarization by all electrical means. We predict unexpectedly large spin-orbit induced spin-polarization effects in zero magnetic fields that are caused by resonant enhancements of the spin-orbit interaction in specially band engineered and geometrically designed p-type nanostructures. We propose a concrete realization of a spin transistor in HgTe quantum wells, that employs the helical edge channel in the quantum spin Hall effect.
Relativistic Quantum Transport in Graphene Systems
2015-07-09
Enhancement of quantum entanglement by nonlinear dynamics in optomechanical systems...Nonlinear dynamics and quantum entanglement in optomechanical systems,” Physical Review Letters 112, 110406, 1-6 (2014). 12. L. Ying, Y.-C. Lai, and...interact with the potential barrier, however, can lead to relatively strong tunneling. In a small energy interval the quantum tunneling rate can thus
Spin and edge channel dependent transport through quantum dots
Energy Technology Data Exchange (ETDEWEB)
Ridder, T; Rogge, M C; Haug, R J [Institut fuer Festkoerperphysik, Gottfried Wilhelm Leibniz Universitaet Hannover, Appelstrasse 2, D-30167 Hannover (Germany)], E-mail: ridder@nano.uni-hannover.de
2008-11-12
We investigate the influence of spin polarized currents and non-equilibrated edge channels on the transport properties of a single quantum dot. Polarized currents are realized by the manual depletion of edge channels in high magnetic fields via a metallic top gate covering the source contact in the system. We observe a suppression and enhancement in the conductance of the quantum dot dependent on the edge channel configuration in the leads.
Security enhanced memory for quantum state.
Mukai, Tetsuya
2017-07-27
Security enhancement is important in terms of both classical and quantum information. The recent development of a quantum storage device is noteworthy, and a coherence time of one second or longer has been demonstrated. On the other hand, although the encryption of a quantum bit or quantum memory has been proposed theoretically, no experiment has yet been carried out. Here we report the demonstration of a quantum memory with an encryption function that is realized by scrambling and retrieving the recorded quantum phase. We developed two independent Ramsey interferometers on an atomic ensemble trapped below a persistent supercurrent atom chip. By operating the two interferometers with random phases, the quantum phase recorded by a pulse of the first interferometer was modulated by the second interferometer pulse. The scrambled quantum phase was restored by employing another pulse of the second interferometer with a specific time delay. This technique paves way for improving the security of quantum information technology.
Quantum Transport Through Tunable Molecular Diodes
Obodo, Tobechukwu Joshua
2017-07-31
Employing self-interaction corrected density functional theory combined with the non-equilibrium Green\\'s function method, we study the quantum transport through molecules with different numbers of phenyl (donor) and pyrimidinyl (acceptor) rings in order to evaluate the effects of the molecular composition on the transport properties. Excellent agreement with the results of recent experiments addressing the rectification behavior of molecular junctions is obtained, which demonstrates the potential of quantum transport simulations for designing high performance junctions by tuning the molecular specifications.
Quantum Transport Simulations of Nanoscale Materials
Obodo, Tobechukwu Joshua
2016-01-07
two dipyrimidinyl-diphenyl molecules improves the rectification ratio, and tuning the asymmetry of the tandem set-up by rearranging the molecular blocks greatly enhances it. It has been recently demonstrated that the large band gap of boronitrene can be significantly reduced by carbon functionalization. We show that specific defect configurations can result in metallicity, raising interest in the material for electronic applications. In particular, we demonstrate negative differential conductance with high peak-to-valley ratios, depending on the details of the material, and identify the finite bias effects that are responsible for this behavior. Also, we studied the spin polarized transport through Mn-decorated topological line defects in graphene. Strong preferential bonding is found, which overcomes the high mobility of transition metal atoms on graphene and results in stable structures. Despite a large distance between the magnetic centers, we find a high magnetoresistance and attribute this unexpected property to very strong induced π magnetism. Finally, the results obtained herein advance the field of quantum electronic transport and provide significant insight on switches, rectification, negative differential conductance, magnetoresistance, and current-induced forces of novel nanoscale materials.
Enhancing quantum sensing sensitivity by a quantum memory.
Zaiser, Sebastian; Rendler, Torsten; Jakobi, Ingmar; Wolf, Thomas; Lee, Sang-Yun; Wagner, Samuel; Bergholm, Ville; Schulte-Herbrüggen, Thomas; Neumann, Philipp; Wrachtrup, Jörg
2016-08-10
In quantum sensing, precision is typically limited by the maximum time interval over which phase can be accumulated. Memories have been used to enhance this time interval beyond the coherence lifetime and thus gain precision. Here, we demonstrate that by using a quantum memory an increased sensitivity can also be achieved. To this end, we use entanglement in a hybrid spin system comprising a sensing and a memory qubit associated with a single nitrogen-vacancy centre in diamond. With the memory we retain the full quantum state even after coherence decay of the sensor, which enables coherent interaction with distinct weakly coupled nuclear spin qubits. We benchmark the performance of our hybrid quantum system against use of the sensing qubit alone by gradually increasing the entanglement of sensor and memory. We further apply this quantum sensor-memory pair for high-resolution NMR spectroscopy of single (13)C nuclear spins.
Transport in the quantum critical regime
Enss, Tilman
2014-05-01
In this talk I will explain the relevance of the quantum critical point for the phase diagram of the unitary Fermi gas, briefly review theoretical approaches, and present results for the shear viscosity and spin diffusion in strongly interacting Fermi gases. The unitary Fermi gas describes strongly interacting fermions ranging from ultracold atoms near a Feshbach resonance to dilute neutron matter, which share a common universal phase diagram. The behavior at finite temperature is governed by a quantum critical point (QCP) at zero temperature and zero density, and observables can be expressed by universal scaling functions of the distance from the critical point. In the quantum critical regime above the QCP, thermal and quantum fluctuations are equally important, and the absence of a small parameter makes the computation of critical properties demanding. I will mention two theoretical approaches to transport properties in this regime: the large-N expansion in the number of fermion flavors allows for a systematic and controlled expansion even at strong coupling and elucidates the importance of medium effects on scattering. Second, the Luttinger-Ward, or self-consistent T-matrix approach goes beyond the quasiparticle picture and also explains universal high-energy tails. I will present results on the shear viscosity, or internal friction, for mass transport and show that the strongly interacting Fermi gas is an almost perfect quantum fluid. On the other hand, if particles of different spin move in opposite directions, the dynamics are governed by spin diffusion. One can distinguish longitudinal diffusion, when atomic clouds of different spin collide, and transverse diffusion, when the magnetization is wound up in a helix in a spin-echo experiment. Medium scattering and spin rotation have a strong effect on spin diffusion, and I will discuss how spin transport becomes very slow at strong coupling in the quantum degenerate regime and reaches a quantum limit of
Quantum transport through aromatic molecules
Energy Technology Data Exchange (ETDEWEB)
Ojeda, J. H., E-mail: judith.ojeda@uptc.edu.co [Instituto de Alta investigación, Universidad de Tarapaca, Casilla 7D Arica (Chile); Grupo de Física de Materiales, Escuela de Física, Universidad Pedagógica y Tecnológica de Colombia, Tunja (Colombia); Rey-González, R. R. [Departamento de Física, Universidad Nacional de Colombia, Bogotá D. C. (Colombia); Laroze, D. [Instituto de Alta investigación, Universidad de Tarapaca, Casilla 7D Arica (Chile)
2013-12-07
In this paper, we study the electronic transport properties through aromatic molecules connected to two semi-infinite leads. The molecules are in different geometrical configurations including arrays. Using a nearest neighbor tight-binding approach, the transport properties are analyzed into a Green's function technique within a real-space renormalization scheme. We calculate the transmission probability and the Current-Voltage characteristics as a function of a molecule-leads coupling parameter. Our results show different transport regimes for these systems, exhibiting metal-semiconductor-insulator transitions and the possibility to employ them in molecular devices.
Jung, Mi-Hee; Chu, Moo-Jung
2014-07-01
In this research, we prepared composite films via covalent coupling of CdSe quantum dots (QDs) to graphene through the direct binding of aryl radicals to the graphene surface. To compare the carrier transport with the CdSe aryl binding graphene film, we prepared CdSe pyridine capping graphene films through the pi-pi interactions of noncovalent bonds between the graphene and pyridine molecules. The photovoltaic devices were fabricated from the two hybrid films using the electrophoretic deposition method on flexible substrates. Even though the two hybrid films have the same amount of QDs and graphene, time-resolved fluorescence emission decay results show that the emission lifetime of the CdSe aryl group binding graphene film is significantly shorter than that of the pyridine capping CdSe-graphene. The quantum efficiency and photocurrent density of the device fabricated from CdSe aryl binding graphene were also higher than those of the device fabricated from pyridine capping CdSe-graphene. These results indicated that the carrier transport of the QD-graphene system is not related to the additive effect from the CdSe and graphene components but rather is a result of the unique interactions between the graphene and QDs. We could expect that these results can be useful in designing QD-graphene composite materials, which are applied in photovoltaic devices.
Jung, Mi-Hee; Chu, Moo-Jung
2014-08-07
In this research, we prepared composite films via covalent coupling of CdSe quantum dots (QDs) to graphene through the direct binding of aryl radicals to the graphene surface. To compare the carrier transport with the CdSe aryl binding graphene film, we prepared CdSe pyridine capping graphene films through the pi-pi interactions of noncovalent bonds between the graphene and pyridine molecules. The photovoltaic devices were fabricated from the two hybrid films using the electrophoretic deposition method on flexible substrates. Even though the two hybrid films have the same amount of QDs and graphene, time-resolved fluorescence emission decay results show that the emission lifetime of the CdSe aryl group binding graphene film is significantly shorter than that of the pyridine capping CdSe-graphene. The quantum efficiency and photocurrent density of the device fabricated from CdSe aryl binding graphene were also higher than those of the device fabricated from pyridine capping CdSe-graphene. These results indicated that the carrier transport of the QD-graphene system is not related to the additive effect from the CdSe and graphene components but rather is a result of the unique interactions between the graphene and QDs. We could expect that these results can be useful in designing QD-graphene composite materials, which are applied in photovoltaic devices.
Enhancing the Charging Power of Quantum Batteries.
Campaioli, Francesco; Pollock, Felix A; Binder, Felix C; Céleri, Lucas; Goold, John; Vinjanampathy, Sai; Modi, Kavan
2017-04-14
Can collective quantum effects make a difference in a meaningful thermodynamic operation? Focusing on energy storage and batteries, we demonstrate that quantum mechanics can lead to an enhancement in the amount of work deposited per unit time, i.e., the charging power, when N batteries are charged collectively. We first derive analytic upper bounds for the collective quantum advantage in charging power for two choices of constraints on the charging Hamiltonian. We then demonstrate that even in the absence of quantum entanglement this advantage can be extensive. For our main result, we provide an upper bound to the achievable quantum advantage when the interaction order is restricted; i.e., at most k batteries are interacting. This constitutes a fundamental limit on the advantage offered by quantum technologies over their classical counterparts.
Enhanced thermoelectric properties in boron nitride quantum-dot
Pan, Changning; Long, Mengqiu; He, Jun
We have investigated the ballistic thermoelectric properties in boron nitride quantum dots by using the nonequilibrium Green's function approach and the Landauer transport theory. The result shows that the phonon transport is substantially suppressed by the interface in the quantum dots. The resonant tunneling effect of electron leads to the fluctuations of the electronic conductance. It enhances significantly the Seebeck coefficient. Combined with the low thermal conductance of phonon, the high thermoelectric figure of merit ZT ∼0.78 can be obtained at room temperature T = 300 K and ZT ∼0.95 at low temperature T = 100 K. It is much higher than that of graphene quantum dots with the same geometry parameters, which is ZT ∼0.29 at room temperature T = 300 K and ZT ∼0.48 at low temperature T = 100 K. The underlying mechanism is that the boron nitride quantum dots possess higher thermopower and lower phonon thermal conductance than the graphene quantum dots. Thus the results indicate that the thermoelectric properties of boron nitride can be significantly enhanced by the quantum dot and are better than those of graphene.
Kwant: a software package for quantum transport
International Nuclear Information System (INIS)
Groth, Christoph W; Waintal, Xavier; Wimmer, Michael; Akhmerov, Anton R
2014-01-01
Kwant is a Python package for numerical quantum transport calculations. It aims to be a user-friendly, universal, and high-performance toolbox for the simulation of physical systems of any dimensionality and geometry that can be described by a tight-binding model. Kwant has been designed such that the natural concepts of the theory of quantum transport (lattices, symmetries, electrodes, orbital/spin/electron-hole degrees of freedom) are exposed in a simple and transparent way. Defining a new simulation setup is very similar to describing the corresponding mathematical model. Kwant offers direct support for calculations of transport properties (conductance, noise, scattering matrix), dispersion relations, modes, wave functions, various Green's functions, and out-of-equilibrium local quantities. Other computations involving tight-binding Hamiltonians can be implemented easily thanks to its extensible and modular nature. Kwant is free software available at http://kwant-project.org/. (paper)
Trautmann, N.; Hauke, P.
2018-02-01
The transport of excitations governs fundamental properties of matter. Particularly rich physics emerges in the interplay between disorder and environmental noise, even in small systems such as photosynthetic biomolecules. Counterintuitively, noise can enhance coherent quantum transport, which has been proposed as a mechanism behind the high transport efficiencies observed in photosynthetic complexes. This effect has been called "environment-assisted quantum transport". Here, we propose a quantum simulation of the excitation transport in an open quantum network, taking advantage of the high controllability of current trapped-ion experiments. Our scheme allows for the controlled study of various different aspects of the excitation transfer, ranging from the influence of static disorder and interaction range, over the effect of Markovian and non-Markovian dephasing, to the impact of a continuous insertion of excitations. Our paper discusses experimental error sources and realistic parameters, showing that it can be implemented in state-of-the-art ion-chain experiments.
Quantum transport in carbon nanotubes
Laird, E.A.; Kuemmeth, F.; Steele, G.A.; Grove-Rasmussen, K.; Nygard, J.; Flensberg, K.; Kouwenhoven, L.P.
2015-01-01
Carbon nanotubes are a versatile material in which many aspects of condensed matter physics come together. Recent discoveries have uncovered new phenomena that completely change our understanding of transport in these devices, especially the role of the spin and valley degrees of freedom. This
Quantum transport in semiconductor nanowires
Van Dam, J.
2006-01-01
This thesis describes a series of experiments aimed at understanding the low-temperature electrical transport properties of semiconductor nanowires. The semiconductor nanowires (1-100 nm in diameter) are grown from nanoscale gold particles via a chemical process called vapor-liquid-solid (VLS)
Quantum transport in carbon nanotubes
Jarillo-Herrero, P.D.
2005-01-01
Electronic transport through nanostructures can be very different from trans- port in macroscopic conductors, especially at low temperatures. Carbon na- notubes are tiny cylinders made of carbon atoms. Their remarkable electronic and mechanical properties, together with their small size (a few nm in
Quantum transport through single molecules
Osorio Oliveros, E.A.
2009-01-01
This thesis describes three-terminal transport measurements through single molecules. The interest in this field stems from the dream that single molecules will form the building blocks for future nanoscale electronic devices. The advantages are their small size -nanometers-, and their synthetic
Exciton size and quantum transport in nanoplatelets
Energy Technology Data Exchange (ETDEWEB)
Pelzer, Kenley M., E-mail: kpelzer@anl.gov; Gray, Stephen K. [Center for Nanoscale Materials, Argonne National Laboratory, 9700 Cass Ave., Argonne, Illinois 60439 (United States); Darling, Seth B. [Center for Nanoscale Materials, Argonne National Laboratory, 9700 Cass Ave., Argonne, Illinois 60439 (United States); Institute for Molecular Engineering, University of Chicago, 5747 S. Ellis Ave., Chicago, Illinois 60637 (United States); Schaller, Richard D. [Center for Nanoscale Materials, Argonne National Laboratory, 9700 Cass Ave., Argonne, Illinois 60439 (United States); Department of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston, Illinois 60208 (United States)
2015-12-14
Two-dimensional nanoplatelets (NPLs) are an exciting class of materials with promising optical and energy transport properties. The possibility of efficient energy transport between nanoplatelets raises questions regarding the nature of energy transfer in these thin, laterally extended systems. A challenge in understanding exciton transport is the uncertainty regarding the size of the exciton. Depending on the material and defects in the nanoplatelet, an exciton could plausibly extend over an entire plate or localize to a small region. The variation in possible exciton sizes raises the question how exciton size impacts the efficiency of transport between nanoplatelet structures. Here, we explore this issue using a quantum master equation approach. This method goes beyond the assumptions of Förster theory to allow for quantum mechanical effects that could increase energy transfer efficiency. The model is extremely flexible in describing different systems, allowing us to test the effect of varying the spatial extent of the exciton. We first discuss qualitative aspects of the relationship between exciton size and transport and then conduct simulations of exciton transport between NPLs for a range of exciton sizes and environmental conditions. Our results reveal that exciton size has a strong effect on energy transfer efficiency and suggest that manipulation of exciton size may be useful in designing NPLs for energy transport.
Detecting monopole charge via quantum interference transport
Dai, Xin; Lu, Haizhou; Yao, Hong
Topological Weyl and double-Weyl semimetals host different monopole charges in momentum space. How to detect the signature of the monopole charges in quantum transport remains a challenging topic. Here, we reveal the connection between the parity of monopole charge in topological semimetals and the quantum-interference correction to the conductivity. We demonstrate that the parity of monopole charge determines the sign of quantum-interfere correction, with odd and even parity yielding the weak anti-localization and weak localization effect, respectively. This is attributed to the Berry phase difference between time-reversed trajectories circulating the great circle of the Fermi sphere that encloses the monopole charges. From standard Feynman diagram calculations, we further show that the weak-field magnetoconductivity is proportional to +/-√{ B} for double-Weyl semimetals and Weyl semimetals, respectively, which could be verified experimentally.
Dephasing-assisted transport: quantum networks and biomolecules
International Nuclear Information System (INIS)
Plenio, M B; Huelga, S F
2008-01-01
Transport phenomena are fundamental in physics. They allow for information and energy to be exchanged between individual constituents of communication systems, networks or even biological entities. Environmental noise will generally hinder the efficiency of the transport process. However, and contrary to intuition, there are situations in classical systems where thermal fluctuations are actually instrumental in assisting transport phenomena. Here we show that, even at zero temperature, transport of excitations across dissipative quantum networks can be enhanced by local dephasing noise. We explain the underlying physical mechanisms behind this phenomenon and propose possible experimental demonstrations in quantum optics. Our results suggest that the presence of entanglement does not play an essential role for energy transport and may even hinder it. We argue that Nature may be routinely exploiting dephasing noise and show that the transport of excitations in simplified models of light harvesting molecules does benefit from such noise assisted processes. These results point toward the possibility for designing optimized structures for transport, for example in artificial nanostructures, assisted by noise.
Quantum Simulator for Transport Phenomena in Fluid Flows
Mezzacapo, A.; Sanz, M.; Lamata, L.; Egusquiza, I. L.; Succi, S.; Solano, E.
2015-08-01
Transport phenomena still stand as one of the most challenging problems in computational physics. By exploiting the analogies between Dirac and lattice Boltzmann equations, we develop a quantum simulator based on pseudospin-boson quantum systems, which is suitable for encoding fluid dynamics transport phenomena within a lattice kinetic formalism. It is shown that both the streaming and collision processes of lattice Boltzmann dynamics can be implemented with controlled quantum operations, using a heralded quantum protocol to encode non-unitary scattering processes. The proposed simulator is amenable to realization in controlled quantum platforms, such as ion-trap quantum computers or circuit quantum electrodynamics processors.
Coherent transport through interacting quantum dots
Energy Technology Data Exchange (ETDEWEB)
Hiltscher, Bastian
2012-10-05
The present thesis is composed of four different works. All deal with coherent transport through interacting quantum dots, which are tunnel-coupled to external leads. There a two main motivations for the use of quantum dots. First, they are an ideal device to study the influence of strong Coulomb repulsion, and second, their discrete energy levels can easily be tuned by external gate electrodes to create different transport regimes. The expression of coherence includes a very wide range of physical correlations and, therefore, the four works are basically independent of each other. Before motivating and introducing the different works in more detail, we remark that in all works a diagrammatic real-time perturbation theory is used. The fermionic degrees of freedom of the leads are traced out and the elements of the resulting reduced density matrix can be treated explicitly by means of a generalized master equation. How this equation is solved, depends on the details of the problem under consideration. In the first of the four works adiabatic pumping through an Aharonov-Bohm interferometer with a quantum dot embedded in each of the two arms is studied. In adiabatic pumping transport is generated by varying two system parameters periodically in time. We consider the two dot levels to be these two pumping parameters. Since they are located in different arms of the interferometer, pumping is a quantum mechanical effect purely relying on coherent superpositions of the dot states. It is very challenging to identify a quantum pumping mechanism in experiments, because a capacitive coupling of the gate electrodes to the leads may yield an undesired AC bias voltage, which is rectified by a time dependent conductance. Therefore, distinguishing features of these two transport mechanisms are required. We find that the dependence on the magnetic field is the key feature. While the pumped charge is an odd function of the magnetic flux, the rectified current is even, at least in
Coherent transport through interacting quantum dots
International Nuclear Information System (INIS)
Hiltscher, Bastian
2012-01-01
The present thesis is composed of four different works. All deal with coherent transport through interacting quantum dots, which are tunnel-coupled to external leads. There a two main motivations for the use of quantum dots. First, they are an ideal device to study the influence of strong Coulomb repulsion, and second, their discrete energy levels can easily be tuned by external gate electrodes to create different transport regimes. The expression of coherence includes a very wide range of physical correlations and, therefore, the four works are basically independent of each other. Before motivating and introducing the different works in more detail, we remark that in all works a diagrammatic real-time perturbation theory is used. The fermionic degrees of freedom of the leads are traced out and the elements of the resulting reduced density matrix can be treated explicitly by means of a generalized master equation. How this equation is solved, depends on the details of the problem under consideration. In the first of the four works adiabatic pumping through an Aharonov-Bohm interferometer with a quantum dot embedded in each of the two arms is studied. In adiabatic pumping transport is generated by varying two system parameters periodically in time. We consider the two dot levels to be these two pumping parameters. Since they are located in different arms of the interferometer, pumping is a quantum mechanical effect purely relying on coherent superpositions of the dot states. It is very challenging to identify a quantum pumping mechanism in experiments, because a capacitive coupling of the gate electrodes to the leads may yield an undesired AC bias voltage, which is rectified by a time dependent conductance. Therefore, distinguishing features of these two transport mechanisms are required. We find that the dependence on the magnetic field is the key feature. While the pumped charge is an odd function of the magnetic flux, the rectified current is even, at least in
Acoustically enhanced heat transport
Energy Technology Data Exchange (ETDEWEB)
Ang, Kar M.; Hung, Yew Mun; Tan, Ming K., E-mail: tan.ming.kwang@monash.edu [School of Engineering, Monash University Malaysia, 47500 Bandar Sunway, Selangor (Malaysia); Yeo, Leslie Y. [Micro/Nanophysics Research Laboratory, RMIT University, Melbourne, VIC 3001 (Australia); Friend, James R. [Department of Mechanical and Aerospace Engineering, University of California, San Diego, California 92093 (United States)
2016-01-15
We investigate the enhancement of heat transfer in the nucleate boiling regime by inducing high frequency acoustic waves (f ∼ 10{sup 6} Hz) on the heated surface. In the experiments, liquid droplets (deionized water) are dispensed directly onto a heated, vibrating substrate. At lower vibration amplitudes (ξ{sub s} ∼ 10{sup −9} m), the improved heat transfer is mainly due to the detachment of vapor bubbles from the heated surface and the induced thermal mixing. Upon increasing the vibration amplitude (ξ{sub s} ∼ 10{sup −8} m), the heat transfer becomes more substantial due to the rapid bursting of vapor bubbles happening at the liquid-air interface as a consequence of capillary waves travelling in the thin liquid film between the vapor bubble and the air. Further increases then lead to rapid atomization that continues to enhance the heat transfer. An acoustic wave displacement amplitude on the order of 10{sup −8} m with 10{sup 6} Hz order frequencies is observed to produce an improvement of up to 50% reduction in the surface temperature over the case without acoustic excitation.
Acoustically enhanced heat transport
Ang, Kar M.; Yeo, Leslie Y.; Friend, James R.; Hung, Yew Mun; Tan, Ming K.
2016-01-01
We investigate the enhancement of heat transfer in the nucleate boiling regime by inducing high frequency acoustic waves (f ˜ 106 Hz) on the heated surface. In the experiments, liquid droplets (deionized water) are dispensed directly onto a heated, vibrating substrate. At lower vibration amplitudes (ξs ˜ 10-9 m), the improved heat transfer is mainly due to the detachment of vapor bubbles from the heated surface and the induced thermal mixing. Upon increasing the vibration amplitude (ξs ˜ 10-8 m), the heat transfer becomes more substantial due to the rapid bursting of vapor bubbles happening at the liquid-air interface as a consequence of capillary waves travelling in the thin liquid film between the vapor bubble and the air. Further increases then lead to rapid atomization that continues to enhance the heat transfer. An acoustic wave displacement amplitude on the order of 10-8 m with 106 Hz order frequencies is observed to produce an improvement of up to 50% reduction in the surface temperature over the case without acoustic excitation.
Quantum-enhanced sensing from hyperentanglement
Walborn, S. P.; Pimentel, A. H.; Davidovich, L.; de Matos Filho, R. L.
2018-01-01
Hyperentanglement—simultaneous entanglement between multiple degrees of freedom of two or more systems—has been used to enhance quantum information tasks such as quantum communication and photonic quantum computing. Here we show that hyperentanglement can lead to increased quantum advantage in metrology, with contributions from the entanglement in each degree of freedom, allowing for Heisenberg scaling in the precision of parameter estimation. Our experiment employs photon pairs entangled in polarization and spatial degrees of freedom to estimate a small tilt angle of a mirror. Precision limits beyond shot noise are saturated through a simple binary measurement of the polarization state. The dynamics considered here have broad applicability, implying that similar strategies based on hyperentanglement can offer improvement in a wide variety of physical scenarios and metrological tasks.
Dephasing-assisted selective incoherent quantum transport
Behzadi, Naghi; Ahansaz, Bahram; Kasani, Hadi
2015-10-01
Selective energy transport throughout a quantum network connected to more than one reaction center can play an important role in many natural and technological considerations in photosystems. In this work, we propose a method in which an excitation can be transported from the original site of the network to one of the reaction centers arbitrarily using independent sources of dephasing noises. We demonstrate that in the absence of dephasing noises, the coherent evolution of the system does not have any role in energy transport in the network. Therefore, incoherent evolution via application of dephasing noises throughout a selected path of the network leads to complete transferring of the excitation to a desired reaction center.
Cao, Sheng
2017-04-19
Colloidal ZnO nanoparticle (NP) films are recognized as efficient electron transport layers (ETLs) for quantum dot light-emitting diodes (QD-LEDs) with good stability and high efficiency. However, because of the inherently high work function of such films, spontaneous charge transfer occurs at the QD/ZnO interface in such a QD-LED, thus leading to reduced performance. Here, to improve the QD-LED performance, we prepared Ga-doped ZnO NPs with low work functions and tailored band structures via a room-temperature (RT) solution process without the use of bulky organic ligands. We found that the charge transfer at the interface between the CdSe/ZnS QDs and the doped ZnO NPs was significantly weakened because of the incorporated Ga dopants. Remarkably, the as-assembled QD-LEDs, with Ga-doped ZnO NPs as the ETLs, exhibited superior luminances of up to 44 000 cd/m2 and efficiencies of up to 15 cd/A, placing them among the most efficient red-light QD-LEDs ever reported. This discovery provides a new strategy for fabricating high-performance QD-LEDs by using RT-processed Ga-doped ZnO NPs as the ETLs, which could be generalized to improve the efficiency of other optoelectronic devices.
Scaling theory for anomalous semiclassical quantum transport
Sena-Junior, M. I.; Macêdo, A. M. S.
2016-01-01
Quantum transport through devices coupled to electron reservoirs can be described in terms of the full counting statistics (FCS) of charge transfer. Transport observables, such as conductance and shot-noise power are just cumulants of FCS and can be obtained from the sample's average density of transmission eigenvalues, which in turn can be obtained from a finite element representation of the saddle-point equation of the Keldysh (or supersymmetric) nonlinear sigma model, known as quantum circuit theory. Normal universal metallic behavior in the semiclassical regime is controlled by the presence of a Fabry-Pérot singularity in the average density of transmission eigenvalues. We present general conditions for the suppression of Fabry-Pérot modes in the semiclassical regime in a sample of arbitrary shape, a disordered conductor or a network of ballistic quantum dots, which leads to an anomalous metallic phase. Through a double-scaling limit, we derive a scaling equation for anomalous metallic transport, in the form of a nonlinear differential equation, which generalizes the ballistic-diffusive scaling equation of a normal metal. The two-parameter stationary solution of our scaling equation generalizes Dorokhov's universal single-parameter distribution of transmission eigenvalues. We provide a simple interpretation of the stationary solution using a thermodynamic analogy with a spin-glass system. As an application, we consider a system formed by a diffusive wire coupled via a barrier to normal-superconductor reservoirs. We observe anomalous reflectionless tunneling, when all perfectly transmitting channels are suppressed, which cannot be explained by the usual mechanism of disorder-induced opening of tunneling channels.
Quantum transport of the single metallocene molecule
Yu, Jing-Xin; Chang, Jing; Wei, Rong-Kai; Liu, Xiu-Ying; Li, Xiao-Dong
2016-10-01
The Quantum transport of three single metallocene molecule is investigated by performing theoretical calculations using the non-equilibrium Green's function method combined with density functional theory. We find that the three metallocen molecules structure become stretched along the transport direction, the distance between two Cp rings longer than the other theory and experiment results. The lager conductance is found in nickelocene molecule, the main transmission channel is the electron coupling between molecule and the electrodes is through the Ni dxz and dyz orbitals and the s, dxz, dyz of gold. This is also confirmed by the highest occupied molecular orbital resonance at Fermi level. In addition, negative differential resistance effect is found in the ferrocene, cobaltocene molecules, this is also closely related with the evolution of the transmission spectrum under applied bias.
Nonlinearities in reservoir engineering: Enhancing quantum correlations
Hu, Xiangming; Hu, Qingping; Li, Lingchao; Huang, Chen; Rao, Shi
2017-12-01
There are two decisive factors for quantum correlations in reservoir engineering, but they are strongly reversely dependent on the atom-field nonlinearities. One is the squeezing parameter for the Bogoliubov modes-mediated collective interactions, while the other is the dissipative rates for the engineered collective dissipations. Exemplifying two-level atomic ensembles, we show that the moderate nonlinearities can compromise these two factors and thus enhance remarkably two-mode squeezing and entanglement of different spin atomic ensembles or different optical fields. This suggests that the moderate nonlinearities of the two-level systems are more advantageous for applications in quantum networks associated with reservoir engineering.
Statistical theory of designed quantum transport across disordered networks
Walschaers, Mattia; Mulet, Roberto; Wellens, Thomas; Buchleitner, Andreas
2015-04-01
We explain how centrosymmetry, together with a dominant doublet of energy eigenstates in the local density of states, can guarantee interference-assisted, strongly enhanced, strictly coherent quantum excitation transport between two predefined sites of a random network of two-level systems. Starting from a generalization of the chaos-assisted tunnelling mechanism, we formulate a random matrix theoretical framework for the analytical prediction of the transfer time distribution, of lower bounds of the transfer efficiency, and of the scaling behavior of characteristic statistical properties with the size of the network. We show that these analytical predictions compare well to numerical simulations, using Hamiltonians sampled from the Gaussian orthogonal ensemble.
Transport phenomena in the asymmetric quantum multibaker map.
Ermann, Leonardo; Carlo, Gabriel G; Saraceno, Marcos
2008-01-01
By studying a modified (unbiased) quantum multibaker map, we were able to obtain a finite asymptotic quantum current without a classical analog. This result suggests a general method for the design of purely quantum ratchets and sheds light on the investigation of the mechanisms leading to net transport generation by breaking symmetries of quantum systems. Moreover, we propose the multibaker map as a resource to study directed transport phenomena in chaotic systems without bias. In fact, this is a paradigmatic model in classical and quantum chaos, but also in statistical mechanics.
Quantum-Enhanced Cyber Security: Experimental Computation on Quantum-Encrypted Data
2017-03-02
AFRL-AFOSR-UK-TR-2017-0020 Quantum -Enhanced Cyber Security: Experimental Computation on Quantum -Encrypted Data Philip Walther UNIVERSITT WIEN Final...REPORT TYPE Final 3. DATES COVERED (From - To) 15 Oct 2015 to 31 Dec 2016 4. TITLE AND SUBTITLE Quantum -Enhanced Cyber Security: Experimental Computation ...project developed methods and technologies are necessary prerequisites for performing experimental quantum computations with quantum -encrypted data. Even
Enhancing robustness of multiparty quantum correlations using weak measurement
Energy Technology Data Exchange (ETDEWEB)
Singh, Uttam, E-mail: uttamsingh@hri.res.in [Quantum Information and Computation Group, Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211 019 (India); Mishra, Utkarsh, E-mail: utkarsh@hri.res.in [Quantum Information and Computation Group, Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211 019 (India); Dhar, Himadri Shekhar, E-mail: dhar.himadri@gmail.com [School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067 (India)
2014-11-15
Multipartite quantum correlations are important resources for the development of quantum information and computation protocols. However, the resourcefulness of multipartite quantum correlations in practical settings is limited by its fragility under decoherence due to environmental interactions. Though there exist protocols to protect bipartite entanglement under decoherence, the implementation of such protocols for multipartite quantum correlations has not been sufficiently explored. Here, we study the effect of local amplitude damping channel on the generalized Greenberger–Horne–Zeilinger state, and use a protocol of optimal reversal quantum weak measurement to protect the multipartite quantum correlations. We observe that the weak measurement reversal protocol enhances the robustness of multipartite quantum correlations. Further it increases the critical damping value that corresponds to entanglement sudden death. To emphasize the efficacy of the technique in protection of multipartite quantum correlation, we investigate two proximately related quantum communication tasks, namely, quantum teleportation in a one sender, many receivers setting and multiparty quantum information splitting, through a local amplitude damping channel. We observe an increase in the average fidelity of both the quantum communication tasks under the weak measurement reversal protocol. The method may prove beneficial, for combating external interactions, in other quantum information tasks using multipartite resources. - Highlights: • Extension of weak measurement reversal scheme to protect multiparty quantum correlations. • Protection of multiparty quantum correlation under local amplitude damping noise. • Enhanced fidelity of quantum teleportation in one sender and many receivers setting. • Enhanced fidelity of quantum information splitting protocol.
Quantum Transport in Strongly Correlated Systems
DEFF Research Database (Denmark)
Bohr, Dan
2007-01-01
the density matrix renormalization group (DMRG) method. We present two DMRG setups for calculating the linear conductance of strongly correlated nanostructures in the infinitesimal source-drain voltage regime. The first setup describes the leads by modified real-space tight-binding chains, whereas the second...... screening plays a much less significant role than in bulk systems due to the reduced size of the objects, therefore making it necessary to consider the importance of correlations between electrons. The work presented in this thesis deals with quantum transport through strongly correlated systems using....... Thus both coherence and correlation effects are important in this model, and the methods applied should be able to handle both these effects rigorously. We present the DMRG setup for this model and benchmark against existing Greens function results for the model. Then we present initial DMRG results...
Topological phases and transport properties of screened interacting quantum wires
Energy Technology Data Exchange (ETDEWEB)
Xu, Hengyi, E-mail: hengyi.xu@njnu.edu.cn [School of Physics and Technology, Nanjing Normal University, Nanjing 210023 (China); Xiong, Ye [School of Physics and Technology, Nanjing Normal University, Nanjing 210023 (China); Wang, Jun [Department of Physics, Southeast University, Nanjing 210096 (China)
2016-10-14
We study theoretically the effects of long-range and on-site Coulomb interactions on the topological phases and transport properties of spin–orbit-coupled quasi-one-dimensional quantum wires imposed on a s-wave superconductor. The distributions of the electrostatic potential and charge density are calculated self-consistently within the Hartree approximation. Due to the finite width of the wires and charge repulsion, the potential and density distribute inhomogeneously in the transverse direction and tend to accumulate along the lateral edges where the hard-wall confinement is assumed. This result has profound effects on the topological phases and the differential conductance of the interacting quantum wires and their hybrid junctions with superconductors. Coulomb interactions renormalize the gate voltage and alter the topological phases strongly by enhancing the topological regimes and producing jagged boundaries. Moreover, the multicritical points connecting different topological phases are modified remarkably in striking contrast to the predictions of the two-band model. We further suggest the possible non-magnetic topological phase transitions manipulated externally with the aid of long-range interactions. Finally, the transport properties of normal–superconductor junctions are further examined, in particular, the impacts of Coulomb interactions on the zero-bias peaks related to the Majorana fermions and near zero-energy peaks. - Highlights: • A model of the screened Coulomb interactions in Majorana wires is proposed. • The interacting topological phase diagrams in multiband quantum wires are revealed. • The Majorana fermions in interacting multiband quantum wires are investigated.
Transport Studies of Quantum Magnetism: Physics and Methods
Energy Technology Data Exchange (ETDEWEB)
Lee, Minhyea [Univ. of Colorado, Boulder, CO (United States)
2017-03-30
The main goal of this project was to understand novel ground states of spin systems probed by thermal and electrical transport measurements. They are well-suited to characterize the nature of low-energy excitations as unique property of the ground state. More specifically, it was aimed to study the transverse electrical conductivity in the presence of non-collinear and non-coplanar spin ordering and the effects of gauge field as well as novel spin excitations as a coherent heat transport channel in insulating quantum magnets. Most of works done during the grant period focused on these topics. As a natural extension of the project's initial goals, the scope was broadened to include transport studies on the spin systems with strong spin-orbit coupling. One particular focus was an exploration of systems with strong magnetic anisotropy combined with non-trivial spin configuration. Magnetic anisotropy is directly related to implement the non-collinear spin ordering to the existing common geometry of planar devices and thus poses a significant potential. Work in this direction includes the comparison of the topological Hall signal under hydrostatic pressure and chemical doping, as well as the angular dependence dependence of the non-collinear spin ordered phase and their evolution up on temperature and field strength. Another focus was centered around the experimental identification of spin-originated heat carrying excitation in quasi two dimensional honeycomb lattice, where Kitaev type of quantum spin liquid phase is expected to emerge. In fact, when its long range magnetic order is destroyed by the applied field, we discovered anomalously large enhancement of thermal conductivity, for which proximate Kitaev excitations in field-induced spin liquid state are responsible for. This work, combined with further investigations in materials in the similar class may help establish the experimental characterization of new quantum spin liquid and their unique low energy
Quantum electron transport in toroidal carbon nanotubes
Jack, Mark; Encinosa, Mario
2008-03-01
Electron transport under bias is treated in tight-binding approximation using a non-equilibrium Green's function approach. Density-of-states D(E), transmissivity T(E), and current ISD are calculated through a (3,3) armchair nanotorus with laterally attached metallic leads and a magnetic field penetrating the toroidal plane. Plateaus in T(E) through the torus are observed as a function of both the relative angle between leads and magnetic flux. Initial computational studies performed with 1800 atoms and attached leads show substantial computational slowdown when increasing the system size by a factor of two. Results are generated by inverting the device Hamiltonian with a standard recursion method extended to account for unit cell toroidal closure. Significant computational speed-up is expected for a parallelized code on a multiprocessor computer cluster. The dependence of electronic features on torus size and torus curvature is tested for three tori with 900, 1800 and 3600 carbon atoms, respectively. References: 1. M. Jack and M. Encinosa, Quantum electron transport in toroidal carbon nanotubes with metallic leads. ArXiv: quant-ph/0709.0760. 2. M. Encinosa and M. Jack, Dipole and solenoidal magnetic moments of electronic surface currents on toroidal nanostructures. J. Comp.-Aided Mat. Design (Springer), 14 (1) (2007) 65 -- 71.
Quantum Spin Transport in Mesoscopic Interferometer
Directory of Open Access Journals (Sweden)
Zein W. A.
2007-10-01
Full Text Available Spin-dependent conductance of ballistic mesoscopic interferometer is investigated. The quantum interferometer is in the form of ring, in which a quantum dot is embedded in one arm. This quantum dot is connected to one lead via tunnel barrier. Both Aharonov- Casher and Aharonov-Bohm e ects are studied. Our results confirm the interplay of spin-orbit coupling and quantum interference e ects in such confined quantum systems. This investigation is valuable for spintronics application, for example, quantum information processing.
Cui, Ping
The thesis comprises two major themes of quantum statistical dynamics. One is the development of quantum dissipation theory (QDT). It covers the establishment of some basic relations of quantum statistical dynamics, the construction of several nonequivalent complete second-order formulations, and the development of exact QDT. Another is related to the applications of quantum statistical dynamics to a variety of research fields. In particular, unconventional but novel theories of the electron transfer in Debye solvents, quantum transport, and quantum measurement are developed on the basis of QDT formulations. The thesis is organized as follows. In Chapter 1, we present some background knowledge in relation to the aforementioned two themes of this thesis. The key quantity in QDT is the reduced density operator rho(t) ≡ trBrho T(t); i.e., the partial trace of the total system and bath composite rhoT(t) over the bath degrees of freedom. QDT governs the evolution of reduced density operator, where the effects of bath are treated in a quantum statistical manner. In principle, the reduced density operator contains all dynamics information of interest. However, the conventional quantum transport theory is formulated in terms of nonequilibrium Green's function. The newly emerging field of quantum measurement in relation to quantum information and quantum computing does exploit a sort of QDT formalism. Besides the background of the relevant theoretical development, some representative experiments on molecular nanojunctions are also briefly discussed. In chapter 2, we outline some basic (including new) relations that highlight several important issues on QDT. The content includes the background of nonequilibrium quantum statistical mechanics, the general description of the total composite Hamiltonian with stochastic system-bath interaction, a novel parameterization scheme for bath correlation functions, a newly developed exact theory of driven Brownian oscillator (DBO
Quantum Thermal Transport in Semiconductor Nanostructures
Miao, Kai
Modern semiconductor devices scale down to the nanometer range. Heat dissipation becomes a critical issue in the chip design. From a different perspective, energy conservation has attracted much of attention from researchers. The essence of heat dissipation and energy conservation is the heat transport. Thermal properties of semiconductors have been under intense investigation in recent decades. Classical models fail to consider the quantum effects in devices on the scale of nanometers. First-principle methods only can deal with small devices and is computationally intensive. Instead, a modified valence force field (VFF) model is applied to reproduce the phonon properties of different materials and devices. Phonon transport is explored using the Green's functions. The concept of a Buttiker probe model is first used to mimic the scattering mechanisms in phonon transport. This energy conservation model is straightforward and efficient in describing scattering. In the quasiparticle approximation, phonon scattering will cause a phonon energy shift. This energy shift is represented by the scattering self-energy in a retarded Green's function. Phonon lifetime is extracted from the scattering self-energy expression. Different relaxation time approximation (RTA) models are studied and coupled with the phonon Green's function method for the first time. We prove that the widely used and proven RTA models in the Boltzmann transport equation (BTE) survive in the atomistic Green's function method. This method can give accurate thermal properties agreeing closely with the experimental results for bulk devices. This atomistic method can also consider quantum confinement effects at the nanoscale. The heat transport across a Si/Ge interface is introduced in this work as an example for this application. The heat transfer across metal/semiconductor (MS) interfaces is investigated as well. Relaxation at the interface can be done in two different ways. Using VFF model to relax the
Morrison, C.; Casteleiro, C.; Leadley, D. R.; Myronov, M.
2016-09-01
The complex quantum transport of a strained Ge quantum well (QW) modulation doped heterostructure with two types of mobile carriers has been observed. The two dimensional hole gas (2DHG) in the Ge QW exhibits an exceptionally high mobility of 780 000 cm2/Vs at temperatures below 10 K. Through analysis of Shubnikov de-Haas oscillations in the magnetoresistance of this 2DHG below 2 K, the hole effective mass is found to be 0.065 m0. Anomalous conductance peaks are observed at higher fields which deviate from standard Shubnikov de-Haas and quantum Hall effect behaviour due to conduction via multiple carrier types. Despite this complex behaviour, analysis using a transport model with two conductive channels explains this behaviour and allows key physical parameters such as the carrier effective mass, transport, and quantum lifetimes and conductivity of the electrically active layers to be extracted. This finding is important for electronic device applications, since inclusion of highly doped interlayers which are electrically active, for enhancement of, for example, room temperature carrier mobility, does not prevent analysis of quantum transport in a QW.
A quantum energy transport model for semiconductor device simulation
Energy Technology Data Exchange (ETDEWEB)
Sho, Shohiro, E-mail: shoshohiro@gmail.com [Graduate School of Information Science and Technology, Osaka University, Osaka (Japan); Odanaka, Shinji [Computer Assisted Science Division, Cybermedia Center, Osaka University, Osaka (Japan)
2013-02-15
This paper describes numerical methods for a quantum energy transport (QET) model in semiconductors, which is derived by using a diffusion scaling in the quantum hydrodynamic (QHD) model. We newly drive a four-moments QET model similar with a classical ET model. Space discretization is performed by a new set of unknown variables. Numerical stability and convergence are obtained by developing numerical schemes and an iterative solution method with a relaxation method. Numerical simulations of electron transport in a scaled MOSFET device are discussed. The QET model allows simulations of quantum confinement transport, and nonlocal and hot-carrier effects in scaled MOSFETs.
Quantum-enhanced micromechanical displacement sensitivity
DEFF Research Database (Denmark)
Hoff, Ulrich Busk; Harris, Glen I.; Madsen, Lars Skovgaard
2013-01-01
We report on a hitherto unexplored application of squeezed light: for quantum-enhancement of mechanical transduction sensitivity in microcavity optomechanics. Using a toroidal silica microcavity, we experimentally demonstrate measurement of the transduced phase modulation signal in the frequency...... range 4–5.8 MHz with a sensitivity −0.72(±0.01) dB below the shot noise level. This is achieved for resonant probing in the highly undercoupled regime, by preparing the probe in a weak coherent state with phase squeezed vacuum states at sideband frequencies....
Enhancement of electrocaloric response through quantum effects
Jouzdani, P.; Cuozzo, S.; Lisenkov, S.; Ponomareva, I.
2017-12-01
A semiclassical approach that incorporates quantum mechanical behavior of heat capacity in direct caloric effect simulations is proposed. Application of this methodology to study the electrocaloric effect in prototypical ferroelectrics PbTiO3 and BaTiO3 reveals severe underestimation of electrocaloric response at lowest temperatures by classical simulations. The discrepancy between semiclassical and classical results is found to be largest in ferroics with Debye temperature exceeding the Curie point. A route to enhance the electrocaloric effect by tuning the Debye temperature in composite materials is proposed.
23 CFR 710.511 - Transportation enhancements.
2010-04-01
... 23 Highways 1 2010-04-01 2010-04-01 false Transportation enhancements. 710.511 Section 710.511 Highways FEDERAL HIGHWAY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION RIGHT-OF-WAY AND ENVIRONMENT RIGHT-OF-WAY AND REAL ESTATE Property Acquisition Alternatives § 710.511 Transportation enhancements. (a...
Quantum-enhanced measurements: beating the standard quantum limit.
Giovannetti, Vittorio; Lloyd, Seth; Maccone, Lorenzo
2004-11-19
Quantum mechanics, through the Heisenberg uncertainty principle, imposes limits on the precision of measurement. Conventional measurement techniques typically fail to reach these limits. Conventional bounds to the precision of measurements such as the shot noise limit or the standard quantum limit are not as fundamental as the Heisenberg limits and can be beaten using quantum strategies that employ "quantum tricks" such as squeezing and entanglement.
Electron transport and coherence in semiconductor quantum dots and rings
Van der Wiel, W.G.
2002-01-01
A number of experiments on electron transport and coherence in semiconductor vertical and lateral quantum dots and semiconductor rings is described. Quantum dots are often referred to as "artificial atoms", because of their similarities with real atoms. Examples of such atom-like properties that
Rauf Abdullah, Nzar; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar
2016-09-21
We investigate theoretically the balance of the static magnetic and the dynamical photon forces in the electron transport through a quantum dot in a photon cavity with a single photon mode. The quantum dot system is connected to external leads and the total system is exposed to a static perpendicular magnetic field. We explore the transport characteristics through the system by tuning the ratio, [Formula: see text], between the photon energy, [Formula: see text], and the cyclotron energy, [Formula: see text]. Enhancement in the electron transport with increasing electron-photon coupling is observed when [Formula: see text]. In this case the photon field dominates and stretches the electron charge distribution in the quantum dot, extending it towards the contact area for the leads. Suppression in the electron transport is found when [Formula: see text], as the external magnetic field causes circular confinement of the charge density around the dot.
Nonequilibrium electron transport through quantum dots in the Kondo regime
DEFF Research Database (Denmark)
Wölfle, Peter; Paaske, Jens; Rosch, Achim
2005-01-01
Electron transport at large bias voltage through quantum dots in the Kondo regime is described within the perturbative renormalization group extended to nonequilibrium. The conductance, local magnetization, dynamical spin susceptibility and local spectral function are calculated. We show how the ...
Quantum transport: From effective mass approximation to full band
Fu, Bo
To study dissipative quantum transport in ultra-scaled devices, we first solve the Pauli Master Equation using the Effective Mass Approximation, followed by solving ballistic quantum transport using the full band structure determined from the empirical pseudopotential method. We study the geometry induced quantum access resistance, evaluate the influence of non-polar phonon scattering, and calculate impurity scattering in devices such as n-i-n resistor, Double-Barrier Resonant Tunneling Diode, Double-Gate Field Effect Transistors. We calculate band structure and the complex band structure of Silicon Nanowires, develop open boundary conditions for full band quantum transport using the empirical pseudopotential method, and perform atomistic modeling of Silicon Nanowire structures to study electron transport characteristics.
Perspective: Theory of quantum transport in molecular junctions
Thoss, Michael; Evers, Ferdinand
2018-01-01
Molecular junctions, where single molecules are bound to metal or semiconductor electrodes, represent a unique architecture to investigate molecules in a distinct nonequilibrium situation and, in a broader context, to study basic mechanisms of charge and energy transport in a many-body quantum system at the nanoscale. Experimental studies of molecular junctions have revealed a wealth of interesting transport phenomena, the understanding of which necessitates theoretical modeling. The accurate theoretical description of quantum transport in molecular junctions is challenging because it requires methods that are capable to describe the electronic structure and dynamics of molecules in a condensed phase environment out of equilibrium, in some cases with strong electron-electron and/or electronic-vibrational interaction. This perspective discusses recent progress in the theory and simulation of quantum transport in molecular junctions. Furthermore, challenges are identified, which appear crucial to achieve a comprehensive and quantitative understanding of transport in these systems.
Electron Transport in Coupled Quantum Dots
National Research Council Canada - National Science Library
Antoniadis, D
1998-01-01
In the course of the investigation funded by this proposal we fabricated, modeled, and measured a variety of quantum dot structures in order to better understand how such nanostructures might be used for computation...
Transport in quantum spin Hall edges in contact to a quantum dot
Rizzo, Bruno; Camjayi, Alberto; Arrachea, Liliana
2016-09-01
We study the transport mechanisms taking place in a quantum spin Hall bar with an embedded quantum dot, where electrons localize and experience Coulomb interaction U as well as spin-flip processes λ . We solve the problem with nonequilibrium Green functions. We focus on the linear-response regime and treat the many-body interactions with quantum Monte Carlo. The effects of U and λ are competitive and the induced transport takes place through different channels. The two mechanisms can be switched by changing the occupation of the dot with a gate voltage.
Scattering matrix approach to non-stationary quantum transport
Moskalets, Michael V
2012-01-01
The aim of this book is to introduce the basic elements of the scattering matrix approach to transport phenomena in dynamical quantum systems of non-interacting electrons. This approach admits a physically clear and transparent description of transport processes in dynamical mesoscopic systems promising basic elements of solid-state devices for quantum information processing. One of the key effects, the quantum pump effect, is considered in detail. In addition, the theory for a recently implemented new dynamical source - injecting electrons with time delay much larger than the electron coherence time - is offered. This theory provides a simple description of quantum circuits with such a single-particle source and shows in an unambiguous way that the tunability inherent to the dynamical systems leads to a number of unexpected but fundamental effects.
Transport properties of a Kondo dot with a larger side-coupled noninteracting quantum dot
International Nuclear Information System (INIS)
Liu, Y S; Fan, X H; Xia, Y J; Yang, X F
2008-01-01
We investigate theoretically linear and nonlinear quantum transport through a smaller quantum dot in a Kondo regime connected to two leads in the presence of a larger side-coupled noninteracting quantum dot, without tunneling coupling to the leads. To do this we employ the slave boson mean field theory with the help of the Keldysh Green's function at zero temperature. The numerical results show that the Kondo conductance peak may develop multiple resonance peaks and multiple zero points in the conductance spectrum owing to constructive and destructive quantum interference effects when the energy levels of the large side-coupled noninteracting dot are located in the vicinity of the Fermi level in the leads. As the coupling strength between two quantum dots increases, the tunneling current through the quantum device as a function of gate voltage applied across the two leads is suppressed. The spin-dependent transport properties of two parallel coupled quantum dots connected to two ferromagnetic leads are also investigated. The numerical results show that, for the parallel configuration, the spin current or linear spin differential conductance are enhanced when the polarization strength in the two leads is increased
Phonon affected transport through molecular quantum
Czech Academy of Sciences Publication Activity Database
Loos, Jan; Koch, T.; Alvermann, A.; Bishop, A. R.; Fehske, H.
2009-01-01
Roč. 21, č. 39 (2009), 395601/1-395601/18 ISSN 0953-8984 Institutional research plan: CEZ:AV0Z10100521 Keywords : quantum dots * electron - phonon interaction * polarons Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.964, year: 2009
Can classical noise enhance quantum transmission?
International Nuclear Information System (INIS)
Wilde, Mark M
2009-01-01
A modified quantum teleportation protocol broadens the scope of the classical forbidden-interval theorems for stochastic resonance. The fidelity measures performance of quantum communication. The sender encodes the two classical bits for quantum teleportation as weak bipolar subthreshold signals and sends them over a noisy classical channel. Two forbidden-interval theorems provide a necessary and sufficient condition for the occurrence of the nonmonotone stochastic resonance effect in the fidelity of quantum teleportation. The condition is that the noise mean must fall outside a forbidden interval related to the detection threshold and signal value. An optimal amount of classical noise benefits quantum communication when the sender transmits weak signals, the receiver detects with a high threshold and the noise mean lies outside the forbidden interval. Theorems and simulations demonstrate that both finite-variance and infinite-variance noise benefit the fidelity of quantum teleportation.
Electron Transport in Quantum Dots and Heat Transport in Molecules
DEFF Research Database (Denmark)
Kirsanskas, Gediminas
to make a device in order to get fundamentally new properties?” [1], or more concretely, when do the quantum effects become important. During the last 30 years, the innovations in fabrication and cooling techniques allowed to produce nanometer scale solid-state or single molecule-based devices...
Theory of quantum transport at nanoscale an introduction
Ryndyk, Dmitry A
2016-01-01
This book is an introduction to a rapidly developing field of modern theoretical physics – the theory of quantum transport at nanoscale. The theoretical methods considered in the book are in the basis of our understanding of charge, spin and heat transport in nanostructures and nanostructured materials and are widely used in nanoelectronics, molecular electronics, spin-dependent electronics (spintronics) and bio-electronics. The book is based on lectures for graduate and post-graduate students at the University of Regensburg and the Technische Universität Dresden (TU Dresden). The first part is devoted to the basic concepts of quantum transport: Landauer-Büttiker method and matrix Green function formalism for coherent transport, Tunneling (Transfer) Hamiltonian and master equation methods for tunneling, Coulomb blockade, vibrons and polarons. The results in this part are obtained as possible without sophisticated techniques, such as nonequilibrium Green functions, which are considered in detail in the...
Transport efficiency in open quantum systems with static and dynamical disorder
Zhang, Yang; Celardo, G. Luca; Borgonovi, Fausto; Kaplan, Lev
2017-12-01
We study, under very general conditions and in a variety of geometries, quantum enhancement of transport in open systems. Both static disorder and dephasing associated with dynamical disorder (or finite temperature) are fully included in the analysis. We show that quantum coherence effects may significantly enhance transport in open quantum systems even in the semiclassical regime (where the decoherence rate is greater than the inter-site hopping amplitude), as long as the static disorder is sufficiently strong. When the strengths of static and dynamical disorder are fixed, there is an optimal opening strength at which the coherent transport enhancement is optimized. Analytic results are obtained in two simple paradigmatic tight-binding models of large systems: the linear chain and the fully connected network. The physical behavior is also reflected, for example, in the FMO photosynthetic complex, which may be viewed as being intermediate between these paradigmatic models. We furthermore show that a nonzero dephasing rate assists transport in an open linear chain when the disorder strength exceeds a critical value, and obtain this critical disorder strength as a function of the degree of opening.
Quantum enhanced estimation of optical detector efficiencies
Directory of Open Access Journals (Sweden)
Barbieri Marco
2016-01-01
Full Text Available Quantum mechanics establishes the ultimate limit to the scaling of the precision on any parameter, by identifying optimal probe states and measurements. While this paradigm is, at least in principle, adequate for the metrology of quantum channels involving the estimation of phase and loss parameters, we show that estimating the loss parameters associated with a quantum channel and a realistic quantum detector are fundamentally different. While Fock states are provably optimal for the former, we identify a crossover in the nature of the optimal probe state for estimating detector imperfections as a function of the loss parameter using Fisher information as a benchmark. We provide theoretical results for on-off and homodyne detectors, the most widely used detectors in quantum photonics technologies, when using Fock states and coherent states as probes.
Hot electrons in superlattices: quantum transport versus Boltzmann equation
DEFF Research Database (Denmark)
Wacker, Andreas; Jauho, Antti-Pekka; Rott, S.
1999-01-01
A self-consistent solution of the transport equation is presented for semiconductor superlattices within different approaches: (i) a full quantum transport model based on nonequilibrium Green functions, (ii) the semiclassical Boltzmann equation for electrons in a miniband, and (iii) Boltzmann...... equation for electrons in Wannier-Stark states. We find good quantitative agreement of the approximations (ii) and (iii) with (i) in their respective ranges of validity. (C) 1999 Elsevier Science B.V. All rights reserved....
What is novel in quantum transport for mesoscopics?
Indian Academy of Sciences (India)
The understanding of mesoscopic transport has now attained an ultimate simplicity. Indeed, orthodox quantum kinetics would seem to say little about mesoscopics that has not been revealed – nearly effortlessly – by more popular means. Such is far from the case, however. The fact that kinetic theory remains very much in ...
Chaotic Dynamics and Transport in Classical and Quantum Systems
International Nuclear Information System (INIS)
2003-01-01
The aim of this summer school is to provide a set of extended and pedagogical lectures, on the major present-day topics in dynamical systems and statistical mechanics including applications. Some articles are dedicated to chaotic transport in plasma turbulence and to quantum chaos. This document gathers the summaries of some presentations
Chaotic Dynamics and Transport in Classical and Quantum Systems
Energy Technology Data Exchange (ETDEWEB)
NONE
2003-07-01
The aim of this summer school is to provide a set of extended and pedagogical lectures, on the major present-day topics in dynamical systems and statistical mechanics including applications. Some articles are dedicated to chaotic transport in plasma turbulence and to quantum chaos. This document gathers the summaries of some presentations.
A transport equation for quantum fields with continuous mass spectrum
International Nuclear Information System (INIS)
Henning, P.A.
1994-02-01
Within a relativistic real-time Green's function formalism, a quantum transport equation for the phase-space distribution function is derived without a quasi-particle approximation. Dissipation is due to a nonzero spectral width, and can be separated into time-local and memory effects. (orig.)
Nonequilibrium transport through molecular junctions in the quantum regime
Czech Academy of Sciences Publication Activity Database
Koch, T.; Loos, Jan; Alvermann, A.; Fehske, H.
2011-01-01
Roč. 84, č. 12 (2011), 125131/1-125131/16 ISSN 1098-0121 Institutional research plan: CEZ:AV0Z10100521 Keywords : theory of electronic transport * scattering mechanisms * polarons and electron-phonon interactions * quantum dots Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.691, year: 2011
Transport through a vibrating quantum dot: Polaronic effects
Czech Academy of Sciences Publication Activity Database
Koch, T.; Loos, Jan; Alvermann, A.; Bishop, A. R.; Fehske, H.
2010-01-01
Roč. 220, č. 1 (2010), 012014/1-012014/9 ISSN 1742-6588 Institutional research plan: CEZ:AV0Z10100521 Keywords : quantum dot, * polaronic effects * low-temperature transport properties Subject RIV: BM - Solid Matter Physics ; Magnetism
Efficient calculation of dissipative quantum transport properties in semiconductor nanostructures
Energy Technology Data Exchange (ETDEWEB)
Greck, Peter
2012-11-26
We present a novel quantum transport method that follows the non-equilibrium Green's function (NEGF) framework but side steps any self-consistent calculation of lesser self-energies by replacing them by a quasi-equilibrium expression. We termed this method the multi-scattering Buettiker-Probe (MSB) method. It generalizes the so-called Buettiker-Probe model but takes into account all relevant individual scattering mechanisms. It is orders of magnitude more efficient than a fully selfconsistent non-equilibrium Green's function calculation for realistic devices, yet accurately reproduces the results of the latter method as well as experimental data. This method is fairly easy to implement and opens the path towards realistic three-dimensional quantum transport calculations. In this work, we review the fundamentals of the non-equilibrium Green's function formalism for quantum transport calculations. Then, we introduce our novel MSB method after briefly reviewing the original Buettiker-Probe model. Finally, we compare the results of the MSB method to NEGF calculations as well as to experimental data. In particular, we calculate quantum transport properties of quantum cascade lasers in the terahertz (THz) and the mid-infrared (MIR) spectral domain. With a device optimization algorithm based upon the MSB method, we propose a novel THz quantum cascade laser design. It uses a two-well period with alternating barrier heights and complete carrier thermalization for the majority of the carriers within each period. We predict THz laser operation for temperatures up to 250 K implying a new temperature record.
Electron Transport in Quantum Dots and Heat Transport in Molecules
DEFF Research Database (Denmark)
Kirsanskas, Gediminas
to make a device in order to get fundamentally new properties?” [1], or more concretely, when do the quantum effects become important. During the last 30 years, the innovations in fabrication and cooling techniques allowed to produce nanometer scale solid-state or single molecule-based devices......, electrically confined electrons in semiconductor nanowires, two dimensional electron gases, carbon nanotubes, or just small metallic particles, nanoscale pieces of semiconductor....
Quantum Transport in Ultra-scaled Junctionless Transistors
Kim, Sunggeun; Luisier, Mathieu; Klimeck, Gerhard
2012-02-01
As the dimensions of metal-oxide-semiconductor field-effect transistors have been scaled down to a few nano-meters, short channel effects have started to significantly degrade their performance. The junctionless transistor is an alternative device structure which is expected to reduce short channel effects. However, an extreme device scaling raises another issue, namely, source-to-drain tunneling. Junctionless transistors contain several doping atoms in the channel which can enhance tunneling processes and cause electrons to scatter with them. Through self-consistent quantum transport simulations based on the tight-binding model with elelctron-phonon scattering included, it is found that junctionless nanowire transistors with a gate length of 5 nm do not outperform conventional inversion-mode transistors with the same dimension in terms of their on-state characteristics, mainly due to impurity scattering in the channel. The advantage of the junctionless transistor in the the subthreshold region vanishes due to large tunneling currents through doping impurities.
Optimal tunneling enhances the quantum photovoltaic effect in double quantum dots
International Nuclear Information System (INIS)
Wang, Chen; Cao, Jianshu; Ren, Jie
2014-01-01
We investigate the quantum photovoltaic effect in double quantum dots by applying the nonequilibrium quantum master equation. A drastic suppression of the photovoltaic current is observed near the open circuit voltage, which leads to a large filling factor. We find that there always exists an optimal inter-dot tunneling that significantly enhances the photovoltaic current. Maximal output power will also be obtained around the optimal inter-dot tunneling. Moreover, the open circuit voltage behaves approximately as the product of the eigen-level gap and the Carnot efficiency. These results suggest a great potential for double quantum dots as efficient photovoltaic devices
Frictional lubricity enhanced by quantum mechanics.
Zanca, Tommaso; Pellegrini, Franco; Santoro, Giuseppe E; Tosatti, Erio
2018-03-19
The quantum motion of nuclei, generally ignored in the physics of sliding friction, can affect in an important manner the frictional dissipation of a light particle forced to slide in an optical lattice. The density matrix-calculated evolution of the quantum version of the basic Prandtl-Tomlinson model, describing the dragging by an external force of a point particle in a periodic potential, shows that purely classical friction predictions can be very wrong. The strongest quantum effect occurs not for weak but for strong periodic potentials, where barriers are high but energy levels in each well are discrete, and resonant Rabi or Landau-Zener tunneling to states in the nearest well can preempt classical stick-slip with nonnegligible efficiency, depending on the forcing speed. The resulting permeation of otherwise unsurmountable barriers is predicted to cause quantum lubricity, a phenomenon which we expect should be observable in the recently implemented sliding cold ion experiments.
Computing and the electrical transport properties of coupled quantum networks
Cain, Casey Andrew
In this dissertation a number of investigations were conducted on ballistic quantum networks in the mesoscopic range. In this regime, the wave nature of electron transport under the influence of transverse magnetic fields leads to interesting applications for digital logic and computing circuits. The work specifically looks at characterizing a few main areas that would be of interest to experimentalists who are working in nanostructure devices, and is organized as a series of papers. The first paper analyzes scaling relations and normal mode charge distributions for such circuits in both isolated and open (terminals attached) form. The second paper compares the flux-qubit nature of quantum networks to the well-established spintronics theory. The results found exactly contradict the conventional school of thought for what is required for quantum computation. The third paper investigates the requirements and limitations of extending the Thevenin theorem in classic electric circuits to ballistic quantum transport. The fourth paper outlines the optimal functionally complete set of quantum circuits that can completely satisfy all sixteen Boolean logic operations for two variables.
Coherence enhanced quantum metrology in a nonequilibrium optical molecule
Wang, Zhihai; Wu, Wei; Cui, Guodong; Wang, Jin
2018-03-01
We explore the quantum metrology in an optical molecular system coupled to two environments with different temperatures, using a quantum master equation beyond secular approximation. We discover that the steady-state coherence originating from and sustained by the nonequilibrium condition can enhance quantum metrology. We also study the quantitative measures of the nonequilibrium condition in terms of the curl flux, heat current and entropy production at the steady state. They are found to grow with temperature difference. However, an apparent paradox arises considering the contrary behaviors of the steady-state coherence and the nonequilibrium measures in relation to the inter-cavity coupling strength. This paradox is resolved by decomposing the heat current into a population part and a coherence part. Only the latter, the coherence part of the heat current, is tightly connected to the steady-state coherence and behaves similarly with respect to the inter-cavity coupling strength. Interestingly, the coherence part of the heat current flows from the low-temperature reservoir to the high-temperature reservoir, opposite to the direction of the population heat current. Our work offers a viable way to enhance quantum metrology for open quantum systems through steady-state coherence sustained by the nonequilibrium condition, which can be controlled and manipulated to maximize its utility. The potential applications go beyond quantum metrology and extend to areas such as device designing, quantum computation and quantum technology in general.
Fractional quantum mechanics on networks: Long-range dynamics and quantum transport.
Riascos, A P; Mateos, José L
2015-11-01
In this paper we study the quantum transport on networks with a temporal evolution governed by the fractional Schrödinger equation. We generalize the dynamics based on continuous-time quantum walks, with transitions to nearest neighbors on the network, to the fractional case that allows long-range displacements. By using the fractional Laplacian matrix of a network, we establish a formalism that combines a long-range dynamics with the quantum superposition of states; this general approach applies to any type of connected undirected networks, including regular, random, and complex networks, and can be implemented from the spectral properties of the Laplacian matrix. We study the fractional dynamics and its capacity to explore the network by means of the transition probability, the average probability of return, and global quantities that characterize the efficiency of this quantum process. As a particular case, we explore analytically these quantities for circulant networks such as rings, interacting cycles, and complete graphs.
Disorder-Enhanced Transport in Photonic Quasicrystals
Levi, Liad; Rechtsman, Mikael; Freedman, Barak; Schwartz, Tal; Manela, Ofer; Segev, Mordechai
2011-06-01
Quasicrystals are aperiodic structures with rotational symmetries forbidden to conventional periodic crystals; examples of quasicrystals can be found in aluminum alloys, polymers, and even ancient Islamic art. Here, we present direct experimental observation of disorder-enhanced wave transport in quasicrystals, which contrasts directly with the characteristic suppression of transport by disorder. Our experiments are carried out in photonic quasicrystals, where we find that increasing disorder leads to enhanced expansion of the beam propagating through the medium. By further increasing the disorder, we observe that the beam progresses through a regime of diffusive-like transport until it finally transitions to Anderson localization and the suppression of transport. We study this fundamental phenomenon and elucidate its origins by relating it to the basic properties of quasicrystalline media in the presence of disorder.
Quantum Dot Spectrum Converters for Enhanced High Efficiency Photovoltaics, Phase I
National Aeronautics and Space Administration — This research proposes to enhance solar cell efficiency, radiation resistance and affordability. The Quantum Dot Spectrum Converter (QDSC) disperses quantum dots...
Detecting monopole charge in Weyl semimetals via quantum interference transport
Dai, Xin; Lu, Hai-Zhou; Shen, Shun-Qing; Yao, Hong
2016-04-01
Topological Weyl semimetals can host Weyl nodes with monopole charges in momentum space. How to detect the signature of the monopole charges in quantum transport remains a challenging topic. Here, we reveal the connection between the parity of monopole charge in topological semimetals and the quantum interference corrections to the conductivity. We show that the parity of monopole charge determines the sign of the quantum interference correction, with odd and even parity yielding the weak antilocalization and weak localization effects, respectively. This is attributed to the Berry phase difference between time-reversed trajectories circulating the Fermi sphere that encloses the monopole charges. From standard Feynman diagram calculations, we further show that the weak-field magnetoconductivity at low temperatures is proportional to +√{B } in double-Weyl semimetals and -√{B } in single-Weyl semimetals, respectively, which could be verified experimentally.
Spin-orbit-enhanced Wigner localization in quantum dots
DEFF Research Database (Denmark)
Cavalli, Andrea; Malet, F.; Cremon, J. C.
2011-01-01
We investigate quantum dots with Rashba spin-orbit coupling in the strongly-correlated regime. We show that the presence of the Rashba interaction enhances the Wigner localization in these systems, making it achievable for higher densities than those at which it is observed in Rashba-free quantum...... dots. Recurring shapes in the pair distribution functions of the yrast spectrum, which might be associated with rotational and vibrational modes, are also reported....
Enhanced thermoelectric response in the fractional quantum Hall effect
Roura-Bas, Pablo; Arrachea, Liliana; Fradkin, Eduardo
2018-02-01
We study the linear thermoelectric response of a quantum dot embedded in a constriction of a quantum Hall bar with fractional filling factors ν =1 /m within Laughlin series. We calculate the figure of merit Z T for the maximum efficiency at a fixed temperature difference. We find a significant enhancement of this quantity in the fractional filling in relation to the integer-filling case, which is a direct consequence of the fractionalization of the electron in the fractional quantum Hall state. We present simple theoretical expressions for the Onsager coefficients at low temperatures, which explicitly show that Z T and the Seebeck coefficient increase with m .
Currents and fluctuations of quantum heat transport in harmonic chains
International Nuclear Information System (INIS)
Motz, T; Ankerhold, J; Stockburger, J T
2017-01-01
Heat transport in open quantum systems is particularly susceptible to the modeling of system–reservoir interactions. It thus requires us to consistently treat the coupling between a quantum system and its environment. While perturbative approaches are successfully used in fields like quantum optics and quantum information, they reveal deficiencies—typically in the context of thermodynamics, when it is essential to respect additional criteria such as fluctuation-dissipation theorems. We use a non-perturbative approach for quantum dissipative dynamics based on a stochastic Liouville–von Neumann equation to provide a very general and extremely efficient formalism for heat currents and their correlations in open harmonic chains. Specific results are derived not only for first- but also for second-order moments, which requires us to account for both real and imaginary parts of bath–bath correlation functions. Spatiotemporal patterns are compared with weak coupling calculations. The regime of stronger system–reservoir couplings gives rise to an intimate interplay between reservoir fluctuations and heat transfer far from equilibrium. (paper)
Currents and fluctuations of quantum heat transport in harmonic chains
Motz, T.; Ankerhold, J.; Stockburger, J. T.
2017-05-01
Heat transport in open quantum systems is particularly susceptible to the modeling of system-reservoir interactions. It thus requires us to consistently treat the coupling between a quantum system and its environment. While perturbative approaches are successfully used in fields like quantum optics and quantum information, they reveal deficiencies—typically in the context of thermodynamics, when it is essential to respect additional criteria such as fluctuation-dissipation theorems. We use a non-perturbative approach for quantum dissipative dynamics based on a stochastic Liouville-von Neumann equation to provide a very general and extremely efficient formalism for heat currents and their correlations in open harmonic chains. Specific results are derived not only for first- but also for second-order moments, which requires us to account for both real and imaginary parts of bath-bath correlation functions. Spatiotemporal patterns are compared with weak coupling calculations. The regime of stronger system-reservoir couplings gives rise to an intimate interplay between reservoir fluctuations and heat transfer far from equilibrium.
The Landauer-Büttiker formula and resonant quantum transport
DEFF Research Database (Denmark)
Cornean, Horia; Jensen, Arne; Moldoveanu, Valeriu
2006-01-01
We give a short presentation of two recent results. The first one is a rigorous proof of the Landauer-Büttiker formula, and the second one concerns resonant quantum transport. The detailed results are in [2]. In the last section we present the results of som numerical computations on a model system....... Concerning the literature, then see the starting point of our work [6]. In [4] a related, but different, problem is studied. See also [5] and the recent work [1]....
The Landauer-Büttiker formula and resonant quantum transport
DEFF Research Database (Denmark)
Cornean, Horia Decebal; Jensen, Arne; Moldoveanu, Valeriu
We give a short presentation of two recent results. The firrst one is a rigorous proof of the Landauer-Büttiker formula, and the second one concerns resonant quantum transport. The detailed results are in [2]. In the last section we present the results of some numerical computations on a model...... system.Concerning the literature, then see the starting point of our work, [6]. In [4] a related, but different, problem is studied. See also [5] and the recentwork [1]....
Enhancing quantum annealing performance for the molecular similarity problem
Hernandez, Maritza; Aramon, Maliheh
2017-05-01
Quantum annealing is a promising technique which leverages quantum mechanics to solve hard optimization problems. Considerable progress has been made in the development of a physical quantum annealer, motivating the study of methods to enhance the efficiency of such a solver. In this work, we present a quantum annealing approach to measure similarity among molecular structures. Implementing real-world problems on a quantum annealer is challenging due to hardware limitations such as sparse connectivity, intrinsic control error, and limited precision. In order to overcome the limited connectivity, a problem must be reformulated using minor-embedding techniques. Using a real data set, we investigate the performance of a quantum annealer in solving the molecular similarity problem. We provide experimental evidence that common practices for embedding can be replaced by new alternatives which mitigate some of the hardware limitations and enhance its performance. Common practices for embedding include minimizing either the number of qubits or the chain length and determining the strength of ferromagnetic couplers empirically. We show that current criteria for selecting an embedding do not improve the hardware's performance for the molecular similarity problem. Furthermore, we use a theoretical approach to determine the strength of ferromagnetic couplers. Such an approach removes the computational burden of the current empirical approaches and also results in hardware solutions that can benefit from simple local classical improvement. Although our results are limited to the problems considered here, they can be generalized to guide future benchmarking studies.
Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles
International Nuclear Information System (INIS)
Iida, Daisuke; Fadil, Ahmed; Ou, Yiyu; Kopylov, Oleksii; Ou, Haiyan; Chen, Yuntian; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu
2015-01-01
We report internal quantum efficiency enhancement of thin p-GaN green quantum-well structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density on the enhancement factor is investigated. We obtain an internal quantum efficiency enhancement by a factor of 2.3 at 756 W/cm 2 , and a factor of 8.1 at 1 W/cm 2 . A Purcell enhancement up to a factor of 26 is estimated by fitting the experimental results to a theoretical model for the efficiency enhancement factor
Enhanced transport of relativistic electrons through nanochannels
Directory of Open Access Journals (Sweden)
Prashant Kumar Singh
2013-06-01
Full Text Available Efficient transport of fast electrons driven by intense laser solid interaction depends crucially on optimal target design. We demonstrate a hybrid target design that incorporates two important features—efficient generation of relativistic electrons and their unimpeded transport in dense media. The target was fabricated on a porous alumina base consisting of an array of sublambda cylindrical holes partially filled with Cu nanorods, such that light field propagates in the hollow channels, located ahead of the metallic fillings. The hollow array acts as an efficient source of hot electrons when driven by relativistically intense, femtosecond laser pulses and shows a 60-fold enhancement in electron flux compared to a solid target. This enhancement is ascribed to an increased penetration of laser through subwavelength pores and enhanced local electric fields. The metal doped part facilitates efficient transport of the generated electrons, due to its large background conductivity. A 4-fold enhancement in target rear side electron flux is observed compared with unfilled porous alumina.
Quasiparticle transport and induced superconductivity in InAs-AlSb quantum wells with Nb electrodes
International Nuclear Information System (INIS)
Kroemer, H.; Nguyen, C.; Hu, E.L.; Yuh, E.L.; Thomas, M.; Wong, K.C.
1994-01-01
Current transport through InAs-AlSb quantum wells contacted with superconducting Nb electrodes shows strong evidence for the presence of multiple Andreev reflections (AR's). The efficiency of the multiple AR process is greatly enhanced by the specular normal reflection of electrons at the backplane of the quantum well, thereby permitting multiple AR attempts. Superconductivity observed for sufficiently narrow inter-electrode gaps is interpreted as the result of phase-coherent multiple AR's.Series-connected multi-junction InAs-Nb arrays have been constructed by contacting the InAs-AlSb quantum well with a periodic grating of superconducting Nb electrodes with sub-micrometer spacings. They showed superconductivity at sufficiently low temperatures, in one case as high as 4.2 K. Above the transition temperatures, strong precursors of the superconductivity were observed, in the form of dramatically enhanced zero-bias conductances, decreasing with increasing temperature, but larger by about a factor on the order 10 4 than the fluctuation-induced precursors of thin BCS films. Weak magnetic fields restored non-zero resistance values; the increase in resistance with increasing magnetic field contained a component periodic in the magnetic field, with a period corresponding to a flux per grating cell of only a fraction (∼(1)/(5)-(1)/(2)) of a conventional flux quantum. The observations are interpreted in terms of the formation of a flux cell superlattice. ((orig.))
Electron transport in InAs/AlSb quantum wells
International Nuclear Information System (INIS)
Tuttle, G.; Kroemer, H.; English, J.H.
1989-01-01
The authors present data on electron transport in AlSb/InAs/AlSb quantum wells grown by molecular beam epitaxy. Because both anion and cation change across an InAs/Alsb interface, it is possible to grow such wells with two different types of interfaces, one with an InSb-like bond configuration, the other AlAs-like. Electron mobility and concentration were found to depend very strongly on the manner in which the quantum well's interfaces were grown, with high mobilities seen only if the bottom interface is InSb-like. An As-on-Al sites antisite defect model is postulated for bottom AlAs-like interfaces
Non-Markovian dynamics of quantum systems: formalism, transport coefficients
International Nuclear Information System (INIS)
Kanokov, Z.; Palchikov, Yu.V.; Antonenko, N.V.; Adamian, G.G.; Kanokov, Z.; Adamian, G.G.; Scheid, W.
2004-01-01
Full text: The generalized Linbland equations with non-stationary transport coefficients are derived from the Langevin equations for the case of nonlinear non-Markovian noise [1]. The equations of motion for the collective coordinates are consistent with the generalized quantum fluctuation dissipation relations. The microscopic justification of the Linbland axiomatic approach is performed. Explicit expressions for the time-dependent transport coefficients are presented for the case of FC- and RWA-oscillators and a general linear coupling in coordinate and in momentum between the collective subsystem and heat bath. The explicit equations for the correlation functions show that the Onsanger's regression hypothesis does not hold exactly for the non-Markovian equations of motion. However, under some conditions the regression of fluctuations goes to zero in the same manner as the average values. In the low and high temperature regimes we found that the dissipation leads to long-time tails in correlation functions in the RWA-oscillator. In the case of the FC-oscillator a non-exponential power-like decay of the correlation function in coordinate is only obtained only at the low temperature limit. The calculated results depend rather weakly on the memory time in many applications. The found transient times for diffusion coefficients D pp (t), D qp (t) and D qq (t) are quite short. The value of classical diffusion coefficients in momentum underestimates the asymptotic value of quantum one D pp (t), but the asymptotic values of classical σ qq c and quantum σ qq second moments are close due to the negativity of quantum mixed diffusion coefficient D qp (t)
Quantum dot transport in soil, plants, and insects
Energy Technology Data Exchange (ETDEWEB)
Al-Salim, Najeh [Industrial Research Ltd, P.O. Box 31310, Lower Hutt 5040 (New Zealand); Barraclough, Emma; Burgess, Elisabeth [New Zealand Institute for Plant and Food Research Ltd, Private Bag 92169, Victoria Street West, Auckland 1142 (New Zealand); Clothier, Brent, E-mail: brent.clothier@plantandfood.co.nz [New Zealand Institute for Plant and Food Research Ltd, Private Bag 11600, Manawatu Mail Centre, Palmerston North 4442 (New Zealand); Deurer, Markus; Green, Steve [New Zealand Institute for Plant and Food Research Ltd, Private Bag 11600, Manawatu Mail Centre, Palmerston North 4442 (New Zealand); Malone, Louise [New Zealand Institute for Plant and Food Research Ltd, Private Bag 92169, Victoria Street West, Auckland 1142 (New Zealand); Weir, Graham [Industrial Research Ltd, P.O. Box 31310, Lower Hutt 5040 (New Zealand)
2011-08-01
Environmental risk assessment of nanomaterials requires information not only on their toxicity to non-target organisms, but also on their potential exposure pathways. Here we report on the transport and fate of quantum dots (QDs) in the total environment: from soils, through their uptake into plants, to their passage through insects following ingestion. Our QDs are nanoparticles with an average particle size of 6.5 nm. Breakthrough curves obtained with CdTe/mercaptopropionic acid QDs applied to columns of top soil from a New Zealand organic apple orchard, a Hastings silt loam, showed there to be preferential flow through the soil's macropores. Yet the effluent recovery of QDs was just 60%, even after several pore volumes, indicating that about 40% of the influent QDs were filtered and retained by the soil column via some unknown exchange/adsorption/sequestration mechanism. Glycine-, mercaptosuccinic acid-, cysteine-, and amine-conjugated CdSe/ZnS QDs were visibly transported to a limited extent in the vasculature of ryegrass (Lolium perenne), onion (Allium cepa) and chrysanthemum (Chrysanthemum sp.) plants when cut stems were placed in aqueous QD solutions. However, they were not seen to be taken up at all by rooted whole plants of ryegrass, onion, or Arabidopsis thaliana placed in these solutions. Leafroller (Lepidoptera: Tortricidae) larvae fed with these QDs for two or four days, showed fluorescence along the entire gut, in their frass (larval feces), and, at a lower intensity, in their haemolymph. Fluorescent QDs were also observed and elevated cadmium levels detected inside the bodies of adult moths that had been fed QDs as larvae. These results suggest that exposure scenarios for QDs in the total environment could be quite complex and variable in each environmental domain. - Research highlights: {yields} Quantum dots are transported rapidly through soil but half were retained. {yields} Intact roots of plants did not take up quantum dots. Excised plants
On Parallel Transport in Quantum Bundles over Robertson-Walker Spacetimes
Coleman, James
1996-01-01
A recently-developed theory of quantum general relativity provides a propagator for free-falling particles in curved spacetimes. These propagators are constructed by parallel-transporting quantum states within a quantum bundle associated to the Poincare frame bundle. We consider such parallel transport in the case that the spacetime is a classical Robertson-Walker universe. An explicit integral formula is developed which expresses the propagators for parallel transport between any two points ...
Quantum transport through ballistic chaotic cavities: a statistical approach
International Nuclear Information System (INIS)
Mello, P.A.
1998-01-01
The problem of quantum chaotic scattering is addressed by means of a statistical model for the scattering matrix. The model, introduced in the past in the context of nuclear physics, describes the problem in terms of a prompt and an equilibrated component: it incorporates the average value of the scattering matrix to describe the prompt processes and satisfies the requirements of flux conservation, causality and ergodicity. The model is applied to the analysis of electronic transport through ballistic mesoscopic cavities: it describes well the results arising form the numerical solution of the Schroedinger equation for two-dimensional cavities. (Author)
Cavity-Enhanced Transport of Charge
Hagenmüller, David; Schachenmayer, Johannes; Schütz, Stefan; Genes, Claudiu; Pupillo, Guido
2017-12-01
We theoretically investigate charge transport through electronic bands of a mesoscopic one-dimensional system, where interband transitions are coupled to a confined cavity mode, initially prepared close to its vacuum. This coupling leads to light-matter hybridization where the dressed fermionic bands interact via absorption and emission of dressed cavity photons. Using a self-consistent nonequilibrium Green's function method, we compute electronic transmissions and cavity photon spectra and demonstrate how light-matter coupling can lead to an enhancement of charge conductivity in the steady state. We find that depending on cavity loss rate, electronic bandwidth, and coupling strength, the dynamics involves either an individual or a collective response of Bloch states, and we explain how this affects the current enhancement. We show that the charge conductivity enhancement can reach orders of magnitudes under experimentally relevant conditions.
Chiral heat transport in driven quantum Hall and quantum spin Hall edge states
Arrachea, Liliana; Fradkin, Eduardo
2011-12-01
We consider a model for an edge state of electronic systems in the quantum Hall regime with filling ν=1 and in the quantum spin Hall regime. In both cases, the system is in contact with two reservoirs by tunneling at point contacts. Both systems are locally driven by applying an ac voltage in one of the contacts. By weakly coupling them to a third reservoir, the transport of the generated heat is studied in two different ways: (i) when the third reservoir acts as a thermometer, the local temperature is sensed and (ii) when the third reservoir acts as a voltage probe, the time-dependent local voltage is sensed. Our results indicate a chiral propagation of the heat along the edge in the quantum Hall and in the quantum spin Hall cases (if the injected electrons are spin polarized). We also show that a analogous picture is obtained if instead of heating by ac driving the system is put in contact to a stationary reservoir at a higher temperature. In both cases, the temperature profile shows that the electrons along the edge thermalize with the closest “upstream” reservoir.
Non-adiabatic quantum state preparation and quantum state transport in chains of Rydberg atoms
Ostmann, Maike; Minář, Jiří; Marcuzzi, Matteo; Levi, Emanuele; Lesanovsky, Igor
2017-12-01
Motivated by recent progress in the experimental manipulation of cold atoms in optical lattices, we study three different protocols for non-adiabatic quantum state preparation and state transport in chains of Rydberg atoms. The protocols we discuss are based on the blockade mechanism between atoms which, when excited to a Rydberg state, interact through a van der Waals potential, and rely on single-site addressing. Specifically, we discuss protocols for efficient creation of an antiferromagnetic GHZ state, a class of matrix product states including a so-called Rydberg crystal and for the state transport of a single-qubit quantum state between two ends of a chain of atoms. We identify system parameters allowing for the operation of the protocols on timescales shorter than the lifetime of the Rydberg states while yielding high fidelity output states. We discuss the effect of positional disorder on the resulting states and comment on limitations due to other sources of noise such as radiative decay of the Rydberg states. The proposed protocols provide a testbed for benchmarking the performance of quantum information processing platforms based on Rydberg atoms.
Dark states in spin-polarized transport through triple quantum dot molecules
Wrześniewski, K.; Weymann, I.
2018-02-01
We study the spin-polarized transport through a triple-quantum-dot molecule weakly coupled to ferromagnetic leads. The analysis is performed by means of the real-time diagrammatic technique, including up to the second order of perturbation expansion with respect to the tunnel coupling. The emphasis is put on the impact of dark states on spin-resolved transport characteristics. It is shown that the interplay of coherent population trapping and cotunneling processes results in a highly nontrivial behavior of the tunnel magnetoresistance, which can take negative values. Moreover, a super-Poissonian shot noise is found in transport regimes where the current is blocked by the formation of dark states, which can be additionally enhanced by spin dependence of tunneling processes, depending on the magnetic configuration of the device. The mechanisms leading to those effects are thoroughly discussed.
Transport Properties of the Nuclear Pasta Phase with Quantum Molecular Dynamics
Nandi, Rana; Schramm, Stefan
2018-01-01
We study the transport properties of nuclear pasta for a wide range of density, temperature, and proton fractions, relevant for different astrophysical scenarios adopting a quantum molecular dynamics model. In particular, we estimate the values of shear viscosity as well as electrical and thermal conductivities by calculating the static structure factor S(q) using simulation data. In the density and temperature range where the pasta phase appears, the static structure factor shows irregular behavior. The presence of a slab phase greatly enhances the peak in S(q). However, the effect of irregularities in S(q) on the transport coefficients is not very dramatic. The values of all three transport coefficients are found to have the same orders of magnitude as found in theoretical calculations for the inner crust matter of neutron stars without the pasta phase; therefore, the values are in contrast to earlier speculations that a pasta layer might be highly resistive, both thermally and electrically.
Thermal transport in out-of-equilibrium quantum harmonic chains.
Nicacio, F; Ferraro, A; Imparato, A; Paternostro, M; Semião, F L
2015-04-01
We address the problem of heat transport in a chain of coupled quantum harmonic oscillators, exposed to the influences of local environments of various nature, stressing the effects that the specific nature of the environment has on the phenomenology of the transport process. We study in detail the behavior of thermodynamically relevant quantities such as heat currents and mean energies of the oscillators, establishing rigorous analytical conditions for the existence of a steady state, whose features we analyze carefully. In particular, we assess the conditions that should be faced to recover trends reminiscent of the classical Fourier law of heat conduction and highlight how such a possibility depends on the environment linked to our system.
Labeling of Neuronal Receptors and Transporters with Quantum Dots
Chang, Jerry C.; Kovtun, Oleg; Blakely, Randy D.; Rosenthal, Sandra J.
2012-01-01
The ability to efficiently visualize protein targets in cells is a fundamental goal in biological research. Recently, quantum dots (QDots) have emerged as a powerful class of fluorescent probes for labeling membrane proteins in living cells due to breakthrough advances in QDot surface chemistry and biofunctionalization strategies. This review discusses the increasing use of QDots for fluorescence imaging of neuronal receptors and transporters. The readers are briefly introduced to QDot structure, photophysical properties, and common synthetic routes towards the generation of water-soluble QDots. The next section highlights several reports of QDot application that seek to unravel molecular aspects of neuronal receptor and transporter regulation and trafficking. We close with a prospectus of the future of derivatized QDots in neurobiological and pharmacological research. PMID:22887823
Directed transport in classical and quantum chaotic billiards
Energy Technology Data Exchange (ETDEWEB)
Acevedo, W; Dittrich, T [Departamento de Fisica, Universidad Nacional de Colombia, and CeiBA, Complejidad, Bogota DC (Colombia)], E-mail: jwacevedov@unal.edu.co, E-mail: tdittrich@unal.edu.co
2009-01-30
We construct an autonomous chaotic Hamiltonian ratchet as a channel billiard subdivided by equidistant walls attached perpendicularly to one side of the channel, leaving an opening on the opposite side. A static homogeneous magnetic field penetrating the billiard breaks time-reversal invariance and renders the classical motion partially chaotic. We show that the classical dynamics exhibits directed transport, owing to the asymmetric distribution of regular regions in phase space. The billiard is quantized by a numerical method based on a finite-element algorithm combined with the Landau gauge and the Bloch formalism for periodic potentials. We discuss features of the billiard eigenstates such as node lines and vortices in the probability flow. Evidence for directed quantum transport, inherited from the corresponding features of the classical dynamics, is presented in terms of level-velocity statistics.
Opto-electronic and quantum transport properties of semiconductor nanostructures
Energy Technology Data Exchange (ETDEWEB)
Sabathil, M.
2005-01-01
In this work a novel and efficient method for the calculation of the ballistic transport properties of open semiconductor nanostructures connected to external reservoirs is presented. It is based on the Green's function formalism and reduces the effort to obtain the transmission and the carrier density to a single solution of a hermitian eigenvalue problem with dimensions proportional to the size of the decoupled device and the multiple inversion of a small matrix with dimensions proportional to the size of the contacts to the leads. Using this method, the 4-band GaAs hole transport through a 2-dimensional three-terminal T-junction device, and the resonant tunneling current through a 3-dimensional InAs quantum dot molecule embedded into an InP heterostructure have been calculated. The further extension of the method into a charge self-consistent scheme enables the efficient prediction of the IV-characteristics of highly doped nanoscale field effect transistors in the ballistic regime, including the influence of quasi bound states and the exchange-correlation interaction. Buettiker probes are used to emulate the effect of inelastic scattering on the current for simple 1D devices, systematically analyzing the dependence of the density of states and the resulting self-consistent potential on the scattering strength. The second major topic of this work is the modeling of the optical response of quantum confined neutral and charged excitons in single and coupled self-assembled InGaAs quantum dots. For this purpose the existing device simulator nextnano{sup 3} has been extended to incorporate particle-particle interactions within the means of density functional theory in local density approximation. In this way the exciton transition energies for neutral and charged excitons as a function of an externally applied electric field have been calculated, revealing a systematic reduction of the intrinsic dipole with the addition of extra holes to the exciton, a finding
Novel phenomena in one-dimensional non-linear transport in long quantum wires
International Nuclear Information System (INIS)
Morimoto, T; Hemmi, M; Naito, R; Tsubaki, K; Park, J-S; Aoki, N; Bird, J P; Ochiai, Y
2006-01-01
We have investigated the non-linear transport properties of split-gate quantum wires of various channel lengths. In this report, we present results on a resonant enhancement of the non-linear conductance that is observed near pinch-off under a finite source-drain bias voltage. The resonant phenomenon exhibits a strong dependence on temperature and in-plane magnetic field. We discuss the possible relationship of this phenomenon to the spin-polarized manybody state that has recently been suggested to occur in quasi-one dimensional systems
Photon-number correlation for quantum enhanced imaging and sensing
Meda, A.; Losero, E.; Samantaray, N.; Scafirimuto, F.; Pradyumna, S.; Avella, A.; Ruo-Berchera, I.; Genovese, M.
2017-09-01
In this review we present the potentialities and the achievements of the use of non-classical photon-number correlations in twin-beam states for many applications, ranging from imaging to metrology. Photon-number correlations in the quantum regime are easily produced and are rather robust against unavoidable experimental losses, and noise in some cases, if compared to the entanglement, where losing one photon can completely compromise the state and its exploitable advantages. Here, we will focus on quantum enhanced protocols in which only phase-insensitive intensity measurements (photon-number counting) are performed, which allow probing the transmission/absorption properties of a system, leading, for example, to innovative target detection schemes in a strong background. In this framework, one of the advantages is that the sources experimentally available emit a wide number of pair-wise correlated modes, which can be intercepted and exploited separately, for example by many pixels of a camera, providing a parallelism, essential in several applications, such as wide-field sub-shot-noise imaging and quantum enhanced ghost imaging. Finally, non-classical correlation enables new possibilities in quantum radiometry, e.g. the possibility of absolute calibration of a spatial resolving detector from the on-off single-photon regime to the linear regime in the same setup.
Energy Technology Data Exchange (ETDEWEB)
Li, Tian, E-mail: tianlee@umd.edu, E-mail: dage@ece.umd.edu; Dagenais, Mario, E-mail: tianlee@umd.edu, E-mail: dage@ece.umd.edu [Department of Electrical Engineering, University of Maryland, College Park, Maryland 20742 (United States); Lu, Haofeng; Fu, Lan; Tan, Hark Hoe; Jagadish, Chennupati [Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra ACT 0200 (Australia)
2015-02-02
Reduced quantum dot (QD) absorption due to state filling effects and enhanced electron transport in doped QDs are demonstrated to play a key role in solar energy conversion. Reduced QD state absorption with increased n-doping is observed in the self-assembled In{sub 0.5}Ga{sub 0.5}As/GaAs QDs from high resolution below-bandgap external quantum efficiency (EQE) measurement, which is a direct consequence of the Pauli exclusion principle. We also show that besides partial filling of the quantum states, electron-doping produces negatively charged QDs that exert a repulsive Coulomb force on the mobile electrons, thus altering the electron trajectory and reducing the probability of electron capture, leading to an improved collection efficiency of photo-generated carriers, as indicated by an absolute above-bandgap EQE measurement. The resulting redistribution of the mobile electron in the planar direction is further validated by the observed photoluminescence intensity dependence on doping.
Graded Doping for Enhanced Colloidal Quantum Dot Photovoltaics
Ning, Zhijun
2013-02-05
A novel approach to improving all-inorganic colloidal quantum dot (CQD) homojunction solar cells by engineering the doping spatial profile to produce a doping gradient within the n-type absorber is presented. The doping gradient greatly improves carrier collection and enhances the voltages attainable by the device, leading to a 1 power point power conversion efficiency (PCE) improvement over previous inorganic CQD solar cells. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Maiti, Buddhadev; Schubert, Alexander; Sarkar, Sunandan; Bhandari, Srijana; Wang, Kunlun; Li, Zhe; Geva, Eitan; Twieg, Robert J; Dunietz, Barry D
2017-10-01
Selective fluorination of organic semiconducting molecules is proposed as a means to achieving enhanced hole mobility. Naphthalene is examined here as a root molecular system with fluorination performed at various sites. Our quantum chemical calculations show that selective fluorination can enhance attractive intermolecular interactions while reducing charge trapping. Those observations suggest a design principle whereby fluorination is utilized for achieving high charge mobilities in the crystalline form. The utility of this design principle is demonstrated through an application to perylene, which is an important building block of organic semiconducting materials. We also show that a quantum mechanical perspective of nuclear degrees of freedom is crucial for a reliable description of charge transport.
Quantum transport through mesoscopic disordered interfaces, junctions, and multilayers
International Nuclear Information System (INIS)
Nikolic, Branislav K.
2002-01-01
This study explores perpendicular transport through macroscopically inhomogeneous three-dimensional disordered conductors using mesoscopic methods (the real-space Green function technique in a two-probe measuring geometry). The nanoscale samples (containing ∼ 1000 atoms) are modelled by a tight-binding Hamiltonian on a simple cubic lattice where disorder is introduced in the on-site potential energy. I compute the transport properties of: disordered metallic junctions formed by concatenating two homogeneous samples with different kinds of microscopic disorder, a single strongly disordered interface, and multilayers composed of such interfaces and homogeneous layers characterized by different strengths of the same type of microscopic disorder. This allows us to: contrast the resistor model (semiclassical) approach with a fully quantum description of dirty mesoscopic multilayers; study the transmission properties of dirty interfaces (where the Schep-Bauer distribution of transmission eigenvalues is confirmed for a single interface, as well as for a stack of such interfaces that is thinner than the localization length); and elucidate the effect of coupling to ideal leads ('measuring apparatus') on the conductance of both bulk conductors and dirty interfaces. When a multilayer contains a ballistic layer in between two interfaces, its disorder-averaged conductance oscillates as a function of the Fermi energy. I also address some fundamental issues in quantum transport theory - the relationship between the Kubo formula in the exact state representation and the 'mesoscopic Kubo formula' (which gives the exact zero-temperature conductance of a finite-size sample attached to two semi-infinite ideal leads) is thoroughly re-examined by comparing their outcomes for both the junctions and homogeneous samples. (author)
Quantum transport in nanowire-based hybrid devices
Energy Technology Data Exchange (ETDEWEB)
Guenel, Haci Yusuf
2013-05-08
We have studied the low-temperature transport properties of nanowires contacted by a normal metal as well as by superconducting electrodes. As a consequence of quantum coherence, we have demonstrated the electron interference effect in different aspects. The mesoscopic phase coherent transport properties were studied by contacting the semiconductor InAs and InSb nanowires with normal metal electrodes. Moreover, we explored the interaction of the microscopic quantum coherence of the nanowires with the macroscopic quantum coherence of the superconductors. In superconducting Nb contacted InAs nanowire junctions, we have investigated the effect of temperature, magnetic field and electric field on the supercurrent. Owing to relatively high critical temperature of superconducting Nb (T{sub c} ∝ 9 K), we have observed the supercurrent up to 4 K for highly doped nanowire-based junctions, while for low doped nanowire-based junctions a full control of the supercurrent was achieved. Due to low transversal dimension of the nanowires, we have found a monotonous decay of the critical current in magnetic field dependent measurements. The experimental results were analyzed within narrow junction model which has been developed recently. At high bias voltages, we have observed subharmonic energy gap structures as a consequence of multiple Andreev reflection. Some of the nanowires were etched, such that the superconducting Nb electrodes are connected to both ends of the nanowire rather than covering the surface of the nanowire. As a result of well defined nanowire-superconductor interfaces, we have examined quasiparticle interference effect in magnetotransport measurements. Furthermore, we have developed a new junction geometry, such that one of the superconducting Nb electrodes is replaced by a superconducting Al. Owing to the smaller critical magnetic field of superconducting Al (B{sub c} ∝ 15-50,mT), compared to superconducting Nb (B{sub c} ∝ 3 T), we were able to studied
Modeling bidirectional transport of quantum dot nanoparticles in membrane nanotubes.
Kuznetsov, A V
2011-08-01
This paper develops a model of transport of quantum dot (QD) nanoparticles in membrane nanotubes (MNTs). It is assumed that QDs are transported inside intracellular organelles (called here nanoparticle-loaded vesicles, NLVs) that are propelled by either kinesin or dynein molecular motors while moving on microtubules (MTs). A vesicle may have both types of motors attached to it, but the motors are assumed to work in a cooperative fashion, meaning that at a given time the vesicle is moved by either kinesin or dynein motors. The motors are assumed not to work against each other, when one type of motors is pulling the vesicle, the other type is inactive. From time to time the motors may switch their roles: passive motors can become active motors and vice versa, resulting in the change of the vesicle's direction of motion. It is further assumed that QDs can escape NLVs and become free QDs, which are then transported by diffusion. Free QDs can be internalized by NLVs. The effects of two possible types of MT orientation in MNTs are investigated: when all MTs have a uniform polarity orientation, with their plus-ends directed toward one of the cells connected by an MNT, and when MTs have a mixed polarity orientation, with half of MTs having their plus-ends directed toward one of the cells and the other half having their plus-ends directed toward the other cell. Computational results are presented for three cases. The first case is when organelles are as likely to be transported by kinesin motors as by dynein motors. The second case is when organelles are more likely to be transported by kinesin motors than by dynein motors, and the third case is when NLVs do not associate with dynein motors at all. Copyright © 2011 Elsevier Inc. All rights reserved.
Transport of ultracold atoms through a quantum point contact
HäUsler, Samuel; Lebrat, Martin; Husmann, Dominik; Corman, Laura; Krinner, Sebastian; Grenier, Charles; Brantut, Jean-Philippe; Esslinger, Tilman
2017-04-01
We explore transport of neutral particles through a quantum point contact with tunable interactions. The contact is optically imprinted onto the center of a cigar-shaped cloud of fermionic lithium 6 atoms connected to macroscopic reservoirs on each side. We create a particle, spin or temperature bias between the reservoirs and measure the induced conductance. At weak attractive interactions we observe quantized particle conductance at multiples of 1/h, an upper bound for Fermi liquid reservoirs. Upon increasing attraction the plateaus contineously increase to non-universal values as high as 4/h before the gas becomes superfluid. At stronger interactions, the plateaus in the particle conductance disappear while spin transport is suppressed, signaling the emergence of superfluid pairing. The anomalous quantization challenges a Fermi liquid description of the normal phase, shedding new light on the strongly attractive gas. Complementary to particle and spin transport we study the thermoelectric response to a temperature gradient between the reservoirs. We observe that resonant interactions strongly modify the particle and energy evolution compared to the weakly attractive case.
Coherence-enhanced efficiency of feedback-driven quantum engines
Brandner, Kay; Bauer, Michael; Schmid, Michael T.; Seifert, Udo
2015-06-01
A genuine feature of projective quantum measurements is that they inevitably alter the mean energy of the observed system if the measured quantity does not commute with the Hamiltonian. Compared to the classical case, Jacobs proved that this additional energetic cost leads to a stronger bound on the work extractable after a single measurement from a system initially in thermal equilibrium (2009 Phys. Rev. A 80 012322). Here, we extend this bound to a large class of feedback-driven quantum engines operating periodically and in finite time. The bound thus implies a natural definition for the efficiency of information to work conversion in such devices. For a simple model consisting of a laser-driven two-level system, we maximize the efficiency with respect to the observable whose measurement is used to control the feedback operations. We find that the optimal observable typically does not commute with the Hamiltonian and hence would not be available in a classical two level system. This result reveals that periodic feedback engines operating in the quantum realm can exploit quantum coherences to enhance efficiency.
Theory of Transport Phenomena in Coherent Quantum Hall Bilayers
MacDonald, Allan H.; Chen, Hua; Sodemann, Inti
2015-03-01
We will describe a theory that allows to understand the anomalous transport properties of the excitonic condensate state occurring in quantum quantum Hall bilayers in terms of a picture in which the condensate phase is nearly uniform across the sample, and the strength of condensate coupling to interlayer tunneling processes is substantially reduced compared to the predictions of disorder-free microscopic mean-field theory. These ingredients provide a natural explanation for recently established I-V characteristics which feature a critical current above which the tunneling resistance abruptly increases and a non-local interaction between interlayer tunneling at the inner and outer edges of Corbino rings. We propose a microscopic picture in which disorder is the main agent responsible for the reduction of the effective interlayer tunneling strength. IS is supported by the Pappalardo Fellowship in Physics. HC and AHM are supported by DOE Division of Materials Sciences and Engineering Grant DE-FG03- 02ER45958 and Welch Foundation Grant TBF1473.
Narayanan, Karthikeyan; Yen, Swee Kuan; Dou, Qingqing; Padmanabhan, Parasuraman; Sudhaharan, Thankiah; Ahmed, Sohail; Ying, Jackie Y; Selvan, Subramanian Tamil
2013-01-01
Protein transport is an important phenomenon in biological systems. Proteins are transported via several mechanisms to reach their destined compartment of cell for its complete function. One such mechanism is the microtubule mediated protein transport. Up to now, there are no reports on synthetic systems mimicking the biological protein transport mechanism. Here we report a highly efficient method of mimicking the microtubule mediated protein transport using newly designed biotinylated peptides encompassing a microtubule-associated sequence (MTAS) and a nuclear localization signaling (NLS) sequence, and their final conjugation with streptavidin-coated CdSe/ZnS quantum dots (QDs). Our results demonstrate that these novel bio-conjugated QDs enhance the endosomal escape and promote targeted delivery into the nucleus of human mesenchymal stem cells via microtubules. Mimicking the cellular transport mechanism in stem cells is highly desirable for diagnostics, targeting and therapeutic applications, opening up new avenues in the area of drug delivery.
Local environment can enhance fidelity of quantum teleportation
BadziaĢ, Piotr; Horodecki, Michał; Horodecki, Paweł; Horodecki, Ryszard
2000-07-01
We show how an interaction with the environment can enhance fidelity of quantum teleportation. To this end, we present examples of states which cannot be made useful for teleportation by any local unitary transformations; nevertheless, after being subjected to a dissipative interaction with the local environment, the states allow for teleportation with genuinely quantum fidelity. The surprising fact here is that the necessary interaction does not require any intelligent action from the parties sharing the states. In passing, we produce some general results regarding optimization of teleportation fidelity by local action. We show that bistochastic processes cannot improve fidelity of two-qubit states. We also show that in order to have their fidelity improvable by a local process, the bipartite states must violate the so-called reduction criterion of separability.
Ripple enhanced transport of suprathermal alpha particles
International Nuclear Information System (INIS)
Tani, K.; Takizuka, T.; Azumi, M.
1986-01-01
The ripple enhanced transport of suprathermal alpha particles has been studied by the newly developed Monte-Carlo code in which the motion of banana orbit in a toroidal field ripple is described by a mapping method. The existence of ripple-resonance diffusion has been confirmed numerically. We have developed another new code in which the radial displacement of banana orbit is given by the diffusion coefficients from the mapping code or the orbit following Monte-Carlo code. The ripple loss of α particles during slowing down has been estimated by the mapping model code as well as the diffusion model code. From the comparison of the results with those from the orbit-following Monte-Carlo code, it has been found that all of them agree very well. (author)
International Nuclear Information System (INIS)
Zhang, Z. D.; Wang, J.
2014-01-01
We established a theoretical framework in terms of the curl flux, population landscape, and coherence for non-equilibrium quantum systems at steady state, through exploring the energy and charge transport in molecular processes. The curl quantum flux plays the key role in determining transport properties and the system reaches equilibrium when flux vanishes. The novel curl quantum flux reflects the degree of non-equilibriumness and the time-irreversibility. We found an analytical expression for the quantum flux and its relationship to the environmental pumping (non-equilibriumness quantified by the voltage away from the equilibrium) and the quantum tunneling. Furthermore, we investigated another quantum signature, the coherence, quantitatively measured by the non-zero off diagonal element of the density matrix. Populations of states give the probabilities of individual states and therefore quantify the population landscape. Both curl flux and coherence depend on steady state population landscape. Besides the environment-assistance which can give dramatic enhancement of coherence and quantum flux with high voltage at a fixed tunneling strength, the quantum flux is promoted by the coherence in the regime of small tunneling while reduced by the coherence in the regime of large tunneling, due to the non-monotonic relationship between the coherence and tunneling. This is in contrast to the previously found linear relationship. For the systems coupled to bosonic (photonic and phononic) reservoirs the flux is significantly promoted at large voltage while for fermionic (electronic) reservoirs the flux reaches a saturation after a significant enhancement at large voltage due to the Pauli exclusion principle. In view of the system as a quantum heat engine, we studied the non-equilibrium thermodynamics and established the analytical connections of curl quantum flux to the transport quantities such as energy (charge) transfer efficiency, chemical reaction efficiency, energy
Transport through Andreev bound states in a graphene quantum dot
Dirks, Travis; Hughes, Taylor L.; Lal, Siddhartha; Uchoa, Bruno; Chen, Yung-Fu; Chialvo, Cesar; Goldbart, Paul M.; Mason, Nadya
2011-05-01
When a low-energy electron is incident on an interface between a metal and superconductor, it causes the injection of a Cooper pair into the superconductor and the generation of a hole that reflects back into the metal--a process known as Andreev reflection. In confined geometries, this process can give rise to discrete Andreev bound states (ABS), which can enable transport of supercurrents through non-superconducting materials and have recently been proposed as a means of realizing solid-state qubits. Here, we report transport measurements of sharp, gate-tunable ABS formed in a superconductor-quantum dot (QD)-normal system realized on an exfoliated graphene sheet. The QD is formed in graphene beneath a superconducting contact as a result of a work-function mismatch. Individual ABS form when the discrete QD levels are proximity-coupled to the superconducting contact. Owing to the low density of states of graphene and the sensitivity of the QD levels to an applied gate voltage, the ABS spectra are narrow and can be continuously tuned down to zero energy by the gate voltage.
Minority Carrier Transport in Lead Sulfide Quantum Dot Photovoltaics.
Rekemeyer, Paul H; Chuang, Chia-Hao M; Bawendi, Moungi G; Gradečak, Silvija
2017-10-11
Lead sulfide quantum dots (PbS QDs) are an attractive material system for the development of low-cost photovoltaics (PV) due to their ease of processing and stability in air, with certified power conversion efficiencies exceeding 11%. However, even the best PbS QD PV devices are limited by diffusive transport, as the optical absorption length exceeds the minority carrier diffusion length. Understanding minority carrier transport in these devices will therefore be critical for future efficiency improvement. We utilize cross-sectional electron beam-induced current (EBIC) microscopy and develop methodology to quantify minority carrier diffusion length in PbS QD PV devices. We show that holes are the minority carriers in tetrabutylammonium iodide (TBAI)-treated PbS QD films due to the formation of a p-n junction with an ethanedithiol (EDT)-treated QD layer, whereas a heterojunction with n-type ZnO forms a weaker n + -n junction. This indicates that modifying the standard device architecture to include a p-type window layer would further boost the performance of PbS QD PV devices. Furthermore, quantitative EBIC measurements yield a lower bound of 110 nm for the hole diffusion length in TBAI-treated PbS QD films, which informs design rules for planar and ordered bulk heterojunction PV devices. Finally, the low-energy EBIC approach developed in our work is generally applicable to other emerging thin-film PV absorber materials with nanoscale diffusion lengths.
International Nuclear Information System (INIS)
Afsaneh, E.; Yavari, H.
2014-01-01
The superconducting reservoir effect on the current carrying transport of a double quantum dot in Markovian regime is investigated. For this purpose, a quantum master equation at finite temperature is derived for the many-body density matrix of an open quantum system. The dynamics and the steady-state properties of the double quantum dot system for arbitrary bias are studied. We will show that how the populations and coherencies of the system states are affected by superconducting leads. The energy parameter of system contains essentially four contributions due to dots system-electrodes coupling, intra dot coupling, two quantum dots inter coupling and superconducting gap. The coupling effect of each energy contribution is applied to currents and coherencies results. In addition, the effect of energy gap is studied by considering the amplitude and lifetime of coherencies to get more current through the system. (author)
Quantum Transport Simulation of High-Power 4.6-μm Quantum Cascade Lasers
Directory of Open Access Journals (Sweden)
Olafur Jonasson
2016-06-01
Full Text Available We present a quantum transport simulation of a 4.6- μ m quantum cascade laser (QCL operating at high power near room temperature. The simulation is based on a rigorous density-matrix-based formalism, in which the evolution of the single-electron density matrix follows a Markovian master equation in the presence of applied electric field and relevant scattering mechanisms. We show that it is important to allow for both position-dependent effective mass and for effective lowering of very thin barriers in order to obtain the band structure and the current-field characteristics comparable to experiment. Our calculations agree well with experiments over a wide range of temperatures. We predict a room-temperature threshold field of 62 . 5 kV/cm and a characteristic temperature for threshold-current-density variation of T 0 = 199 K . We also calculate electronic in-plane distributions, which are far from thermal, and show that subband electron temperatures can be hundreds to thousands of degrees higher than the heat sink. Finally, we emphasize the role of coherent tunneling current by looking at the size of coherences, the off-diagonal elements of the density matrix. At the design lasing field, efficient injection manifests itself in a large injector/upper lasing level coherence, which underscores the insufficiency of semiclassical techniques to address injection in QCLs.
Directory of Open Access Journals (Sweden)
Pengqin Shi
2016-09-01
Full Text Available Based on the time-nonlocal particle number-resolved master equation, we investigate the sequential electron transport through the interacting double quantum dots. Our calculations show that there exists the effect of energy renormalization in the dispersion of the bath interaction spectrum and it is sensitive to the the bandwidth of the bath. This effect would strongly affect the stationary current and its zero-frequency shot noise for weak inter-dot coherent coupling strength, but for strong inter-dot coupling regime, it is negligible due to the strong intrinsic Rabi coherent dynamics. Moreover, the possible observable effects of the energy renormalization in the noise spectrum are also investigated through the Rabi coherence signal. Finally, the non-Markovian effect is manifested in the finite-frequency noise spectrum with the appearance of quasisteps, and the magnitude of these quasisteps are modified by the dispersion function.
Verma, Upendra Kumar; Kumar, Brijesh
2017-10-01
We have modeled a multilayer quantum dot organic solar cell that explores the current-voltage characteristic of the solar cell whose characteristics can be tuned by varying the fabrication parameters of the quantum dots (QDs). The modeled device consists of a hole transport layer (HTL) which doubles up as photon absorbing layer, several quantum dot layers, and an electron transport layer (ETL). The conduction of charge carriers in HTL and ETL has been modeled by the drift-diffusion transport mechanism. The conduction and recombination in the quantum dot layers are described by a system of coupled rate equations incorporating tunneling and bimolecular recombination. Analysis of QD-solar cells shows improved device performance compared to the similar bilayer and trilayer device structures without QDs. Keeping other design parameters constant, solar cell characteristics can be controlled by the quantum dot layers. Bimolecular recombination coefficient of quantum dots is a prime factor which controls the open circuit voltage (VOC) without any significant reduction in short circuit current (JSC).
Zimmermann, Kristen A.; Inglefield, David L.; Zhang, Jianfei; Dorn, Harry C.; Long, Timothy E.; Rylander, Christopher G.; Rylander, M. Nichole
2014-01-01
Single-walled carbon nanohorns (SWNHs) have great potential to enhance thermal and chemotherapeutic drug efficiencies for cancer therapies. Despite their diverse capabilities, minimal research has been conducted so far to study nanoparticle intracellular transport, which is an important step in designing efficient therapies. SWNHs, like many other carbon nanomaterials, do not have inherent fluorescence properties making intracellular transport information difficult to obtain. The goals of this project were to (1) develop a simple reaction scheme to decorate the exohedral surface of SWNHs with fluorescent quantum dots (QDs) and improve conjugate stability, and (2) evaluate SWNH-QD conjugate cellular uptake kinetics and localization in various cancer cell lines of differing origins and morphologies. In this study, SWNHs were conjugated to CdSe/ZnS core/shell QDs using a unique approach to carbodiimide chemistry. Transmission electron microscopy and electron dispersive spectroscopy verified the conjugation of SWNHs and QDs. Cellular uptake kinetics and efficiency were characterized in three malignant cell lines: U-87 MG (glioblastoma), MDA-MB-231 (breast cancer), and AY-27 (bladder transitional cell carcinoma) using flow cytometry. Cellular distribution was verified by confocal microscopy, and cytotoxicity was also evaluated using an alamarBlue assay. Results indicate that cellular uptake kinetics and efficiency are highly dependent on cell type, highlighting the significance of studying nanoparticle transport at the cellular level. Nanoparticle intracellular transport investigations may provide information to optimize treatment parameters (e.g., SWNH concentration, treatment time, etc.) depending on tumor etiology.
Giant electron-hole transport asymmetry in ultra-short quantum transistors
McRae, A. C.; Tayari, V.; Porter, J. M.; Champagne, A. R.
2017-05-01
Making use of bipolar transport in single-wall carbon nanotube quantum transistors would permit a single device to operate as both a quantum dot and a ballistic conductor or as two quantum dots with different charging energies. Here we report ultra-clean 10 to 100 nm scale suspended nanotube transistors with a large electron-hole transport asymmetry. The devices consist of naked nanotube channels contacted with sections of tube under annealed gold. The annealed gold acts as an n-doping top gate, allowing coherent quantum transport, and can create nanometre-sharp barriers. These tunnel barriers define a single quantum dot whose charging energies to add an electron or a hole are vastly different (e-h charging energy asymmetry). We parameterize the e-h transport asymmetry by the ratio of the hole and electron charging energies ηe-h. This asymmetry is maximized for short channels and small band gap tubes. In a small band gap device, we demonstrate the fabrication of a dual functionality quantum device acting as a quantum dot for holes and a much longer quantum bus for electrons. In a 14 nm-long channel, ηe-h reaches up to 2.6 for a device with a band gap of 270 meV. The charging energies in this device exceed 100 meV.
Quantum and classical ballistic transport in a chaotic 2D electron channel
International Nuclear Information System (INIS)
Luna A, G.A.; Rodriguez, M.A.; Krokhin, A.; Na, K.; Mendez, A.
1998-01-01
We review recent results concerning the quantum and classical dynamical properties of ballistic electrons in a ripple channel, their transport properties and its classical-quantum correspondence is analyzed in terms of q uantum Poincare plots , energy level statistics, and certain features of the energy-band spectra. (Author)
Klimov, Victor I.
2017-05-01
Understanding and controlling carrier transport and recombination dynamics in colloidal quantum dot films is key to their application in electronic and optoelectronic devices. Towards this end, we have conducted transient photocurrent measurements to monitor transport through quantum confined band edge states in lead selenide quantum dots films as a function of pump fluence, temperature, electrical bias, and surface treatment. Room temperature dynamics reveal two distinct timescales of intra-dot geminate processes followed by non-geminate inter-dot processes. The non-geminate kinetics is well described by the recombination of holes with photoinjected and pre-existing electrons residing in mid-gap states. We find the mobility of the quantum-confined states shows no temperature dependence down to 6 K, indicating a tunneling mechanism of early time photoconductance. We present evidence of the importance of the exciton fine structure in controlling the low temperature photoconductance, whereby the nanoscale enhanced exchange interaction between electrons and holes in quantum dots introduces a barrier to charge separation. Finally, side-by-side comparison of photocurrent transients using excitation with low- and high-photon energies (1.5 vs. 3.0 eV) reveals clear signatures of carrier multiplication (CM), that is, generation of multiple excitons by single photons. Based on photocurrent measurements of quantum dot solids and optical measurements of solution based samples, we conclude that the CM efficiency is unaffected by strong inter-dot coupling. Therefore, the results of previous numerous spectroscopic CM studies conducted on dilute quantum dot suspensions should, in principle, be reproducible in electronically coupled QD films used in devices.
High-Fidelity Preservation of Quantum Information During Trapped-Ion Transport
Kaufmann, Peter; Gloger, Timm F.; Kaufmann, Delia; Johanning, Michael; Wunderlich, Christof
2018-01-01
A promising scheme for building scalable quantum simulators and computers is the synthesis of a scalable system using interconnected subsystems. A prerequisite for this approach is the ability to faithfully transfer quantum information between subsystems. With trapped atomic ions, this can be realized by transporting ions with quantum information encoded into their internal states. Here, we measure with high precision the fidelity of quantum information encoded into hyperfine states of a Yb171 + ion during ion transport in a microstructured Paul trap. Ramsey spectroscopy of the ion's internal state is interleaved with up to 4000 transport operations over a distance of 280 μ m each taking 12.8 μ s . We obtain a state fidelity of 99.9994 (-7+6) % per ion transport.
Transport phenomena in quantum wells and wires in presence of disorder and interactions
Vettchinkina, Valeria
2012-01-01
Present-day electronics employ circuits of smaller and smaller dimensions, and today the length scales are so small that the laws of physics which rule micro-cosmos, quantum mechanics, become directly important. This thesis reports on theoretical work on electron transport in different nanostructures. We have studied semiconductor quantum wells, layered materials where each layer can be only a few atomic layers thick, and transport in thin atomic wires. The layered materials have been stud...
Conformal Fabrication of Colloidal Quantum Dot Solids for Optically Enhanced Photovoltaics
Labelle, André J.
2015-05-26
© 2015 American Chemical Society. Colloidal quantum dots (CQD) are an attractive thin-film material for photovoltaic applications due to low material costs, ease of fabrication, and size-tunable band gap. Unfortunately, today they suffer from a compromise between light absorption and photocarrier extraction, a fact that currently prevents the complete harvest of incoming above-band-gap solar photons. We have investigated the use of structured substrates and/or electrodes to increase the effective light path through the active material and found that these designs require highly conformal application of the light-absorbing films to achieve the greatest enhancement. This conformality requirement derives from the need for maximal absorption enhancement combined with shortest-distance charge transport. Here we report on a means of processing highly conformal layer-by-layer deposited CQD absorber films onto microstructured, light-recycling electrodes. Specifically, we engineer surface hydrophilicity to achieve conformal deposition of upper layers atop underlying ones. We show that only with the application of conformal coating can we achieve optimal quantum efficiency and enhanced power conversion efficiency in structured-electrode CQD cells.
Anisotropic behavior of quantum transport in graphene superlattices
DEFF Research Database (Denmark)
Pedersen, Jesper Goor; Cummings, Aron W.; Roche, Stephan
2014-01-01
We report on the possibility to generate highly anisotropic quantum conductivity in disordered graphene-based superlattices. Our quantum simulations, based on an efficient real-space implementation of the Kubo-Greenwood formula, show that in disordered graphene superlattices the strength of multi...... orders of magnitude, and suggesting the possibility of building graphene electronic circuits based on the unique properties of chiral massless Dirac fermions in graphene.......We report on the possibility to generate highly anisotropic quantum conductivity in disordered graphene-based superlattices. Our quantum simulations, based on an efficient real-space implementation of the Kubo-Greenwood formula, show that in disordered graphene superlattices the strength...
Morr, Dirk K.
2017-05-01
Using the nonequilibrium Keldysh formalism, we investigate the spatial relation between the electrochemical potential measured in scanning tunneling potentiometry, and local current patterns over the entire range from the quantum to the classical transport regime. These quantities show similar spatial patterns near the quantum limit but are related by Ohm's law only in the classical regime. We demonstrate that defects induce a Landauer residual resistivity dipole in the electrochemical potential with the concomitant spatial current pattern representing the field lines of the dipole.
Spin transport properties in a double quantum ring with Rashba spin-orbit interaction
Naeimi, Azadeh S.; Eslami, Leila; Esmaeilzadeh, Mahdi; Abolhassani, Mohammad Reza
2013-01-01
We study spin-resolved electron transport in a double quantum ring in the presence of Rashba spin-orbit interaction and a magnetic flux using quantum waveguide theory. We show that, at the proper values of the system parameters such as the Rashba coupling constant, the radius of the rings, and the angle between the leads, the double quantum ring can act as a perfect electron spin-inverter with very high efficiency. Also, the double quantum ring can work as a spin switch. The spin polarization of transmitted electrons can be controlled and changed from -1 to +1 by using a magnetic flux.
Transport studies in p-type double quantum well samples
International Nuclear Information System (INIS)
Hyndman, R.J.
2000-01-01
The motivation for the study of double quantum well samples is that the extra spatial degree of freedom can modify the ground state energies of the system, leading to new and interesting many body effects. Electron bi-layers have been widely studied but the work presented here is the first systematic study of transport properties of a p-type, double quantum well system. The samples, grown on the 311 plane, consisted of two 100A GaAs wells separated by a 30A AlAs barrier. The thin barrier in our structures, gives rise to very strong inter-layer Coulombic interactions but in contrast to electron double quantum well samples, tunnelling between the two wells is very weak. This is due to the large effective mass of holes compared with electrons. It is possible to accurately control the total density of a sample and the relative occupancy of each well using front and back gates. A systematic study of the magnetoresistance properties of the p-type bi-layers, was carried out at low temperatures and in high magnetic fields, for samples covering a range of densities. Considerable care was required to obtain reliable results as the samples were extremely susceptible to electrical shock and were prone to drift in density slowly over time. With balanced wells, the very low tunnelling in the p-type bi-layer leads to a complete absence of all odd integers in both resistance and thermopower except for the v=1 state, ( v 1/2 in each layer) where v is the total Landau level filling factor. Unlike other FQHE features the v=1 state strengthens with increased density as inter-layer interactions increase in strength over intra-layer interactions. The state is also destroyed at a critical temperature, which is much lower than the measured activation temperature. This is taken as evidence for a finite temperature phase transition predicted for the bi-layer v=1. From the experimental observations, we construct a phase diagram for the state, which agree closely with theoretical predictions
Energy Technology Data Exchange (ETDEWEB)
Croy, Alexander
2010-06-30
In this thesis the time-resolved electron transport in quantum dot systems was studied. For this two different formalisms were presented: The nonequilibrium Green functions and the generalized quantum master equations. For both formalisms a propagation method for the numerical calculation of time-resolved expectation values, like the occupation and the electron current, was developed. For the demonstration of the propagation method two different question formulations were considered. On the one hand the stochastically driven resonant-level model was studied. On the other hand the pulse-induced transport through a double quantum dot was considered.
Coupled electron-phonon transport from molecular dynamics with quantum baths
DEFF Research Database (Denmark)
Lu, Jing Tao; Wang, J. S.
2009-01-01
Based on generalized quantum Langevin equations for the tight-binding wavefunction amplitudes and lattice displacements, electron and phonon quantum transport are obtained exactly using molecular dynamics (MD) in the ballistic regime. The electron-phonon interactions can be handled with a quasi......-classical approximation. Both charge and energy transport and their interplay can be studied. We compare the MD results with those of a fully quantum mechanical nonequilibrium Green's function (NEGF) approach for the electron currents. We find a ballistic to diffusive transition of the electron conduction in one...
International Nuclear Information System (INIS)
Matrasulov, D.U.
2012-01-01
Full text: Quantum graphs were introduced in physics more than X decades ago to describe electron transport in organic molecules. In mid eighties of the last century Schrodinger equation on graphs became subject of extensive study and boundary conditions, Green functions and the properties were treated comprehensively [1-3]. In nineties quantum graphs have been attractive topic in quantum chaos theory. However, on the practical viewpoint they can quite attractive for modelling of particle transport and quantum dynamics in discrete structures such as nanoscale networks, lattice structures, molecular wires etc. In this talk the introduction in quantum graphs are presented and prospects for their future practical applications are discussed. (author), References: [1] Tsampikos Kottos and Uzy Smilansky, Ann.Phys., 76, 274, (1999). [2] Sven Gnutzmann and Uzy Smilansky, Adv.Phys. 55, 527, (2006). [3] S. GnutzmannJ.P. Keating b, F. Piotet, Ann.Phys., 325, 2595, (2010).
What is novel in quantum transport for mesoscopics?
Indian Academy of Sciences (India)
Indeed, orthodox quantum kinetics would seem to say little about mesoscopics that has not been revealed – nearly effortlessly – by more popular means. Such is far from the case, however. The fact that kinetic theory remains very much in charge is best appreciated through the physics of a quantum point contact.
Transport through interacting quantum dots with Majorana fermions or phonons
Energy Technology Data Exchange (ETDEWEB)
Huetzen, Roland
2013-07-04
Recent advances in the search for Majorana fermions within condensed matter systems inspired the first part of the thesis. These hypothetical particles which are their own antiparticles are predicted to arise in the form of quasi-particle excitations called Majorana bound states at the surface of engineered condensed matter systems. An experimental detection is challenging since their defining property also implies that they possess no charge, no energy and no spin. This significantly reduces the possibilities to interact with them and get a proof of their existence from a measurement. The most promising experimental results are based on transport measurements where current-voltage-characteristics play the role of a spectroscopy signal. In this thesis, we investigate a single electron transistor setup which hosts a spatially separated pair of Majorana fermions with respect to their influence on its transport characteristics. We focus on a master equation approach including sequential and cotunneling contributions. After deducing all relevant rates we solve the system numerically over a broad parameter regime. For some limits, we also elaborate analytical solutions. In comparison with collaboratively worked out other methods we provide a broad understanding of the setup and make a proposal how our results could be used as a detection scheme for Majorana fermions. The second part of the thesis investigates the spinless Anderson-Holstein model which is the minimal model for molecular transport. It models a molecule with electronic and vibronic degrees of freedom which is placed between metallic leads at different chemical potentials to investigate again its transport properties. Also here we intended to gain access to a broad parameter regime and successfully extended the numerical ''iterative summation of path-integrals'' scheme to this model. It is based on a real-time path-integral approach in combination with the nonequilibrium Keldysh
Influences of a Side-Coupled Triple Quantum Dot on Kondo Transport Through a Quantum Dot
International Nuclear Information System (INIS)
Jiang Zhaotan; Yang Yannan; Qin Zhijie
2010-01-01
Kondo transport properties through a Kondo-type quantum dot (QD) with a side-coupled triple-QD structure are systematically investigated by using the non-equilibrium Green's function method. We firstly derive the formulae of the current, the linear conductance, the transmission coefficient, and the local density of states. Then we carry out the analytical and numerical studies and some universal conductance properties are obtained. It is shown that the number of the conductance valleys is intrinsically determined by the side-coupled QDs and at most equal to the number of the QDs included in the side-coupled structure in the asymmetric limit. In the process of forming the conductance valleys, the side-coupled QD system plays the dominant role while the couplings between the Kondo-type QD and the side-coupled structure play the subsidiary and indispensable roles. To testify the validity of the universal conductance properties, another different kinds of side-coupled triple-QD structures are considered. It should be emphasized that these universal properties are applicable in understanding this kind of systems with arbitrary many-QD side structures.
Anisotropy Enhancement of Thermal Energy Transport in Supported Black Phosphorene.
Chen, Jige; Chen, Shunda; Gao, Yi
2016-07-07
Thermal anisotropy along the basal plane of materials possesses both theoretical importance and application value in thermal transport and thermoelectricity. Though common two-dimensional materials may exhibit in-plane thermal anisotropy when suspended, thermal anisotropy would often disappear when supported on a substrate. In this Letter, we find a strong anisotropy enhancement of thermal energy transport in supported black phosphorene. The chiral preference of energy transport in the zigzag rather than the armchair direction is greatly enhanced by coupling to the substrate, up to a factor of approximately 2-fold compared to the suspended one. The enhancement originates from its puckered lattice structure, where the nonplanar armchair energy transport relies on the out-of-plane corrugation and thus would be hindered by the flexural suppression due to the substrate, while the planar zigzag energy transport is not. As a result, thermal conductivity of supported black phosphorene shows a consistent anisotropy enhancement under different temperatures and substrate coupling strengths.
Quantum size effects and transport phenomena in PbSe quantum wells and PbSe/EuS superlattices
Energy Technology Data Exchange (ETDEWEB)
Rogacheva, E. I.; Nashchekina, O. N.; Ol' khovskaya, S. I.; Sipatov, A. Yu. [National technical university Kharkov polytechnic institute, 21 Frunze St., Kharkov, 61002 (Ukraine); Dresselhaus, M. S. [Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge MA 02139 (United States)
2013-12-04
It is established that the room-temperature dependences of transport properties on the total thickness of PbSe layers d in PbSe/EuS superlattices exhibit an oscillatory behavior. It is shown that the oscillation period Δd practically coincides with the period of the thickness oscillations observed earlier in single PbSe/EuS quantum well. The non-monotonic character of these dependences is attributed to quantum size effects. The theoretically estimated and experimentally determined Δd values are in good agreement.
Energy transfer from quantum dots to metal-organic frameworks for enhanced light harvesting.
Jin, Shengye; Son, Ho-Jin; Farha, Omar K; Wiederrecht, Gary P; Hupp, Joseph T
2013-01-23
Because of their efficient energy-transport properties, porphyrin-based metal-organic frameworks (MOFs) are attractive compounds for solar photochemistry applications. However, their absorption bands provide limited coverage in the visible spectral range for light-harvesting applications. We report here the functionalization of porphyrin-based MOFs with CdSe/ZnS core/shell quantum dots (QDs) for the enhancement of light harvesting via energy transfer from the QDs to the MOFs. The broad absorption band of the QDs in the visible region offers greater coverage of the solar spectrum by QD-MOF hybrid structures. We show through time-resolved emission studies that photoexcitation of the QDs is followed by energy transfer to the MOFs with efficiencies of more than 80%. This sensitization approach can result in a >50% increase in the number of photons harvested by a single monolayer MOF structure with a monolayer of QDs on the surface of the MOF.
Spin-polarized quantum transport properties through flexible phosphorene
Chen, Mingyan; Yu, Zhizhou; Xie, Yiqun; Wang, Yin
2016-10-01
We report a first-principles study on the tunnel magnetoresistance (TMR) and spin-injection efficiency (SIE) through phosphorene with nickel electrodes under the mechanical tension and bending on the phosphorene region. Both the TMR and SIE are largely improved under these mechanical deformations. For the uniaxial tension (ɛy) varying from 0% to 15% applied along the armchair transport (y-)direction of the phosphorene, the TMR ratio is enhanced with a maximum of 107% at ɛy = 10%, while the SIE increases monotonously from 8% up to 43% with the increasing of the strain. Under the out-of-plane bending, the TMR overall increases from 7% to 50% within the bending ratio of 0%-3.9%, and meanwhile the SIE is largely improved to around 70%, as compared to that (30%) of the flat phosphorene. Such behaviors of the TMR and SIE are mainly affected by the transmission of spin-up electrons in the parallel configuration, which is highly dependent on the applied mechanical tension and bending. Our results indicate that the phosphorene based tunnel junctions have promising applications in flexible electronics.
Electron Transport in Quantum Dots Defined in Low-Dimensional Semiconductor Structures
Larsson, Marcus
2011-01-01
This thesis focuses on electron transport in single and double quantum dots defined in low-dimensional, narrow-band-gap III-V semiconductor materials. Fabrication schemes are presented for defining single and double quantum dots in lateral InGaAs/InP heterostructures, either by a combination of etching and local gating or solely by local top gating. The quantum dots are here electrostatically confined in at least one dimension. This allows for insitu control of the tunnel coupling of the quan...
Spin-related transport phenomena in HgTe-based quantum well structures
Energy Technology Data Exchange (ETDEWEB)
Koenig, Markus
2007-12-15
Within the scope of this thesis, spin related transport phenomena have been investigated in HgTe/Hg{sub 0.3}Cd{sub 0.7}Te quantum well structures. In our experiments, the existence of the quantum spin Hall (QSH) state was successfully demonstrated for the first time and the presented results provide clear evidence for the charge transport properties of the QSH state. Our experiments provide the first direct observation of the Aharonov-Casher (AC) effect in semiconductor structures. In conclusion, HgTe quantum well structures have proven to be an excellent template for studying spin-related transport phenomena: The QSH relies on the peculiar band structure of the material and the existence of both the spin Hall effect and the AC effect is a consequence of the substantial spin-orbit interaction. (orig.)
Parity effect of bipolar quantum Hall edge transport around graphene antidots.
Matsuo, Sadashige; Nakaharai, Shu; Komatsu, Katsuyoshi; Tsukagoshi, Kazuhito; Moriyama, Takahiro; Ono, Teruo; Kobayashi, Kensuke
2015-06-30
Parity effect, which means that even-odd property of an integer physical parameter results in an essential difference, ubiquitously appears and enables us to grasp its physical essence as the microscopic mechanism is less significant in coarse graining. Here we report a new parity effect of quantum Hall edge transport in graphene antidot devices with pn junctions (PNJs). We found and experimentally verified that the bipolar quantum Hall edge transport is drastically affected by the parity of the number of PNJs. This parity effect is universal in bipolar quantum Hall edge transport of not only graphene but also massless Dirac electron systems. These results offer a promising way to design electron interferometers in graphene.
Carbon nanostructured surfaces for enhanced heat transport
Taha, T.J.
2015-01-01
The advancement of high performance thermal systems has stimulated interest in methods to improve heat transfer rates. Considerable efforts have been made to increase heat transfer rates by implementing passive convective heat transfer enhancement methods that require no direct consumption of
Field-effect enhanced triboelectric colloidal quantum dot flexible sensor
Meng, Lingju; Xu, Qiwei; Fan, Shicheng; Dick, Carson R.; Wang, Xihua
2017-10-01
Flexible electronics, which is of great importance as fundamental sensor and communication technologies for many internet-of-things applications, has established a huge market encroaching into the trillion-dollar market of solid state electronics. For the capability of being processed by printing or spraying, colloidal quantum dots (CQDs) play an increasingly important role in flexible electronics. Although the electrical properties of CQD thin-films are expected to be stable on flexible substrates, their electrical performance could be tuned for applications in flexible touch sensors. Here, we report CQD touch sensors employing polydimethylsiloxane (PDMS) triboelectric films. The electrical response of touching activity is enhanced by incorporating CQD field-effect transistors into the device architecture. Thanks to the use of the CQD thin film as a current amplifier, the field-effect CQD touch sensor shows a fast response to various touching materials, even being bent to a large curvature. It also shows a much higher output current density compared to a PDMS triboelectric touch sensor.
Enhancement of Radiative Efficiency with Staggered InGaN Quantum Well Light Emitting Diodes
Energy Technology Data Exchange (ETDEWEB)
Tansu, Nelson; Dierolf, Volkmar; Huang, Gensheng; Penn, Samson; Zhao, Hongping; Liu, Guangyu; Li, Xiaohang; Poplawsky, Jonathan
2011-07-14
The technology on the large overlap InGaN QWs developed in this program is currently implemented in commercial technology in enhancing the internal quantum efficiency in major LED industry in US and Asia. The scientific finding from this work supported by the DOE enabled the implementation of this step-like staggered quantum well in the commercial LEDs.
Observation of quantum interference in molecular charge transport
DEFF Research Database (Denmark)
Guedon, Constant M.; Valkenier, Hennie; Markussen, Troels
2012-01-01
, phenomena such as giant magnetoresistance(5), Kondo effects(6) and conductance switching(7-11) have been observed in single molecules, and theorists have predicted that it should also be possible to observe quantum interference in molecular conductors(12-18), but until now all the evidence...
Superuniversal transport near a (2 +1 ) -dimensional quantum critical point
Rose, F.; Dupuis, N.
2017-09-01
We compute the zero-temperature conductivity in the two-dimensional quantum O (N ) model using a nonperturbative functional renormalization-group approach. At the quantum critical point we find a universal conductivity σ*/σQ (with σQ=q2/h the quantum of conductance and q the charge) in reasonable quantitative agreement with quantum Monte Carlo simulations and conformal bootstrap results. In the ordered phase the conductivity tensor is defined, when N ≥3 , by two independent elements, σA(ω ) and σB(ω ) , respectively associated with SO (N ) rotations which do and do not change the direction of the order parameter. Whereas σA(ω →0 ) corresponds to the response of a superfluid (or perfect inductance), the numerical solution of the flow equations shows that limω→0σB(ω ) /σQ=σB*/σQ is a superuniversal (i.e., N -independent) constant. These numerical results, as well as the known exact value σB*/σQ=π /8 in the large-N limit, allow us to conjecture that σB*/σQ=π /8 holds for all values of N , a result that can be understood as a consequence of gauge invariance and asymptotic freedom of the Goldstone bosons in the low-energy limit.
Enhanced Mobility-Lifetime Products in PbS Colloidal Quantum Dot Photovoltaics
Jeong, Kwang S.
2012-01-24
Figure Persented: Colloidal quantum dot (CQD) photovoltaics offer a promising approach to harvest the near-IR region of the solar spectrum, where half of the sun\\'s power reaching the earth resides. High external quantum efficiencies have been obtained in the visible region in lead chalcogenide CQD photovoltaics. However, the corresponding efficiencies for band gap radiation in the near-infrared lag behind because the thickness of CQD photovoltaic layers from which charge carriers can be extracted is limited by short carrier diffusion lengths. Here, we investigate, using a combination of electrical and optical characterization techniques, ligand passivation strategies aimed at tuning the density and energetic distribution of charge trap states at PbS nanocrystal surfaces. Electrical and optical measurements reveal a more than 7-fold enhancement of the mobility-lifetime product of PbS CQD films treated with 3-mercaptopropionic acid (MPA) in comparison to traditional organic passivation strategies that have been examined in the literature. We show by direct head-to-head comparison that the greater mobility-lifetime products of MPA-treated devices enable markedly greater short-circuit current and higher power conversion efficiency under AM1.5 illumination. Our findings highlight the importance of selecting ligand treatment strategies capable of passivating a diversity of surface states to enable shallower and lower density trap distributions for better transport and more efficient CQD solar cells. © 2011 American Chemical Society.
Enhanced Materials Based on Submonolayer Type-II Quantum Dots
Energy Technology Data Exchange (ETDEWEB)
Tamargo, Maria C [City College of New York, NY (United States); Kuskovsky, Igor L. [City Univ. (CUNY), NY (United States) Queens College; Meriles, Carlos [City College of New York, NY (United States); Noyan, Ismail C. [Columbia Univ., New York, NY (United States)
2017-04-15
We have investigated a nanostructured material known as sub-monolayer type-II QDs, made from wide bandgap II-VI semiconductors. Our goal is to understand and exploit their tunable optical and electrical properties by taking advantage of the type-II band alignment and quantum confinement effects. Type-II ZnTe quantum dots (QDs) in a ZnSe host are particularly interesting because of their relatively large valence band and conduction band offsets. In the current award we have developed new materials based on sub-monolayer type-II QDs that may be advantageous for photovoltaic and spintronics applications. We have also expanded the structural characterization of these materials by refining the X-ray diffraction methodologies needed to investigate them. In particular, we have 1) demonstrated ZnCdTe/ZnCdSe type-II QDs materials that have ideal properties for the development of novel high efficiency “intermediate band solar cells”, 2) we developed a comprehensive approach to describe and model the growth of these ultra-small type-II QDs, 3) analysis of the evolution of the photoluminescence (PL) emission, combined with other characterization probes allowed us to predict the size and density of the QDs as a function of the growth conditions, 4) we developed and implemented novel sophisticated X-ray diffraction techniques from which accurate size and shape of the buried type-II QDs could be extracted, 5) a correlation of the shape anisotropy with polarization dependent PL was observed, confirming the QDs detailed shape and providing insight about the effects of this shape anisotropy on the physical properties of the type-II QD systems, and 6) a detailed “time-resolved Kerr rotation” investigation has led to the demonstration of enhanced electron spin lifetimes for the samples with large densities of type-II QDs and an understanding of the interplay between the QDs and Te-isoelectroic centers, a defect that forms in the spacer layers that separate the QDs.
High Purity GaAs Far IR Photoconductor With Enhanced Quantum Efficieny, Phase I
National Aeronautics and Space Administration — This proposal introduces an innovative concept aimed to significantly enhance the quantum efficiency of a far-infrared GaAs photoconductor and achieve sensitivity...
Enhanced fault-tolerant quantum computing in d-level systems.
Campbell, Earl T
2014-12-05
Error-correcting codes protect quantum information and form the basis of fault-tolerant quantum computing. Leading proposals for fault-tolerant quantum computation require codes with an exceedingly rare property, a transversal non-Clifford gate. Codes with the desired property are presented for d-level qudit systems with prime d. The codes use n=d-1 qudits and can detect up to ∼d/3 errors. We quantify the performance of these codes for one approach to quantum computation known as magic-state distillation. Unlike prior work, we find performance is always enhanced by increasing d.
Quantum Engineering of States in Heterostructure-based Detectors for Enhance Performance
2017-05-26
each year. This is UIC’s highest teaching award. Elected to the College of Fellows, American Institute of Medical and Biomedical Engineers ...AFRL-AFOSR-VA-TR-2017-0109 Quantum engineering of heterostructure detectors for enhanced performance Michael Stroscio UNIVERSITY OF ILLINOIS Final...SUBTITLE Quantum Engineering of States in Heterostructure-based Detectors for Enhance Performance 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA9550-15-1
Julita, Julita
2017-01-01
This study is aimed to examine the quality of quantum learning imfluence toward the enhancement of mathematical problem solving ability of Senior High School students, both viewed entirely and based on mathematical initial ability (MIA) category. In particular, this study is aimed to examine enhancement difference of students’ mathematical problem solving ability in a whole and in each level of mathematical initial ability (high, medium and low) between students who receive quantum learning ...
Graphene quantum dots as enhanced plant growth regulators: effects on coriander and garlic plants.
Chakravarty, Disha; Erande, Manisha B; Late, Dattatray J
2015-10-01
We report investigations on the use of graphene quantum dots for growth enhancement in coriander (Coriandrum sativam L.) and garlic (Allium sativum) plants. The as-received seeds of coriander and garlic were treated with 0.2 mg mL(-1) of graphene quantum dots for 3 h before planting. Graphene quantum dots enhanced the growth rate in coriander and garlic plants, including leaves, roots, shoots, flowers and fruits, when the seeds were treated with graphene quantum dots. Our investigations open up the opportunity to use graphene quantum dots as plant growth regulators that can be used in a variety of other food plants for high yield. © 2015 Society of Chemical Industry.
International Nuclear Information System (INIS)
Casabone, B.
2015-01-01
Distributed quantum computing, an approach to scale up the computational power of quantum computers, requires entanglement between nodes of a quantum network. In our research group, two building blocks of schemes to entangle two ion-based quantum computers using cavity-based quantum interfaces have recently been demonstrated: ion-photon entanglement and ion-photon state mapping. In this thesis work, we extend the first building block in order to entangle two ions located in the same optical cavity. The entanglement generated by this protocol is efficient and heralded, and as it does not rely on the fact that ions interact with the same cavity, our results are a stepping stone towards the efficient generation of entanglement of remote ion-based quantum computers. In the second part of this thesis, we discuss how collective effects can be used to improve the performance of a cavity-based quantum interface. We show that by using two ions in the so-called superradiant state, the coupling strength between the two ions and the optical cavity is effectively increased compared to the single-ion case. As a complementary result, the creation of a state of two ions that exhibits a reduced coupling strength to the optical cavity, i.e., a subradiant state, is shown. Finally, we demonstrate a direct application of the increased coupling strength that the superradiant state exhibits by showing an enhanced version of the ion-photon state mapping process. By using the current setup and a second one that is being assembled, we intend to build a quantum network. The heralded ion-ion entanglement protocol presented in this thesis work will be used to entangle ions located in both setups, an experiment that requires photons generated in both apparatuses to be indistinguishable. Collective effects then can be used to modify the waveform of photons exiting the cavity in order to effect the desired photon indistinguishability. (author) [de
Quantum illumination for enhanced detection of Rayleigh-fading targets
Zhuang, Quntao; Zhang, Zheshen; Shapiro, Jeffrey H.
2017-08-01
Quantum illumination (QI) is an entanglement-enhanced sensing system whose performance advantage over a comparable classical system survives its usage in an entanglement-breaking scenario plagued by loss and noise. In particular, QI's error-probability exponent for discriminating between equally likely hypotheses of target absence or presence is 6 dB higher than that of the optimum classical system using the same transmitted power. This performance advantage, however, presumes that the target return, when present, has known amplitude and phase, a situation that seldom occurs in light detection and ranging (lidar) applications. At lidar wavelengths, most target surfaces are sufficiently rough that their returns are speckled, i.e., they have Rayleigh-distributed amplitudes and uniformly distributed phases. QI's optical parametric amplifier receiver—which affords a 3 dB better-than-classical error-probability exponent for a return with known amplitude and phase—fails to offer any performance gain for Rayleigh-fading targets. We show that the sum-frequency generation receiver [Zhuang et al., Phys. Rev. Lett. 118, 040801 (2017), 10.1103/PhysRevLett.118.040801]—whose error-probability exponent for a nonfading target achieves QI's full 6 dB advantage over optimum classical operation—outperforms the classical system for Rayleigh-fading targets. In this case, QI's advantage is subexponential: its error probability is lower than the classical system's by a factor of 1 /ln(M κ ¯NS/NB) , when M κ ¯NS/NB≫1 , with M ≫1 being the QI transmitter's time-bandwidth product, NS≪1 its brightness, κ ¯ the target return's average intensity, and NB the background light's brightness.
Enhanced arbitrated quantum signature scheme using Bell states
International Nuclear Information System (INIS)
Wang Chao; Liu Jian-Wei; Shang Tao
2014-01-01
We investigate the existing arbitrated quantum signature schemes as well as their cryptanalysis, including intercept-resend attack and denial-of-service attack. By exploring the loopholes of these schemes, a malicious signatory may successfully disavow signed messages, or the receiver may actively negate the signature from the signatory without being detected. By modifying the existing schemes, we develop counter-measures to these attacks using Bell states. The newly proposed scheme puts forward the security of arbitrated quantum signature. Furthermore, several valuable topics are also presented for further research of the quantum signature scheme
Chiral heat transport in driven quantum Hall and spin Hall edge states
Arrachea, Liliana; Fradkin, Eduardo
2012-02-01
We consider a model for an edge state of electronic systems in the quantum Hall regime with filling ν=1 as well as in the quantum spin Hall regime. In both cases the system is in contact with two reservoirs by tunneling at point contacts. Both systems are locally driven by applying an ac voltage in one of the contacts. By weakly coupling them to a third reservoir, the transport of the generated heat is studied in two different ways: i) when the third reservoir acts as a thermometer the local temperature is sensed, and ii) when the third reservoir acts as a voltage probe the time-dependent local voltage is sensed. Our results indicate a chiral propagation of the heat along the edge in the quantum Hall case and in the quantum spin Hall case (if the injected electrons are spin polarized). The temperature profile shows that electrons along the edge thermalize with the closest upstream reservoir.
Plasmon enhanced silver quantum cluster fluorescence for biochemical applications
DEFF Research Database (Denmark)
Bernard, S.; Kutter, Jörg P.; Mogensen, K. B.
2014-01-01
Fluorescence microscopy of individual silver quantum clusters on the surface of silver nanoparticles reveals strong photoactivated emission under blue light excitation [1-4]. In this work, silver nanoparticles are produced by annealing silver thin films deposited on a glass substrate and silver...... quantum clusters are subsequently synthesized at the surface of the nanoparticles by photoactivation in presence of Ag+ cations in solution. The photogeneration of these silver quantum clusters leads to a great increase in the fluorescent signal. This photoactivated surface can then be used for sensing...... purposes. It was found, that in presence of a strong nucleophile (such as CN-), silver quantum clusters are dissolved into non-fluorescing AgCN complexes, resulting in a fast and observable decrease of the fluorescent signal....
Inelastic Quantum Transport in Superlattices: Success and Failure of the Boltzmann Equation
DEFF Research Database (Denmark)
Wacker, Andreas; Jauho, Antti-Pekka; Rott, Stephan
1999-01-01
the whole held range from linear response to negative differential conductivity. The quantum results are compared with the respective results obtained from a Monte Carlo solution of the Boltzmann equation. Our analysis thus sets the limits of validity for the semiclassical theory in a nonlinear transport...
Electron transport in n-doped Si/SiGe quantum cascade structures
Lazic, I.; Ikonic, Z.; Milanovic, V.; Kelsall, R.W.; Indjin, D.; Harrison, P.
2007-01-01
An electron transport model in n-Si/SiGe quantum cascade or superlattice structures is described. The model uses the electronic structure calculated within the effective-mass complex-energy framework, separately for perpendicular (Xz) and in-plane (Xxy) valleys, the degeneracy of which is lifted by
Ab initio calculation of transport properties between PbSe quantum dots facets with iodide ligands
Wang, B.; Patterson, R.; Chen, W.; Zhang, Z.; Yang, J.; Huang, S.; Shrestha, S.; Conibeer, G.
2018-01-01
The transport properties between Lead Selenide (PbSe) quantum dots decorated with iodide ligands has been studied using density functional theory (DFT). Quantum conductance at each selected energy levels has been calculated along with total density of states and projected density of states. The DFT calculation is carried on using a grid-based planar augmented wave (GPAW) code incorporated with the linear combination of atomic orbital (LCAO) mode and Perdew Burke Ernzerhof (PBE) exchange-correlation functional. Three iodide ligand attached low index facets including (001), (011), (111) are investigated in this work. P-orbital of iodide ligand majorly contributes to density of state (DOS) at near top valence band resulting a significant quantum conductance, whereas DOS of Pb p-orbital shows minor influence. Various values of quantum conductance observed along different planes are possibly reasoned from a combined effect electrical field over topmost surface and total distance between adjacent facets. Ligands attached to (001) and (011) planes possess similar bond length whereas it is significantly shortened in (111) plane, whereas transport between (011) has an overall low value due to newly formed electric field. On the other hand, (111) plane with a net surface dipole perpendicular to surface layers leading to stronger electron coupling suggests an apparent increase of transport probability. Apart from previously mentioned, the maximum transport energy levels located several eVs (1 2 eVs) from the edge of valence band top.
Wees, B.J. van; Kouwenhoven, L.P.; Enden, A. van der; Harmans, C.J.P.M.
1991-01-01
We describe transport experiments performed on ballistic submicron devices which are defined in the two dimensional electron gas of GaAs/AlGaAs heterostructures by means of metallic gates. Conductance measurements on single quantum dots reveal the formation of magnetically induced zero-dimensional
Two-terminal transport along a proximity-induced superconducting quantum Hall edge
Gamayun, O.; Hutasoit, J.A.; Cheianov, V.V.
2017-01-01
We study electric transport along an integer quantum Hall edge where the proximity effect is induced due to a coupling to a superconductor. Such an edge exhibits two Majorana-Weyl fermions with different group velocities set by the induced superconducting pairing. We show that this structure of the
Directory of Open Access Journals (Sweden)
Jiahui Li
2016-10-01
Full Text Available All-inorganic quantum dot light emitting diodes (QLEDs have gained great attention as a result of their high stability under oxygen-rich, humid and high current working conditions. In this work, we have fabricated an all-inorganic QLED device (FTO/NiO/QDs/AZO/Ag with sandwich-structure, wherein the inorganic metal oxides thin films of NiO and AZO were employed as hole and electron transport layers, respectively. The porous NiO layer with vertical lamellar nanosheets interconnected microstructure have been directly synthesized on the substrate of conductive FTO glass and increased the wettability of CdSe@ZnS QDs, which result in an enhancement of current transport performance of the QLED.
Majorana fermion modulated nonequilibrium transport through double quantum dots
International Nuclear Information System (INIS)
Deng, Ming-Xun; Wang, Rui-Qiang; Ai, Bao-Quan; Yang, Mou; Hu, Liang-Bin; Zhong, Qing-Hu; Wang, Guang-Hui
2014-01-01
Nonequilibrium electronic transports through a double-QD-Majorana coupling system are studied with a purpose to extract the information to identify Majorana bound states (MBSs). It is found that MBSs can help form various transport processes, including the nonlocal crossed Andreev reflection, local resonant Andreev reflection, and cotunneling, depending on the relative position of two dot levels. These processes enrich the signature of average currents and noise correlations to probe the nature of MBSs. We further demonstrate the switching between the current peaks of crossed Andreev reflection and cotunneling, which is closely related to the nonlocal nature of Majorana fermions. We also propose effective physical pictures to understand these Majorana-assisted transports. - Highlights: • Majorana fermions are characterized in the signature of currents and noises. • Three types of tunneling mechanisms are realized separately. • The switching of crossed Andreev reflection and cotunneling is realized. • Concrete physical pictures are proposed to understand Majorana-assisted transports
Green-function approach to transport phenomena in quantum pumps
Arrachea, Liliana
2005-09-01
We present a general treatment based on nonequilibrium Green functions to study transport phenomena in systems described by tight-binding Hamiltonians coupled to reservoirs and with one or more time-periodic potentials. We apply this treatment to the study of transport phenomena in a double barrier structure with one and two ac potentials. Among other properties, we discuss the origin of the sign of the net current.
Enhanced photocurrent density of HTM-free perovskite solar cells by carbon quantum dots
Zou, Haiyuan; Guo, Daipeng; He, Bowen; Yu, Jiaguo; Fan, Ke
2018-02-01
Full-printable and hole transport material (HTM)-free perovskite solar cells (PSCs) with carbon counter electrodes feature high stability and low cost. However, the perovskite film prepared by conventional one-step solution-coating method always shows a relatively poor coverage on the substrate, leading to the limit of the photocurrent density. In this study, we incorporated carbon quantum dots (CQDs) in the perovskite films, and investigated their effects on the performance of TiO2 nanosheet-based and HTM-free PSCs. It was found that the addition of CQDs to the perovskite film can enhance the photocurrent density of PSCs, and the optimal PSC with 0.1% CQDs evolved 60% higher photocurrent density than the pristine one. The improved photocurrent density was attributed to the heterogeneous nuclei derived from CQDs during perovskite crystallization, which would increase amount of perovskite nuclei and form a fine perovskite grain, leading to a better coverage on the substrate. Moreover, due to the excellent conductivity, CQDs in perovskite films could efficiently transport the photo-excited electrons, accelerating the separation and mobilization of charge carriers. This study presents the incorporation of CQDs in perovskite as an efficient approach to promote the performance of HTM-free PSCs.
Sadhukhan, Debasis; Roy, Sudipto Singha; Rakshit, Debraj; Prabhu, R; Sen De, Aditi; Sen, Ujjwal
2016-01-01
Classical correlation functions of ground states typically decay exponentially and polynomially, respectively, for gapped and gapless short-range quantum spin systems. In such systems, entanglement decays exponentially even at the quantum critical points. However, quantum discord, an information-theoretic quantum correlation measure, survives long lattice distances. We investigate the effects of quenched disorder on quantum correlation lengths of quenched averaged entanglement and quantum discord, in the anisotropic XY and XYZ spin glass and random field chains. We find that there is virtually neither reduction nor enhancement in entanglement length while quantum discord length increases significantly with the introduction of the quenched disorder.
Spin-Filtering Transport in Double Parallel Quantum Wires on a Graphene Sheet
Yang, Fu-Bin; Cheng, Yan; Liu, Fu-Ti; Chen, Xiang-Rong; Cai, Ling-Cang
2015-03-01
We theoretically investigate the spin filtering transport of double parallel quantum wires (QWs) side-coupled to a graphene sheet and sandwiched between two ferromagnetic (FM) leads. The dependences of the wire-graphene coupling strength, wire-wire coupling strength, as well as the spin polarization of the ferromagnetic leads are studied. It is found that the wire-graphene coupling strength tends to reduce the current and the wire-wire coupling strength can first reinforce and then decrease the current. The spin polarization strength has an enhanced (identical) effect on the current under the parallel (anti-parallel) alignment of the FM leads, which gives rise to an obvious spin-filter and tunnel magnetoresistance (TMR) effect. Our results suggest that such a theoretical model can stimulate some experimental investigations about the spin-filter devices. Supported by the National Natural Science Foundation of China under Grant Nos. 11174214, 11204192, the NSAF Joint Fund Jointly set up by the National Natural Science Foundation of China and the Chinese Academy of Engineering Physics under Grant Nos. U1230201 and U1430117
Graphene Quantum Dots Embedded in Bi2Te3Nanosheets To Enhance Thermoelectric Performance.
Li, Shuankui; Fan, Tianju; Liu, Xuerui; Liu, Fusheng; Meng, Hong; Liu, Yidong; Pan, Feng
2017-02-01
Novel Bi 2 Te 3 /graphene quantum dots (Bi 2 Te 3 /GQDs) hybrid nanosheets with a unique structure that GQDs are homogeneously embedded in the Bi 2 Te 3 nanosheet matrix have been synthesized by a simple solution-based synthesis strategy. A significantly reduced thermal conductivity and enhanced powder factor are observed in the Bi 2 Te 3 /GQDs hybrid nanosheets, which is ascribed to the optimized thermoelectric transport properties of the Bi 2 Te 3 /GQDs interface. Furthermore, by varying the size of the GQDs, the thermoelectric performance of Bi 2 Te 3 /GQDs hybrid nanostructures could be further enhanced, which could be attributed to the optimization of the density and dispersion manner of the GQDs in the Bi 2 Te 3 matrix. A maximum ZT of 0.55 is obtained at 425 K for the Bi 2 Te 3 /GQDs-20 nm, which is higher than that of Bi 2 Te 3 without hybrid nanostrucure. This work provides insights for the structural design and synthesis of Bi 2 Te 3 -based hybrid thermoelectric materials, which will be important for future development of broadly functional material systems.
Chen, Chun-Nan; Luo, Win-Jet; Shyu, Feng-Lin; Chung, Hsien-Ching; Lin, Chiun-Yan; Wu, Jhao-Ying
2018-01-01
Using a non-equilibrium Green’s function framework in combination with the complex energy-band method, an atomistic full-quantum model for solving quantum transport problems for a zigzag-edge graphene nanoribbon (zGNR) structure is proposed. For transport calculations, the mathematical expressions from the theory for zGNR-based device structures are derived in detail. The transport properties of zGNR-based devices are calculated and studied in detail using the proposed method.
Temperature dependent transport of two dimensional electrons in the integral quantum Hall regime
International Nuclear Information System (INIS)
Wi, H.P.
1986-01-01
This thesis is concerned with the temperature dependent electronic transport properties of a two dimensional electron gas subject to background potential fluctuations and a perpendicular magnetic field. The author carried out an extensive temperature dependent study of the transport coefficients, in the region of an integral quantum plateau, in an In/sub x/Ga/sub 1-x/As/InP heterostructure for 4.2K 10 cm -2 meV -1 ) even at the middle between two Landau levels, which is unexpected from model calculations based on short ranged randomness. In addition, the different T dependent behavior of rho/sub xx/ between the states in the tails and those near the center of a Landau level, indicates the existence of different electron states in a Landau level. Additionally, the author reports T-dependent transport measurements in the transition region between two quantum plateaus in several different materials
Quantum Transmission Conditions for Diffusive Transport in Graphene with Steep Potentials
Barletti, Luigi; Negulescu, Claudia
2018-05-01
We present a formal derivation of a drift-diffusion model for stationary electron transport in graphene, in presence of sharp potential profiles, such as barriers and steps. Assuming the electric potential to have steep variations within a strip of vanishing width on a macroscopic scale, such strip is viewed as a quantum interface that couples the classical regions at its left and right sides. In the two classical regions, where the potential is assumed to be smooth, electron and hole transport is described in terms of semiclassical kinetic equations. The diffusive limit of the kinetic model is derived by means of a Hilbert expansion and a boundary layer analysis, and consists of drift-diffusion equations in the classical regions, coupled by quantum diffusive transmission conditions through the interface. The boundary layer analysis leads to the discussion of a four-fold Milne (half-space, half-range) transport problem.
Issues in tokamak/stellarator transport and confinement enhancement mechanisms
Energy Technology Data Exchange (ETDEWEB)
Perkins, F.W.
1990-08-01
At present, the mechanism for anomalous energy transport in low-{beta} toroidal plasmas -- tokamaks and stellarators -- remains unclear, although transport by turbulent E {times} B velocities associated with nonlinear, fine-scale microinstabilities is a leading candidate. This article discusses basic theoretical concepts of various transport and confinement enhancement mechanisms as well as experimental ramifications which would enable one to distinguish among them and hence identify a dominant transport mechanism. While many of the predictions of fine-scale turbulence are born out by experiment, notable contradictions exist. Projections of ignition margin rest both on the scaling properties of the confinement mechanism and on the criteria for entering enhanced confinement regimes. At present, the greatest uncertainties lie with the basis for scaling confinement enhancement criteria. A series of questions, to be answered by new experimental/theoretical work, is posed to resolve these outstanding contradictions (or refute the fine-scale turbulence model) and to establish confinement enhancement criteria. 73 refs., 4 figs., 5 tabs.
Nonequilibrium Transport through a Spinful Quantum Dot with Superconducting Leads
DEFF Research Database (Denmark)
Andersen, Brian Møller; Flensberg, Karsten; Koerting, Verena
2011-01-01
We study the nonlinear cotunneling current through a spinful quantum dot contacted by two superconducting leads. Applying a general nonequilibrium Green function formalism to an effective Kondo model, we study the rich variation in the IV characteristics with varying asymmetry in the tunnel...... coupling to source and drain electrodes. The current is found to be carried, respectively, by multiple Andreev reflections in the symmetric limit, and by spin-induced Yu-Shiba-Rusinov bound states in the strongly asymmetric limit. The interplay between these two mechanisms leads to qualitatively different...... IV characteristics in the crossover regime of intermediate symmetry, consistent with recent experimental observations of negative differential conductance and repositioned conductance peaks in subgap cotunneling spectroscopy....
Quantum-enhanced deliberation of learning agents using trapped ions
Dunjko, V.; Friis, N.; Briegel, H. J.
2015-02-01
A scheme that successfully employs quantum mechanics in the design of autonomous learning agents has recently been reported in the context of the projective simulation (PS) model for artificial intelligence. In that approach, the key feature of a PS agent, a specific type of memory which is explored via random walks, was shown to be amenable to quantization, allowing for a speed-up. In this work we propose an implementation of such classical and quantum agents in systems of trapped ions. We employ a generic construction by which the classical agents are ‘upgraded’ to their quantum counterparts by a nested process of adding coherent control, and we outline how this construction can be realized in ion traps. Our results provide a flexible modular architecture for the design of PS agents. Furthermore, we present numerical simulations of simple PS agents which analyze the robustness of our proposal under certain noise models.
Electronic transport through a quantum dot chain with strong dot-lead coupling
International Nuclear Information System (INIS)
Liu, Yu; Zheng, Yisong; Gong, Weijiang; Gao, Wenzhu; Lue, Tianquan
2007-01-01
By means of the non-equilibrium Green function technique, the electronic transport through an N-quantum-dot chain is theoretically studied. By calculating the linear conductance spectrum and the local density of states in quantum dots, we find the resonant peaks in the spectra coincides with the eigen-energies of the N-quantum-dot chain when the dot-lead coupling is relatively weak. With the increase of the dot-lead coupling, such a correspondence becomes inaccurate. When the dot-lead coupling exceeds twice the interdot coupling, such a mapping collapses completely. The linear conductance turn to reflect the eigen-energies of the (N-2)- or (N-1)-quantum dot chain instead. The two peripheral quantum dots do not manifest themselves in the linear conductance spectrum. More interestingly, with the further increase of the dot-lead coupling, the system behaves just like an (N-2)- or (N-1)-quantum dot chain in weak dot-lead coupling limit, since the resonant peaks becomes narrower with the increase of dot-lead coupling
Quantum mechanics of excitation transport in photosynthetic complexes: a key issues review.
Levi, Federico; Mostarda, Stefano; Rao, Francesco; Mintert, Florian
2015-07-01
For a long time microscopic physical descriptions of biological processes have been based on quantum mechanical concepts and tools, and routinely employed by chemical physicists and quantum chemists. However, the last ten years have witnessed new developments on these studies from a different perspective, rooted in the framework of quantum information theory. The process that more, than others, has been subject of intense research is the transfer of excitation energy in photosynthetic light-harvesting complexes, a consequence of the unexpected experimental discovery of oscillating signals in such highly noisy systems. The fundamental interdisciplinary nature of this research makes it extremely fascinating, but can also constitute an obstacle to its advance. Here in this review our objective is to provide an essential summary of the progress made in the theoretical description of excitation energy dynamics in photosynthetic systems from a quantum mechanical perspective, with the goal of unifying the language employed by the different communities. This is initially realized through a stepwise presentation of the fundamental building blocks used to model excitation transfer, including protein dynamics and the theory of open quantum system. Afterwards, we shall review how these models have evolved as a consequence of experimental discoveries; this will lead us to present the numerical techniques that have been introduced to quantitatively describe photo-absorbed energy dynamics. Finally, we shall discuss which mechanisms have been proposed to explain the unusual coherent nature of excitation transport and what insights have been gathered so far on the potential functional role of such quantum features.
Conserving GW scheme for nonequilibrium quantum transport in molecular contacts
DEFF Research Database (Denmark)
Thygesen, Kristian Sommer; Rubio, Angel
2008-01-01
We give a detailed presentation of our recent scheme to include correlation effects in molecular transport calculations using the nonequilibrium Keldysh formalism. The scheme is general and can be used with any quasiparticle self-energy, but for practical reasons, we mainly specialize to the so-c...
Increased fluorescence of PbS quantum dots in photonic crystals by excitation enhancement
Barth, Carlo; Roder, Sebastian; Brodoceanu, Daniel; Kraus, Tobias; Hammerschmidt, Martin; Burger, Sven; Becker, Christiane
2017-07-01
We report on the enhanced fluorescence of lead sulfide quantum dots interacting with leaky modes of slab-type silicon photonic crystals. The photonic crystal slabs were fabricated, supporting leaky modes in the near infrared wavelength range. Lead sulfite quantum dots which are resonant in the same spectral range were prepared in a thin layer above the slab. We selectively excited the leaky modes by tuning the wavelength and angle of incidence of the laser source and measured distinct resonances of enhanced fluorescence. By an appropriate experiment design, we ruled out directional light extraction effects and determined the impact of enhanced excitation. Three-dimensional numerical simulations consistently explain the experimental findings by strong near-field enhancements in the vicinity of the photonic crystal surface. Our study provides a basis for systematic tailoring of photonic crystals used in biological applications such as biosensing and single molecule detection, as well as quantum dot solar cells and spectral conversion applications.
Plasmonic emission enhancement of colloidal quantum dots in the presence of bimetallic nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Sadeghi, S. M., E-mail: seyed.sadeghi@uah.edu [Department of Physics, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States); Nano and Micro Device Center, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States); Hatef, A.; Meunier, M. [Ecole Polytechnique de Montreal, Laser Processing and Plasmonics Laboratory, Engineering Physics Department, Montreal, Quebec H3C 3A7 (Canada); Nejat, A. [Department of Electrical and Computer Engineering, Boston University, 8 Saint Marys Street, Boston, Massachusetts 02215 (United States); Campbell, Q. [Department of Physics, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States)
2014-04-07
We studied plasmonic features of bimetallic nanostructures consisting of gold nanoisland cores semi-coated with a chromium layer and explored how they influence emission of CdSe/ZnS quantum dots. We showed that, compared with chromium-covered glass substrates without the gold cores, the bimetallic nanostructures could significantly enhance the emission of the quantum dots. We studied the impact of the excitation intensity and thickness of the chromium layer on this process and utilized numerical means to identify the mechanisms behind it. Our results suggest that when the chromium layer is thin, the enhancement process is the result of the bimetallic plasmonic features of the nanostructures. As the chromium layer becomes thick, the impact of the gold cores is screened and the enhancement mostly happens mostly via the field enhancement of chromium nanoparticles in the absence of significant energy transfer from the quantum dots to these nanoparticles.
Density functional approximation for spin dependent quantum transport in magnetic nano structures
International Nuclear Information System (INIS)
Nyunt, Khine
2009-01-01
In quasi-classical theoretical framework, the transport of electrons and holes in semiconductor devices is treated with the Boltzmann transport equation or quantum-mechanical energy band theory - viz., the effective mass approximation and the random phase approximation. On the other hand, in the mesoscopic, nano electronic devices, for three- and lower- dimensional structures with nanometer scaling, the wave properties, spin, charge and the interactions between spin and charge of electrons are fully utilized, such as in artificial mini-Brillouin zones, quantum size effects, Coulomb blockade of single-electron tunneling and spin-polarized giant magnetoresistance tunneling. The complexity associated with the classical quantum-mechanical formalism in the study of transport in magnetic nano structures can be avoided by applying the so-called, Hohenberg-Kohns density functional theory. In particular, the N-electron problem is formulated as N one-electron equations where each electron interacts with all other electrons via an effective exchange-correlation potential. These interactions are augmented using the electron charge density. Plane wave sets and total energy pseudo-potential methods can be used self-consistently, to solve the Kohn-Sham one-electron equations. Because of the limitations of quasi-classical theory, it is more appropriate to treat the magneto-transport problem in nano structures by using quantum many-body theory. The starting point of the quantum transport theory is to take an external field as a perturbation for the many-particle system in equilibrium. This leads to a linear response and gives corresponding transport coefficients. One useful application of the Greens function techniques in quantum magneto-transport is to convert a homogeneous differential equation into an integral equation, viz., as in the time-dependent Schrodinger equation. We have applied to scattering of nano structural defects (impurities) in the electron gas (metal) as many
Finite speed heat transport in a quantum spin chain after quenched local cooling
Fries, Pascal; Hinrichsen, Haye
2017-04-01
We study the dynamics of an initially thermalized spin chain in the quantum XY-model, after sudden coupling to a heat bath of lower temperature at one end of the chain. In the semi-classical limit we see an exponential decay of the system-bath heatflux by exact solution of the reduced dynamics. In the full quantum description however, we numerically find the heatflux to reach intermediate plateaus where it is approximately constant—a phenomenon that we attribute to the finite speed of heat transport via spin waves.
Carrier transport in THz quantum cascade lasers: Are Green's functions necessary?
Energy Technology Data Exchange (ETDEWEB)
Matyas, A; Jirauschek, C [Emmy Noether Research Group ' Modeling of Quantum Cascade Devices' , TU Muenchen, D-80333 Muenchen (Germany); Kubis, T [Walter Schottky Institute, TU Muenchen, D-85748 Garching (Germany); Lugli, P, E-mail: alparmat@mytum.d [Institute of Nanoelectronics, TU Muenchen, D-80333 Muenchen (Germany)
2009-11-15
We have applied two different simulation models for the stationary carrier transport and optical gain analysis in resonant phonon depopulation THz Quantum Cascade Lasers (QCLs), based on the semiclassical ensemble Monte Carlo (EMC) and fully quantum mechanical non-equilibrium Green's functions (NEGF) method, respectively. We find in the incoherent regime near and above the threshold current a qualitative and quantitative agreement of both methods. Therefore, we show that THz-QCLs can be successfully optimized utilizing the numerically efficient EMC method.
Plasmon enhanced silver quantum cluster fluorescence for biochemical applications
DEFF Research Database (Denmark)
Bernard, S.; Kutter, Jörg P.; Mogensen, K. B.
2014-01-01
Fluorescence microscopy of individual silver quantum clusters on the surface of silver nanoparticles reveals strong photoactivated emission under blue light excitation [1-4]. In this work, silver nanoparticles are produced by annealing silver thin films deposited on a glass substrate and silver...
Field enhancement at metallic interfaces due to quantum confinement
DEFF Research Database (Denmark)
Öztürk, Fatih; Xiao, Sanshui; Yan, Min
2011-01-01
We point out an apparently overlooked consequence of the boundary conditions obeyed by the electric displacement vector at air-metal interfaces: the continuity of the normal component combined with the quantum mechanical penetration of the electron gas in the air implies the existence of a surface...
Plasmon enhanced silver quantum cluster fluorescence for biochemical applications
DEFF Research Database (Denmark)
Bernard, S.; Kutter, J.P.; Mogensen, Klaus Bo
2014-01-01
Fluorescence microscopy of individual silver quantum clusters on the surface of silver nanoparticles reveals strong photoactivated emission under blue light excitation [1-4]. In this work, silver nanoparticles are produced by annealing silver thin films deposited on a glass substrate and silver q...
Kaganskiy, Arsenty; Fischbach, Sarah; Strittmatter, André; Rodt, Sven; Heindel, Tobias; Reitzenstein, Stephan
2018-04-01
We report on the realization of scalable single-photon sources (SPSs) based on single site-controlled quantum dots (SCQDs) and deterministically fabricated microlenses. The fabrication process comprises the buried-stressor growth technique complemented with low-temperature in-situ electron-beam lithography for the integration of SCQDs into microlens structures with high yield and high alignment accuracy. The microlens-approach leads to a broadband enhancement of the photon-extraction efficiency of up to (21 ± 2)% and a high suppression of multi-photon events with g (2)(τ = 0) SPSs which, can be applied in photonic quantum circuits and advanced quantum computation schemes.
Quantum transport in boron-doped nanocrystalline diamond
Czech Academy of Sciences Publication Activity Database
Mareš, Jiří J.; Hubík, Pavel; Krištofik, Jozef; Kindl, Dobroslav; Nesládek, Miloš
2008-01-01
Roč. 14, č. 7-8 (2008), s. 161-172 ISSN 0948-1907 R&D Projects: GA ČR GA202/07/0525; GA AV ČR IAA1010404; GA ČR(CZ) GA202/06/0040 Institutional research plan: CEZ:AV0Z10100521 Keywords : nanocrystalline diamond film * ballistic transport * superconductivity * Josephson’s effects Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.483, year: 2008
Quantum transport in defective phosphorene nanoribbons: Effects of atomic vacancies
Li, L. L.; Peeters, F. M.
2018-02-01
Defects are almost inevitably present in realistic materials and defective materials are expected to exhibit very different properties than their nondefective (perfect) counterparts. Here, using a combination of the tight-binding approach and the scattering matrix formalism, we investigate the electronic transport properties of defective phosphorene nanoribbons (PNRs) containing atomic vacancies. We find that for both armchair PNRs (APNRs) and zigzag PNRs (ZPNRs), single vacancies can create quasilocalized states, which can affect their conductance. With increasing vacancy concentration, three different transport regimes are identified: ballistic, diffusive, and Anderson localized ones. In particular, ZPNRs that are known to be metallic due to the presence of edge states become semiconducting: edge conductance vanishes and transport gap appears due to Anderson localization. Moreover, we find that for a fixed vacancy concentration, both APNRs and ZPNRs of narrower width and/or longer length are more sensitive to vacancy disorder than their wider and/or shorter counterparts, and that for the same ribbon length and width, ZPNRs are more sensitive to vacancy disorder than APNRs.
Optical control of spin-dependent thermal transport in a quantum ring
Abdullah, Nzar Rauf
2018-05-01
We report on calculation of spin-dependent thermal transport through a quantum ring with the Rashba spin-orbit interaction. The quantum ring is connected to two electron reservoirs with different temperatures. Tuning the Rashba coupling constant, degenerate energy states are formed leading to a suppression of the heat and thermoelectric currents. In addition, the quantum ring is coupled to a photon cavity with a single photon mode and linearly polarized photon field. In a resonance regime, when the photon energy is approximately equal to the energy spacing between two lowest degenerate states of the ring, the polarized photon field can significantly control the heat and thermoelectric currents in the system. The roles of the number of photon initially in the cavity, and electron-photon coupling strength on spin-dependent heat and thermoelectric currents are presented.
Macroscopic quantum coherence in a single molecular magnet and Kondo effect of electron transport
International Nuclear Information System (INIS)
Chang, Bo; Wang, Qiang; Xie, Haiqing; Liang, J.-Q.
2011-01-01
We report a Kondo-effect study of electron transport through a quantum dot with embedded biaxial single-molecule magnet based on slave boson mean-field theory and non-equilibrium Green-function technique. It is found the macroscopic quantum coherence of molecule-magnet results in the Kondo peak split of differential conductance due to interaction between electron and molecular magnet. It is also demonstrated that both the peak height and position can be controlled by the sweeping magnetic field and polarization of ferromagnetic electrodes. The characteristic peak split may be used to identify the macroscopic quantum coherence and develop molecule devices. -- Highlights: → Splits of Kondo peak are induced by the single molecular magnet. → Kondo effect can be controlled by magnetic field and its sweeping speed in our model. → The suppression and broadening of Kondo peaks is also observed with increase of temperature. → The peaks height and position is sensitive to polarization of the electrode.
Enhanced quantum efficiency of photoelectron emission, through surface textured metal electrodes
Energy Technology Data Exchange (ETDEWEB)
Alexander, Anna; Bandaru, Prabhakar R., E-mail: pbandaru@ucsd.edu [Program in Materials Science, Department of Mechanical Engineering, University of California, San Diego, La Jolla, California, 92130 (United States); Moody, Nathan A. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2016-03-15
It is predicted that the quantum efficiency (QE) of photoelectron emission from metals may be enhanced, possibly by an order of magnitude, through optimized surface texture. Through extensive computational simulations, it is shown that the absorption enhancement in select surface groove geometries may be a dominant contributor to enhanced QE and corresponds to localized Fabry–Perot resonances. The inadequacy of extant analytical models in predicting the QE increase, and suggestions for further improvement, are discussed.
Quantum field kinetics of QCD: Quark-gluon transport theory for light-cone-dominated processes
International Nuclear Information System (INIS)
Geiger, K.
1996-01-01
A quantum-kinetic formalism is developed to study the dynamical interplay of quantum and statistical-kinetic properties of nonequilibrium multiparton systems produced in high-energy QCD processes. The approach provides the means to follow the quantum dynamics in both space-time and energy-momentum, starting from an arbitrary initial configuration of high-momentum quarks and gluons. Using a generalized functional integral representation and adopting the open-quote open-quote closed-time-path close-quote close-quote Green function techniques, a self-consistent set of equations of motions is obtained: a Ginzburg-Landau equation for a possible color background field, and Dyson-Schwinger equations for the two-point functions of the gluon and quark fields. By exploiting the open-quote open-quote two-scale nature close-quote close-quote of light-cone-dominated QCD processes, i.e., the separation between the quantum scale that specifies the range of short-distance quantum fluctuations, and the kinetic scale that characterizes the range of statistical binary interactions, the quantum field equations of motion are converted into a corresponding set of open-quote open-quote renormalization equations close-quote close-quote and open-quote open-quote transport equations.close-quote close-quote The former describe renormalization and dissipation effects through the evolution of the spectral density of individual, dressed partons, whereas the latter determine the statistical occurrence of scattering processes among these dressed partons. The renormalization equations and the transport equations are coupled, and, hence, must be solved self-consistently. This amounts to evolving the multiparton system, from a specified initial configuration, in time and full seven-dimensional phase space, constrained by the Heisenberg uncertainty principle. (Abstract Truncated)
Grafted organic monolayer for single electron transport and for quantum dots solar cells
Caillard, Louis Marie
Functionalization of oxide-free silicon and silicon oxide surfaces is important for a number of applications. In this work, organic monolayers are grafted (GOM) on oxide-free silicon surfaces using thermal and ultraviolet-activated hydrosilylation of hydrogen-terminated silicon surfaces, primarily using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy for characterization. The resulting amine-terminated GOM have been used for depositing nanoparticles, selecting the end group for two very specific applications: single electron devices and nano-quantum-dot (NQD) enhanced Si photovoltaic cells. To perform single-electron transport measurements, colloidal gold nanoparticles have been deposited on amine-functionalized silicon surfaces and tunneling measurements performed with a scanning tunneling microscope in an ultra-high vacuum chamber. Using a double-barrier tunneling junction (with the GOM as the first barrier and the vacuum between the scanning tip and the gold nanoparticle as the second one), single-electron transport was observed at 30K through a Coulomb staircase phenomenon. The critical parameters were identified to improve reproducibility. Finally, recently developed advanced modeling, based on traditional "orthodox" theory, was optimized to account for the observations (e.g. I-V dependence on band bending). This work provides a basis for the development of single-electron transistors that are compatible with current silicon based technology. To enhance standard silicon-based solar cells, GOM is also needed to graft strongly absorbing II-VI NQDs and optimize their energy transfer to the silicon substrate. Recent photoluminescence spectroscopy has demonstrated that energy transfer occurs through both radiative and non-radiative mechanisms between NQDs and the substrate. With grafting technology, the aim was to optimize absorption, as probed by photoluminescence, in two ways. First, silicon nanopillars were fabricated to increase the
Kirmani, Ahmad R.
2017-07-31
Employment of thin perovskite shells and metal halides as surface-passivants for colloidal quantum dots (CQDs) have been important, recent developments in CQD optoelectronics. These have opened the route to single-step deposited high-performing CQD solar cells. These promising architectures employ a QD hole-transporting layer (HTL) whose intrinsically shallow Fermi level (EF) restricts band-bending at maximum power-point during solar cell operation limiting charge collection. Here, we demonstrate a generalized approach to effectively balance band-edge energy levels of the main CQD absorber and charge-transport layer for these high-performance solar cells. Briefly soaking the QD HTL in a solution of the metal-organic p-dopant, molybdenum tris(1-(trifluoroacetyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), effectively deepens its Fermi level, resulting in enhanced band bending at the HTL:absorber junction. This blocks the back-flow of photo-generated electrons, leading to enhanced photocurrent and fill factor compared to undoped devices. We demonstrate 9.0% perovskite-shelled and 9.5% metal-halide-passivated CQD solar cells, both achieving ca. 10% relative enhancements over undoped baselines.
Nonequilibrium Green's function method for quantum thermal transport
Wang, Jian-Sheng; Agarwalla, Bijay Kumar; Li, Huanan; Thingna, Juzar
2014-12-01
This review deals with the nonequilibrium Green's function (NEGF) method applied to the problems of energy transport due to atomic vibrations (phonons), primarily for small junction systems. We present a pedagogical introduction to the subject, deriving some of the well-known results such as the Laudauer-like formula for heat current in ballistic systems. The main aim of the review is to build the machinery of the method so that it can be applied to other situations, which are not directly treated here. In addition to the above, we consider a number of applications of NEGF, not in routine model system calculations, but in a few new aspects showing the power and usefulness of the formalism. In particular, we discuss the problems of multiple leads, coupled left-right-lead system, and system without a center. We also apply the method to the problem of full counting statistics. In the case of nonlinear systems, we make general comments on the thermal expansion effect, phonon relaxation time, and a certain class of mean-field approximations. Lastly, we examine the relationship between NEGF, reduced density matrix, and master equation approaches to thermal transport.
Novo, Leonardo; Chakraborty, Shantanav; Mohseni, Masoud; Neven, Hartmut; Omar, Yasser
2015-09-01
Continuous time quantum walks provide an important framework for designing new algorithms and modelling quantum transport and state transfer problems. Often, the graph representing the structure of a problem contains certain symmetries that confine the dynamics to a smaller subspace of the full Hilbert space. In this work, we use invariant subspace methods, that can be computed systematically using the Lanczos algorithm, to obtain the reduced set of states that encompass the dynamics of the problem at hand without the specific knowledge of underlying symmetries. First, we apply this method to obtain new instances of graphs where the spatial quantum search algorithm is optimal: complete graphs with broken links and complete bipartite graphs, in particular, the star graph. These examples show that regularity and high-connectivity are not needed to achieve optimal spatial search. We also show that this method considerably simplifies the calculation of quantum transport efficiencies. Furthermore, we observe improved efficiencies by removing a few links from highly symmetric graphs. Finally, we show that this reduction method also allows us to obtain an upper bound for the fidelity of a single qubit transfer on an XY spin network.
Novo, Leonardo; Chakraborty, Shantanav; Mohseni, Masoud; Neven, Hartmut; Omar, Yasser
2015-09-02
Continuous time quantum walks provide an important framework for designing new algorithms and modelling quantum transport and state transfer problems. Often, the graph representing the structure of a problem contains certain symmetries that confine the dynamics to a smaller subspace of the full Hilbert space. In this work, we use invariant subspace methods, that can be computed systematically using the Lanczos algorithm, to obtain the reduced set of states that encompass the dynamics of the problem at hand without the specific knowledge of underlying symmetries. First, we apply this method to obtain new instances of graphs where the spatial quantum search algorithm is optimal: complete graphs with broken links and complete bipartite graphs, in particular, the star graph. These examples show that regularity and high-connectivity are not needed to achieve optimal spatial search. We also show that this method considerably simplifies the calculation of quantum transport efficiencies. Furthermore, we observe improved efficiencies by removing a few links from highly symmetric graphs. Finally, we show that this reduction method also allows us to obtain an upper bound for the fidelity of a single qubit transfer on an XY spin network.
Dependence of enhanced asymmetry-induced transport on collision frequency
International Nuclear Information System (INIS)
Eggleston, D. L.
2014-01-01
A single-particle code with collisional effects is used to study how asymmetry-induced radial transport in a non-neutral plasma depends on collision frequency. For asymmetries of the form ϕ 1 (r) cos(kz) cos(ωt−lθ), two sources for the transport have been identified: resonant particles and axially trapped particles. The simulation shows that this latter type, which occurs near the radius where ω matches the azimuthal rotation frequency ω R , is usually dominant at low collision frequency ν but becomes negligible at higher ν. This behavior can be understood by noting that axially trapped particles have a lower trapping frequency than resonant particles. In the low ν (banana) regime, the radial oscillations have amplitude Δr ≈ v r /ω T , so axially trapped particles dominate, and the transport may even exceed the resonant particle plateau regime level. As ν increases, collisions start to interrupt the slower axially trapped particle oscillations, while the resonant particles are still in the banana regime, so the axially trapped particle contribution to the transport decreases. At the largest ν values, axially trapped particle transport is negligible and the observed diffusion coefficient matches that given by plateau regime resonant particle theory. Heuristic models based on these considerations give reasonable agreement with the observed scaling laws for the value of the collision frequency where axially trapped particle transport starts to decrease and for the enhancement of the diffusion coefficient produced by axially trapped particles
Transport properties of continuous-time quantum walks on Sierpinski fractals.
Darázs, Zoltán; Anishchenko, Anastasiia; Kiss, Tamás; Blumen, Alexander; Mülken, Oliver
2014-09-01
We model quantum transport, described by continuous-time quantum walks (CTQWs), on deterministic Sierpinski fractals, differentiating between Sierpinski gaskets and Sierpinski carpets, along with their dual structures. The transport efficiencies are defined in terms of the exact and the average return probabilities, as well as by the mean survival probability when absorbing traps are present. In the case of gaskets, localization can be identified already for small networks (generations). For carpets, our numerical results indicate a trend towards localization, but only for relatively large structures. The comparison of gaskets and carpets further implies that, distinct from the corresponding classical continuous-time random walk, the spectral dimension does not fully determine the evolution of the CTQW.
Acoustic phonon transport and thermal conductance in a periodically modulated quantum wire
International Nuclear Information System (INIS)
Tang Liming; Wang Lingling; Huang Weiqing; Zou, B S; Chen Keqiu
2007-01-01
We investigate acoustic phonon transport and thermal conductance at low temperatures in a quantum wire with rectangle scatters periodically placed in the quantum channel. It is found that the transmission spectra of zero mode exhibits a series of resonant peaks-valleys structures, and the transport valley gradually develops into stop-frequency gap by increasing the number of the period. The number of resonant peaks or valleys between two nearest gaps is just twice as large as the number of the period. The result also indicates that the thermal conductance is sensitive to the number of the period and structural parameters, and the change is more pronounced in the structure with smaller number of period
Fano interferences in the transport properties of triple quantum dot T-shaped systems
International Nuclear Information System (INIS)
Tifrea, I; Crisan, M; Grosu, I
2009-01-01
We consider the transport and the noise characteristic in the case of a triple quantum dots T-shaped system where two of the dots form a two-level system and the other works in a detector-like setup. Our theoretical results are obtained using the equation of motion method for the case of zero on-site Coulomb interaction in the detector dot. The transport trough the T-shaped system can be controlled by varying the coupling between the two-level system dots or the coupling between the detector dot and the exterior electrodes. The Fano dips in the system's conductance can be observe both for strong (fast detector) and weak coupling (slow detector) between the detector dot and the external electrodes. Due to stronger electronic correlations the noise in the case of a slow detector are much higher. This setup may be of interest for the practical realization of qubit states in quantum dots systems.
Spin-resolved quantum transport in graphene-based nanojunctions
Li, Jian-Wei; Wang, Bin; Yu, Yun-Jin; Wei, Ya-Dong; Yu, Zhi-Zhou; Wang, Yin
2017-08-01
First-principles calculations were performed to explore the spin-resolved electronic and thermoelectric transport properties of a series of graphene-nanoribbon-based nanojunctions. By flipping the magnetic moments in graphene leads from parallel to antiparallel, very large tunneling magnetoresistance can be obtained under different gate voltages for all the structures. Spin-resolved alternating-current conductance increases versus frequency for the short nanojunctions but decreases for the long nanojunctions. With increasing junction length, the behavior of the junctions changes from capacitive-like to inductive-like. Because of the opposite signs of spin-up thermopower and spin-down thermopower near the Fermi level, pure spin currents can be obtained and large figures of merit can be achieved by adjusting the gate voltage and chemical potential for all the nanojunctions.
Zeeman splitting spin filter in a single quantum dot electron transport with Coulomb blockade effect
Lai, Wenxi
2014-01-01
Electron spin filter induced by Zeeman splitting in a few-electron quantum dot coupled to two normal electrodes is studied considering Coulomb blockade effect. Based on the Anderson model and Liouville-von Neumann equation, equation of motion of the system is derived and analytical solutions are achieved. Transport windows for perfectly polarized current, partially polarized current and non-polarized current induced by the Zeeman splitting energy and Coulomb blockade potential are exploited. ...
On the nature of the linewidth enhancement factor in p-doped quantum dash based lasers
International Nuclear Information System (INIS)
Joshi, Siddharth; Chimot, Nicolas; Lelarge, François; Ramdane, Abderrahim
2014-01-01
P-doped quantum dash based lasers have shown superior dynamic performance as compared to their un-doped counterparts. This improvement in performance is strongly observed in line-width enhancement factor. These devices show a dramatic reduction in the α H parameter, resulting in very low chirp. This letter discusses the nature line-width enhancement factor of p-doped quantum dash lasers as opposed to un-doped counterparts. Owing to the p-doping a low and bias-stable alpha parameter is demonstrated
Wu, Feng
2017-05-03
Significant internal quantum efficiency (IQE) enhancement of GaN/AlGaN multiple quantum wells (MQWs) emitting at similar to 350 nm was achieved via a step quantum well (QW) structure design. The MQW structures were grown on AlGaN/AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). High resolution x-ray diffraction (HR-XRD) and scanning transmission electron microscopy (STEM) were performed, showing sharp interface of the MQWs. Weak beam dark field imaging was conducted, indicating a similar dislocation density of the investigated MQWs samples. The IQE of GaN/AlGaN MQWs was estimated by temperature dependent photoluminescence (TDPL). An IQE enhancement of about two times was observed for the GaN/AlGaN step QW structure, compared with conventional QW structure. Based on the theoretical calculation, this IQE enhancement was attributed to the suppressed polarization-induced field, and thus the improved electron-hole wave-function overlap in the step QW.
Makarovsky, Oleg; Turyanska, Lyudmila; Mori, Nobuya; Greenaway, Mark; Eaves, Laurence; Patané, Amalia; Fromhold, Mark; Lara-Avila, Samuel; Kubatkin, Sergey; Yakimova, Rositsa
2017-09-01
We report a simultaneous increase of carrier concentration, mobility and photoresponsivity when SiC-grown graphene is decorated with a surface layer of colloidal PbS quantum dots, which act as electron donors. The charge on the ionised dots is spatially correlated with defect charges on the SiC-graphene interface, thus enhancing both electron carrier density and mobility. This charge-correlation model is supported by Monte Carlo simulations of electron transport and used to explain the unexpected 3-fold increase of mobility with increasing electron density. The enhanced carrier concentration and mobility give rise to Shubnikov-de Haas oscillations in the magnetoresistance, which provide an estimate of the electron cyclotron mass in graphene at high densities and Fermi energies up to 1.2 × 1013 cm-2 and 400 meV, respectively.
Quantum dots for tracking cellular transport of lectin-functionalized nanoparticles
International Nuclear Information System (INIS)
Gao Xiaoling; Wang Tao; Wu Bingxian; Chen Jun; Chen Jiyao; Yue Yang; Dai Ning; Chen Hongzhuan; Jiang Xinguo
2008-01-01
Successful drug delivery by functionalized nanocarriers largely depends on their efficient intracellular transport which has not yet been fully understood. We developed a new tracking technique by encapsulating quantum dots into the core of wheat germ agglutinin-conjugated nanoparticles (WGA-NP) to track cellular transport of functionalized nanocarriers. The resulting nanoparticles showed no changes in particle size, zeta potential or biobinding activity, and the loaded probe presented excellent photostability and tracking ability. Taking advantage of these properties, cellular transport profiles of WGA-NP in Caco-2 cells was demonstrated. The cellular uptake begins with binding of WGA to its receptor at the cell surface. The subsequent endocytosis happened in a cytoskeleton-dependent manner and by means of clathrin and caveolae-mediated mechanisms. After endosome creating, transport occurs to both trans-Golgi and lysosome. Our study provides new evidences for quantum dots as a cellular tracking probe of nanocarriers and helps understand intracellular transport profile of lectin-functionalized nanoparticles
International Nuclear Information System (INIS)
Goswami, Mrinmoy; Ghosh, Ranajit; Maruyama, Takahiro; Meikap, Ajit Kumar
2016-01-01
Graphical abstract: - Highlights: • A new kind of polyaniline/carbon nanotube/CdS quantum dot composites have been synthesized via in-situ polymerization of aniline monomer. • A degree of increase in conductivity. • Size-dependent optical properties of CdS quantum dots have been observed. - Abstract: A new kind of polyaniline/carbon nanotube/CdS quantum dot composites have been developed via in-situ polymerization of aniline monomer in the presence of dispersed CdS quantum dots (size: 2.7–4.8 nm) and multi-walled carbon nanotubes (CNT), which exhibits enhanced optical and electrical properties. The existences of 1st order, 2nd order, and 3rd order longitudinal optical phonon modes, strongly indicate the high quality of synthesized CdS quantum dots. The occurrence of red shift of free exciton energy in photoluminescence is due to size dependent quantum confinement effect of CdS. The conductivity of the composites (for example PANI/CNT/CdS (2 wt.% CdS)) is increased by about 7 of magnitude compared to that of pure PANI indicating a charge transfer between CNT and polymer via CdS quantum dots. This advanced material has a great potential for high-performance of electro-optical applications.
Steepest entropy ascent quantum thermodynamic model of electron and phonon transport
Li, Guanchen; von Spakovsky, Michael R.; Hin, Celine
2018-01-01
An advanced nonequilibrium thermodynamic model for electron and phonon transport is formulated based on the steepest-entropy-ascent quantum thermodynamics framework. This framework, based on the principle of steepest entropy ascent (or the equivalent maximum entropy production principle), inherently satisfies the laws of thermodynamics and mechanics and is applicable at all temporal and spatial scales even in the far-from-equilibrium realm. Specifically, the model is proven to recover the Boltzmann transport equations in the near-equilibrium limit and the two-temperature model of electron-phonon coupling when no dispersion is assumed. The heat and mass transport at a temperature discontinuity across a homogeneous interface where the dispersion and coupling of electron and phonon transport are both considered are then modeled. Local nonequilibrium system evolution and nonquasiequilibrium interactions are predicted and the results discussed.
International Nuclear Information System (INIS)
Zhang, Xiao Li; Dai, Hai Tao; Zhao, Jun Liang; Li, Chen; Wang, Shu Guo; Sun, Xiao Wei
2014-01-01
All-inorganic quantum dot light emitting diodes (QLEDs) have recently gained great attention owing to their high stability under oxygenic, humid environment and higher operating currents. In this work, we fabricated all-inorganic CdSe/ZnS core-shell QLEDs composed of ITO/NiO/QDs/ZnO/Al, in which NiO and ZnO thin film deposited via all-solution method were employed as hole and electron transport layer, respectively. To achieve high light emitting efficiency, the balance transport between electrons and holes play a key role. In this work, the effects of the thickness of NiO film on the performance of QLEDs were explored experimentally in details. NiO layers with various thicknesses were prepared with different rotation speeds. Experimental results showed that thinner NiO layer deposited at higher rotation speed had higher transmittance and larger band gap. Four typical NiO thickness based QLEDs were fabricated to optimize the hole transport layer. Thinner NiO layer based device performs bright emission with high current injection, which is ascribed to the reduced barrier height between hole transport layer and quantum dot. - Highlights: • All-inorganic quantum dot light emitting diodes (QLEDs) were fabricated. • Thinner NiO film can effectively enhance on–off properties of devices. • Improved performance of QLEDs is mainly attributed to energy barrier reduction
Multifunctional superparamagnetic nanoparticles for enhanced drug transport in cystic fibrosis
Armijo, Leisha M.; Brandt, Yekaterina I.; Rivera, Antonio C.; Cook, Nathaniel C.; Plumley, John B.; Withers, Nathan J.; Kopciuch, Michael; Smolyakov, Gennady A.; Huber, Dale L.; Smyth, Hugh D.; Osinski, Marek
2012-10-01
Iron oxide colloidal nanoparticles (ferrofluids) are investigated for application in the treatment of cystic fibrosis lung infections, the leading cause of mortality in cystic fibrosis patients. We investigate the use of iron oxide nanoparticles to increase the effectiveness of administering antibiotics through aerosol inhalation using two mechanisms: directed particle movement in the presence of an inhomogeneous static external magnetic field and magnetic hyperthermia. Magnetic hyperthermia is an effective method for decreasing the viscosity of the mucus and biofilm, thereby enhancing drug, immune cell, and antibody penetration to the affected area. Iron oxide nanoparticles of various sizes and morphologies were synthesized and tested for specific losses (heating power). Nanoparticles in the superparamagnetic to ferromagnetic size range exhibited excellent heating power. Additionally, iron oxide / zinc selenide core/shell nanoparticles were prepared, in order to enable imaging of the iron oxide nanoparticles. We also report on synthesis and characterization of MnSe/ZnSeS alloyed quantum dots.
Quantum Thermodynamics in Strong Coupling: Heat Transport and Refrigeration
Directory of Open Access Journals (Sweden)
Gil Katz
2016-05-01
Full Text Available The performance characteristics of a heat rectifier and a heat pump are studied in a non-Markovian framework. The device is constructed from a molecule connected to a hot and cold reservoir. The heat baths are modelled using the stochastic surrogate Hamiltonian method. The molecule is modelled by an asymmetric double-well potential. Each well is semi-locally connected to a heat bath composed of spins. The dynamics are driven by a combined system–bath Hamiltonian. The temperature of the baths is regulated by a secondary spin bath composed of identical spins in thermal equilibrium. A random swap operation exchange spins between the primary and secondary baths. The combined system is studied in various system–bath coupling strengths. In all cases, the average heat current always flows from the hot towards the cold bath in accordance with the second law of thermodynamics. The asymmetry of the double well generates a rectifying effect, meaning that when the left and right baths are exchanged the heat current follows the hot-to-cold direction. The heat current is larger when the high frequency is coupled to the hot bath. Adding an external driving field can reverse the transport direction. Such a refrigeration effect is modelled by a periodic driving field in resonance with the frequency difference of the two potential wells. A minimal driving amplitude is required to overcome the heat leak effect. In the strong driving regime the cooling power is non-monotonic with the system–bath coupling.
Camjayi, Alberto; Arrachea, Liliana
2014-01-22
We study the transport behavior induced by a small bias voltage through a quantum dot connected to one-channel finite-size wires. We describe the quantum dot using the Hubbard-Anderson impurity model and we obtain solutions by means of a quantum Monte Carlo method. We investigate the effect of a magnetic field applied at the quantum dot in the Kondo regime. We identify mesoscopic oscillations in the conductance, which are introduced by the magnetic field. This behavior is analogous to that observed as a function of the temperature.
Species Distributions, Quantum Theory, and the Enhancement of Biodiversity Measures.
Real, Raimundo; Barbosa, A Márcia; Bull, Joseph W
2017-05-01
Species distributions are typically represented by records of their observed occurrence at a given spatial and temporal scale. Such records are inevitably incomplete and contingent on the spatial-temporal circumstances under which the observations were made. Moreover, organisms may respond differently to similar environmental conditions at different places or moments, so their distribution is, in principle, not completely predictable. We argue that this uncertainty exists, and warrants considering species distributions as analogous to coherent quantum objects, whose distributions are better described by a wavefunction rather than by a set of locations. We use this to extend the existing concept of "dark diversity", which incorporates into biodiversity metrics those species that could, but which have not yet been observed to, inhabit a region-thereby developing the idea of "potential biodiversity". We show how conceptualizing species' distributions in this way could help overcome important weaknesses in current biodiversity metrics, both in theory and by using a worked case study of mammal distributions in Spain over the last decade. We propose that considerable theoretical advances could eventually be gained through interdisciplinary collaboration between biogeographers and quantum physicists. [Biogeography; favorability; physics; predictability; probability; species occurrence; uncertainty; wavefunction. © The Author(s) 2016. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Enhanced round robin CPU scheduling with burst time based time quantum
Indusree, J. R.; Prabadevi, B.
2017-11-01
Process scheduling is a very important functionality of Operating system. The main-known process-scheduling algorithms are First Come First Serve (FCFS) algorithm, Round Robin (RR) algorithm, Priority scheduling algorithm and Shortest Job First (SJF) algorithm. Compared to its peers, Round Robin (RR) algorithm has the advantage that it gives fair share of CPU to the processes which are already in the ready-queue. The effectiveness of the RR algorithm greatly depends on chosen time quantum value. Through this research paper, we are proposing an enhanced algorithm called Enhanced Round Robin with Burst-time based Time Quantum (ERRBTQ) process scheduling algorithm which calculates time quantum as per the burst-time of processes already in ready queue. The experimental results and analysis of ERRBTQ algorithm clearly indicates the improved performance when compared with conventional RR and its variants.
Quantum-dot nano-cavity lasers with Purcell-enhanced stimulated emission
DEFF Research Database (Denmark)
Gregersen, Niels; Skovgård, Troels Suhr; Lorke, Michael
2012-01-01
We present a rate equation model for quantum-dot light-emitting devices that take into account Purcell enhancement of both spontaneous emission and stimulated emission as well as the spectral profile of the optical and electronic density-of-states. We find that below threshold the b-factor in a q...
Transport in constricted quantum Hall systems: beyond the Kane-Fisher paradigm
International Nuclear Information System (INIS)
Lal, Siddhartha
2007-08-01
A simple model of edge transport in a constricted quantum Hall system with a lowered local fi lling factor is studied. The current backscattered from the constriction is explained from a matching of the properties of the edge-current excitations in the constriction (ν 2 ) and bulk (ν 1 ) regions. We develop a hydrodynamic theory for bosonic edge modes inspired by this model, stressing the importance of boundary conditions in elucidating the nature of current transport. By invoking a generalised quasiparticle-quasihole symmetry of the quantum Hall circuit system, we fi nd that a competition between two tunneling process determines the fate of the low-bias transmission conductance. A novel generalisation of the Kane-Fisher quantum impurity model is found, describing transitions from a weak-coupling theory at partial transmission to strong- coupling theories for perfect transmission and reflection as well as a new symmetry dictated fixed point. These results provide satisfactory explanations for recent experimental results at fi lling-factors of 1/3 and 1. (author)
78 FR 53790 - Public Forum-Safety Culture: Enhancing Transportation Safety
2013-08-30
... NATIONAL TRANSPORTATION SAFETY BOARD Public Forum--Safety Culture: Enhancing Transportation Safety On Tuesday and Wednesday, September 10-11, 2013, the National Transportation Safety Board (NTSB) will convene a forum titled, ``Safety Culture: Enhancing Transportation Safety.'' The forum will begin at 9:00...
International Nuclear Information System (INIS)
Ma, Minjie; Jalil, Mansoor Bin Abdul; Tan, Seng Gee
2013-01-01
The spin-dependent transport through a diluted magnetic semiconductor quantum dot (QD) which is coupled via magnetic tunnel junctions to two ferromagnetic leads is studied theoretically. A noncollinear system is considered, where the QD is magnetized at an arbitrary angle with respect to the leads’ magnetization. The tunneling current is calculated in the coherent regime via the Keldysh nonequilibrium Green’s function (NEGF) formalism, incorporating the electron–electron interaction in the QD. We provide the first analytical solution for the Green’s function of the noncollinear DMS quantum dot system, solved via the equation of motion method under Hartree–Fock approximation. The transport characteristics (charge and spin currents, and tunnel magnetoresistance (TMR)) are evaluated for different voltage regimes. The interplay between spin-dependent tunneling and single-charge effects results in three distinct voltage regimes in the spin and charge current characteristics. The voltage range in which the QD is singly occupied corresponds to the maximum spin current and greatest sensitivity of the spin current to the QD magnetization orientation. The QD device also shows transport features suitable for sensor applications, i.e., a large charge current coupled with a high TMR ratio. - Highlights: ► The spin polarized transport through a diluted magnetic quantum dot is studied. ► The model is based on the Green’s function and the equation of motion method.► The charge and spin currents and tunnel magnetoresistance (TMR) are investigated. ► The system is suitable for current-induced spin-transfer torque application. ► A large tunneling current and a high TMR are possible for sensor application.
Quantum-Enhanced Reinforcement Learning for Finite-Episode Games with Discrete State Spaces
Directory of Open Access Journals (Sweden)
Florian Neukart
2018-02-01
Full Text Available Quantum annealing algorithms belong to the class of metaheuristic tools, applicable for solving binary optimization problems. Hardware implementations of quantum annealing, such as the quantum annealing machines produced by D-Wave Systems [1], have been subject to multiple analyses in research, with the aim of characterizing the technology's usefulness for optimization and sampling tasks [2–16]. Here, we present a way to partially embed both Monte Carlo policy iteration for finding an optimal policy on random observations, as well as how to embed n sub-optimal state-value functions for approximating an improved state-value function given a policy for finite horizon games with discrete state spaces on a D-Wave 2000Q quantum processing unit (QPU. We explain how both problems can be expressed as a quadratic unconstrained binary optimization (QUBO problem, and show that quantum-enhanced Monte Carlo policy evaluation allows for finding equivalent or better state-value functions for a given policy with the same number episodes compared to a purely classical Monte Carlo algorithm. Additionally, we describe a quantum-classical policy learning algorithm. Our first and foremost aim is to explain how to represent and solve parts of these problems with the help of the QPU, and not to prove supremacy over every existing classical policy evaluation algorithm.
Quantum-enhanced reinforcement learning for finite-episode games with discrete state spaces
Neukart, Florian; Von Dollen, David; Seidel, Christian; Compostella, Gabriele
2017-12-01
Quantum annealing algorithms belong to the class of metaheuristic tools, applicable for solving binary optimization problems. Hardware implementations of quantum annealing, such as the quantum annealing machines produced by D-Wave Systems, have been subject to multiple analyses in research, with the aim of characterizing the technology's usefulness for optimization and sampling tasks. Here, we present a way to partially embed both Monte Carlo policy iteration for finding an optimal policy on random observations, as well as how to embed n sub-optimal state-value functions for approximating an improved state-value function given a policy for finite horizon games with discrete state spaces on a D-Wave 2000Q quantum processing unit (QPU). We explain how both problems can be expressed as a quadratic unconstrained binary optimization (QUBO) problem, and show that quantum-enhanced Monte Carlo policy evaluation allows for finding equivalent or better state-value functions for a given policy with the same number episodes compared to a purely classical Monte Carlo algorithm. Additionally, we describe a quantum-classical policy learning algorithm. Our first and foremost aim is to explain how to represent and solve parts of these problems with the help of the QPU, and not to prove supremacy over every existing classical policy evaluation algorithm.
Enhanced quantum spin fluctuations in a binary Bose-Einstein condensate
Bisset, R. N.; Kevrekidis, P. G.; Ticknor, C.
2018-02-01
For quantum fluids, the role of quantum fluctuations may be significant in several regimes such as when the dimensionality is low, the density is high, the interactions are strong, or for low particle numbers. In this paper, we propose a fundamentally different regime for enhanced quantum fluctuations without being restricted by any of the above conditions. Instead, our scheme relies on the engineering of an effective attractive interaction in a dilute, two-component Bose-Einstein condensate (BEC) consisting of thousands of atoms. In such a regime, the quantum spin fluctuations are significantly enhanced (atom bunching with respect to the noninteracting limit) since they act to reduce the interaction energy, a remarkable property given that spin fluctuations are normally suppressed (antibunching) at zero temperature. In contrast to the case of true attractive interactions, our approach is not vulnerable to BEC collapse. We numerically demonstrate that these quantum fluctuations are experimentally accessible by either spin or single-component Bragg spectroscopy, offering a useful platform on which to test beyond-mean-field theories. We also develop a variational model and use it to analytically predict the shift of the immiscibility critical point, finding good agreement with our numerics.
Continuous-time quantum walks: Models for coherent transport on complex networks
Energy Technology Data Exchange (ETDEWEB)
Muelken, Oliver, E-mail: muelken@physik.uni-freiburg.de; Blumen, Alexander
2011-05-15
This paper reviews recent advances in continuous-time quantum walks (CTQW) and their application to transport in various systems. The introduction gives a brief survey of the historical background of CTQW. After a short outline of the theoretical ideas behind CTQW and of its relation to classical continuous-time random walks (CTRW), implications for the efficiency of the transport are presented. This paper gives an overview of different types of networks on which CTQW have been studied so far. Extensions of CTQW to systems with long-range interactions and with static disorder are also discussed. Systems with traps, i.e., systems in which a walker's probability to remain inside the system is not conserved, are presented. Relations to similar approaches to the transport are studied. This paper closes with an outlook on possible future directions.
Zamani Siboni, Hossein; Sadeghimakki, Bahareh; Sivoththaman, Siva; Aziz, Hany
2015-11-25
We demonstrate very efficient and bright quantum dot light-emitting devices (QDLEDs) with the use of a phosphorescent sensitizer and a thermal annealing step. Utilizing CdSe/CdS core/shell quantum dots with 560 nm emission peak, bis(4,6-difluorophenylpyridinatoN,C2) picolinatoiridium as a sensitizer, and thermal annealing at 50 °C for 30 min, green-emitting QDLEDs with a maximum current efficiency of 23.9 cd/A, a power efficiency of 31 lm/W, and a brightness of 65,000 cd/m(2) are demonstrated. The high efficiency and brightness are attributed to annealing-induced enhancements in both the Forster resonance energy transfer (FRET) process from the phosphorescent energy donor to the QD acceptor and hole transport across the device. The FRET enhancement is attributed to annealing-induced diffusion of the phosphorescent material molecules from the sensitizer layer into the QD layer, which results in a shorter donor-acceptor distance. We also find, quite interestingly, that FRET to a QD acceptor is strongly influenced by the QD size, and is generally less efficient to QDs with larger sizes despite their narrower bandgaps.
Labelle, A. J.
2017-02-03
The engineering of broadband absorbers to harvest white light in thin-film semiconductors is a major challenge in developing renewable materials for energy harvesting. Many solution-processed materials with high manufacturability and low cost, such as semiconductor quantum dots, require the use of film structures with thicknesses on the order of 1 μm to absorb incoming photons completely. The electron transport lengths in these media, however, are 1 order of magnitude smaller than this length, hampering further progress with this platform. Herein, we show that, by engineering suitably disordered nanoplasmonic structures, we have created a new class of dispersionless epsilon-near-zero composite materials that efficiently harness white light. Our nanostructures localize light in the dielectric region outside the epsilon-near-zero material with characteristic lengths of 10-100 nm, resulting in an efficient system for harvesting broadband light when a thin absorptive film is deposited on top of the structure. By using a combination of theory and experiments, we demonstrate that ultrathin layers down to 50 nm of colloidal quantum dots deposited atop the epsilon-near-zero material show an increase in broadband absorption ranging from 200% to 500% compared to a planar structure of the same colloidal quantum-dot-absorber average thickness. When the epsilon-near-zero nanostructures were used in an energy-harvesting module, we observed a spectrally averaged 170% broadband increase in the external quantum efficiency of the device, measured at wavelengths between 400 and 1200 nm. Atomic force microscopy and photoluminescence excitation measurements demonstrate that the properties of these epsilon-near-zero structures apply to general metals and could be used to enhance the near-field absorption of semiconductor structures more widely. We have developed an inexpensive electrochemical deposition process that enables scaled-up production of this nanomaterial for large
Energy Technology Data Exchange (ETDEWEB)
Brogi, Bharat Bhushan, E-mail: brogi-221179@yahoo.in; Ahluwalia, P. K. [Department of Physics, Himachal Pradesh University, Shimla-171005 (India); Chand, Shyam [University Institute of Information Technology, H.P. University Shimla-171005 (India)
2015-06-24
Theoretical study of the Coulomb blockade effect on transport properties (Transmission Probability and I-V characteristics) for varied configuration of coupled quantum dot system has been studied by using Non Equilibrium Green Function(NEGF) formalism and Equation of Motion(EOM) method in the presence of magnetic flux. The self consistent approach and intra-dot Coulomb interaction is being taken into account. As the key parameters of the coupled quantum dot system such as dot-lead coupling, inter-dot tunneling and magnetic flux threading through the system can be tuned, the effect of asymmetry parameter and magnetic flux on this tuning is being explored in Coulomb blockade regime. The presence of the Coulomb blockade due to on-dot Coulomb interaction decreases the width of transmission peak at energy level ε + U and by adjusting the magnetic flux the swapping effect in the Fano peaks in asymmetric and symmetric parallel configuration sustains despite strong Coulomb blockade effect.
Stochastic quantum thermodynamics, entropy production, and transport properties of a bosonic system
de Oliveira, Mário J.
2018-01-01
The transport properties of a bosonic chain have been calculated by placing the ends of the chain in contact with thermal and particle reservoirs at different temperatures and chemical potentials. The contact with the reservoirs is described by the use of a quantum Fokker-Planck-Kramers equation, which is a canonical quantization of the classical Fokker-Planck-Kramers equation. From the quantum equation we obtain equations for the covariances of the creation and annihilation boson operators and solve them in the stationary state for small interactions. From the covariances we determine the Onsager coefficients and in particular the conductance, which was found to be finite for any chain size leading to an infinite conductivity and the absence of Fourier's law.
Resonantly enhanced tunneling and transport of ultracold atoms on tilted optical lattices
Energy Technology Data Exchange (ETDEWEB)
Rubbo, Chester P.; Manmana, Salvatore R.; Peden, Brandon M.; Holland, Murray J.; Rey, Ana Maria [JILA (NIST and University of Colorado) and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440 (United States)
2011-09-15
We investigate the resonantly enhanced tunneling dynamics of ultracold bosons loaded on a tilted one-dimensional optical lattice, which can be used to simulate a chain of Ising spins and associated quantum phase transitions. The center-of-mass motion after a sudden tilt both at commensurate and incommensurate fillings is obtained via analytic, time-dependent exact diagonalization and density-matrix renormalization-group methods. We identify a maximum in the amplitude of the center-of-mass oscillations at the quantum critical point of the effective spin system. For the dynamics of incommensurate systems, which cannot be mapped to a spin model, we develop an analytical approach in which the time evolution is obtained by projecting onto resonant families of small clusters. We compare the results of this approach at low fillings to the exact time evolution and find good agreement even at filling factors as large as 2/3. Using this projection onto small clusters, we propose a controllable transport scheme applicable in the context of Atomtronic devices on optical lattices (''slinky scheme'').
Resonantly enhanced tunneling and transport of ultracold atoms on tilted optical lattices
International Nuclear Information System (INIS)
Rubbo, Chester P.; Manmana, Salvatore R.; Peden, Brandon M.; Holland, Murray J.; Rey, Ana Maria
2011-01-01
We investigate the resonantly enhanced tunneling dynamics of ultracold bosons loaded on a tilted one-dimensional optical lattice, which can be used to simulate a chain of Ising spins and associated quantum phase transitions. The center-of-mass motion after a sudden tilt both at commensurate and incommensurate fillings is obtained via analytic, time-dependent exact diagonalization and density-matrix renormalization-group methods. We identify a maximum in the amplitude of the center-of-mass oscillations at the quantum critical point of the effective spin system. For the dynamics of incommensurate systems, which cannot be mapped to a spin model, we develop an analytical approach in which the time evolution is obtained by projecting onto resonant families of small clusters. We compare the results of this approach at low fillings to the exact time evolution and find good agreement even at filling factors as large as 2/3. Using this projection onto small clusters, we propose a controllable transport scheme applicable in the context of Atomtronic devices on optical lattices (''slinky scheme'').
Resonantly enhanced tunneling and transport of ultracold atoms on tilted optical lattices
Rubbo, Chester P.; Manmana, Salvatore R.; Peden, Brandon M.; Holland, Murray J.; Rey, Ana Maria
2011-09-01
We investigate the resonantly enhanced tunneling dynamics of ultracold bosons loaded on a tilted one-dimensional optical lattice, which can be used to simulate a chain of Ising spins and associated quantum phase transitions. The center-of-mass motion after a sudden tilt both at commensurate and incommensurate fillings is obtained via analytic, time-dependent exact diagonalization and density-matrix renormalization-group methods. We identify a maximum in the amplitude of the center-of-mass oscillations at the quantum critical point of the effective spin system. For the dynamics of incommensurate systems, which cannot be mapped to a spin model, we develop an analytical approach in which the time evolution is obtained by projecting onto resonant families of small clusters. We compare the results of this approach at low fillings to the exact time evolution and find good agreement even at filling factors as large as 2/3. Using this projection onto small clusters, we propose a controllable transport scheme applicable in the context of Atomtronic devices on optical lattices (“slinky scheme”).
A GaAs-based up-converter for mid-infrared detection utilizing quantum cascade transport
Hao, Zhibiao; Xie, Lili; Wang, Chao; Liu, Yaqi; Wang, Lai; Wang, Jian; Xiong, Bing; Sun, Changzheng; Han, Yanjun; Li, Hongtao; Luo, Yi
2017-08-01
The next generation infrared (IR) detection technology demands for very-large-format focal plane arrays (FPAs) with high performance. Semiconductor up-converters can convert IR photons to near-infrared (NIR) photons, and can be potential candidates for large-format IR imaging since the mechanical bonding with the read-out circuits can be avoided. However, previously reported up-converters and corresponding up-conversion systems suffer from low detectivity because of the trade-off between responsivity and dark current. To solve this issue, a cascade infrared up-converter (CIUP) is demonstrated in this work. Based on a quantum cascade transport mechanism, high IR responsivity is achieved while the dark current is maintained fairly low. A 4-μm InGaAs/AlGaAs CIUP has been fabricated, and both the CIUP and up-conversion system are under background-limited infrared performance (BLIP) regime below 120 K. The upconversion efficiency is 2.1 mW/W at 3.3 V and 78 K. Taking shot noise as the main noise in the up-conversion system, the BLIP detectivity of the system is 2.4×109 Jones at 3.3 V and 78 K, higher than the semiconductor up-converters at similar wavelengths reported so far. To further improve the CIUP performance, an AlInP hole-blocking layer is introduced taking place of the AlAs layer. AlInP/GaAs has larger valence band discontinuity than AlAs/GaAs, showing the advantage of tightly confining injected holes into the emission quantum well. By adopting the AlInP hole-blocking layer, the quantum efficiency and detectivity of the up-conversion system can be enhanced.
Transport analysis of pellet-enhanced ICRH plasma in JET
International Nuclear Information System (INIS)
Hammett, G.W.; Colestock, P.L.; Granetz, R.S.; McCune, D.C.; Phillips, C.K.; Schmidt, G.L.; Smithe, D.N.; Kupschus, P.
1989-01-01
Performance of JET ICRH heated discharges has been significantly enhanced by using pellet fueling to produce a peaked density target for ICRH. The central T i is observed to increase by up to 80%, central T e by up to 40%, and the neutron rate by up to 400%, over their no-pellet values (which are already in the enhanced 'monster-sawtooth' regime). In this paper we describe the transport analysis of these discharges using the TRANSP code. These results indicate that the thermal diffusivities χ i and χ e are reduced by a factor of ∼2 near the plasma center where the pellets have increased the density gradient. The paper focuses on JET discharge 16211 which is documented more fully in a companion paper. (author) 6 refs., 8 figs
Irradiation-enhanced and-induced mass transport
International Nuclear Information System (INIS)
Rehn, L.E.
1989-01-01
Irradiation can be used to enhance diffusion, that is, to increase the rate at which equilibrium is attained, as well as to induce nonequilibrium changes. The main factors influencing whether irradiation will drive a material toward or away from equilibrium are the initial specimen microstructure and geometry, irradiation temperature, and primary recoil spectrum. This paper summarizes known effects of irradiation temperature and primary recoil spectrum on mass transport during irradiation. In comparison to either electron or heavy-ion irradiation, it is concluded that relatively low-energy, light-ion bombardment at intermediate temperatures offers the greatest potential to enhance the rate at which equilibrium is attained. The greatest departures from equilibrium can be expected from irradiation with similar particles at very low temperatures
Conductance enhancement in quantum-point-contact semiconductor-superconductor devices
DEFF Research Database (Denmark)
Mortensen, Asger; Jauho, Antti-Pekka; Flensberg, Karsten
1999-01-01
We present numerical calculations of the conductance of an interface between a phase-coherent two-dimensional electron gas and a superconductor with a quantum point contact in the normal region. Using a scattering matrix approach we reconsider the geometry of De Raedt, Michielsen, and Klapwijk...... [Phys. Rev. B 50, 631 (1994)] which was studied within the time-dependent Bogoliubov-de Gennes formalism. We find that the factor-of-2 enhancement of the conductance G(NS) compared to the normal state conductance GN for ideal interfaces may be suppressed for interfaces with a quantum point contact...
Querlioz, Damien
2013-01-01
This book gives an overview of the quantum transport approaches for nanodevices and focuses on the Wigner formalism. It details the implementation of a particle-based Monte Carlo solution of the Wigner transport equation and how the technique is applied to typical devices exhibiting quantum phenomena, such as the resonant tunnelling diode, the ultra-short silicon MOSFET and the carbon nanotube transistor. In the final part, decoherence theory is used to explain the emergence of the semi-classical transport in nanodevices.
Quantum transport in GaN/AlN double-barrier heterostructure nanowires.
Songmuang, R; Katsaros, G; Monroy, E; Spathis, P; Bougerol, C; Mongillo, M; De Franceschi, S
2010-09-08
We investigate electronic transport in n-i-n GaN nanowires with and without AlN double barriers. The nanowires are grown by catalyst-free, plasma-assisted molecular beam epitaxy enabling abrupt GaN/AlN interfaces as well as longitudinal n-type doping modulation. At low temperature, transport in n-i-n GaN nanowires is dominated by the Coulomb blockade effect. Carriers are confined in the undoped middle region, forming single or multiple islands with a characteristic length of approximately 100 nm. The incorporation of two AlN tunnel barriers causes confinement to occur within the GaN dot in between. In the case of a 6 nm thick dot and 2 nm thick barriers, we observe characteristic signatures of Coulomb-blockaded transport in single quantum dots with discrete energy states. For thinner dots and barriers, Coulomb-blockade effects do not play a significant role while the onset of resonant tunneling via the confined quantum levels is accompanied by a negative differential resistance surviving up to approximately 150 K.
Jacob, D; Palacios, J J
2011-01-28
We study the performance of two different electrode models in quantum transport calculations based on density functional theory: parametrized Bethe lattices and quasi-one-dimensional wires or nanowires. A detailed account of implementation details in both the cases is given. From the systematic study of nanocontacts made of representative metallic elements, we can conclude that the parametrized electrode models represent an excellent compromise between computational cost and electronic structure definition as long as the aim is to compare with experiments where the precise atomic structure of the electrodes is not relevant or defined with precision. The results obtained using parametrized Bethe lattices are essentially similar to the ones obtained with quasi-one-dimensional electrodes for large enough cross-sections of these, adding a natural smearing to the transmission curves that mimics the true nature of polycrystalline electrodes. The latter are more demanding from the computational point of view, but present the advantage of expanding the range of applicability of transport calculations to situations where the electrodes have a well-defined atomic structure, as is the case for carbon nanotubes, graphene nanoribbons, or semiconducting nanowires. All the analysis is done with the help of codes developed by the authors which can be found in the quantum transport toolbox ALACANT and are publicly available.
Oxygen transport enhancement by functionalized magnetic nanoparticles (FMP) in bioprocesses
Ataide, Filipe Andre Prata
The enhancement of fluid properties, namely thermal conductivity and mass diffusivity for a wide range of applications, through the use of nanosized particles' suspensions has been gathering increasing interest in the scientific community. In previous studies, Olle et al. (2006) showed an enhancement in oxygen absorption to aqueous solutions of up to 6-fold through the use of functionalized nanosized magnetic particles with oleic acid coating. Krishnamurthy et al. (2006) showed a remarkable 26-fold enhancement in dye diffusion in water. These two publications are landmarks in mass transfer enhancement in chemical systems through the use of nanoparticles. The central goal of this Ph.D. thesis was to develop functionalized magnetic nanoparticles to enhance oxygen transport in bioprocesses. The experimental protocol for magnetic nanoparticles synthesis and purification adopted in this thesis is a modification of that reported by Olle et al. (2006). This is facilitated by employing twice the quantity of ammonia, added at a slower rate, and by filtering the final nanoparticle solution in a cross-flow filtration modulus against 55 volumes of distilled water. This modification in the protocol resulted in improved magnetic nanoparticles with measurably higher mass transfer enhancement. Magnetic nanoparticles with oleic acid and Hitenol-BC coating were screened for oxygen transfer enhancement, since these particles are relatively inexpensive and easy to synthesize. A glass 0.5-liter reactor was custom manufactured specifically for oxygen transport studies in magnetic nanoparticles suspensions. The reactor geometry, baffles and Rushton impeller are of standard dimensions. Mass transfer tests were conducted through the use of the sulphite oxidation method, applying iodometric back-titration. A 3-factor central composite circumscribed design (CCD) was adopted for design of experiments in order to generate sufficiently informative data to model the effect of magnetic
Al-Khalili, Jim
2003-01-01
In this lively look at quantum science, a physicist takes you on an entertaining and enlightening journey through the basics of subatomic physics. Along the way, he examines the paradox of quantum mechanics--beautifully mathematical in theory but confoundingly unpredictable in the real world. Marvel at the Dual Slit experiment as a tiny atom passes through two separate openings at the same time. Ponder the peculiar communication of quantum particles, which can remain in touch no matter how far apart. Join the genius jewel thief as he carries out a quantum measurement on a diamond without ever touching the object in question. Baffle yourself with the bizzareness of quantum tunneling, the equivalent of traveling partway up a hill, only to disappear then reappear traveling down the opposite side. With its clean, colorful layout and conversational tone, this text will hook you into the conundrum that is quantum mechanics.
Solar Cells Using Quantum Funnels
Kramer, Illan J.
2011-09-14
Colloidal quantum dots offer broad tuning of semiconductor bandstructure via the quantum size effect. Devices involving a sequence of layers comprised of quantum dots selected to have different diameters, and therefore bandgaps, offer the possibility of funneling energy toward an acceptor. Here we report a quantum funnel that efficiently conveys photoelectrons from their point of generation toward an intended electron acceptor. Using this concept we build a solar cell that benefits from enhanced fill factor as a result of this quantum funnel. This concept addresses limitations on transport in soft condensed matter systems and leverages their advantages in large-area optoelectronic devices and systems. © 2011 American Chemical Society.
Selective recognition of Glutamate based on fluorescence enhancement of graphene quantum dot.
Hosseini, Morteza; Khabbaz, Hossein; Dezfoli, Amin Shiralizadeh; Ganjali, Mohammad Reza; Dadmehr, Mehdi
2015-02-05
Graphene quantum dots (GQDs) have successfully been utilized as an efficient nano-sized fluorescence chemosensor to detect selectively Glutamate (Glu) in Tris-HCl buffer solution (pH=9). The fluorescence emission spectrum of graphene quantum dots was at about 430nm. The study showed that fluorescence intensity of the quantum dot gradually enhanced with increase in concentration of Glutamate and any change in fluorescence intensity was directly proportional to the concentration of Glutamate. Under optimum conditions, the linear range for the detection of Glutamate was 1.6×10(-7)M to 1.0×10(-5)M with a detection limit of 5.2×10(-8)M. The sensor showed high selectivity toward Glutamate in comparison with other amino acids. Copyright © 2014 Elsevier B.V. All rights reserved.
Quantum transport through complex networks - from light-harvesting proteins to semiconductor devices
Energy Technology Data Exchange (ETDEWEB)
Kreisbeck, Christoph
2012-06-18
Electron transport through small systems in semiconductor devices plays an essential role for many applications in micro-electronics. One focus of current research lies on establishing conceptually new devices based on ballistic transport in high mobility AlGaAs/AlGa samples. In the ballistic regime, the transport characteristics are determined by coherent interference effects. In order to guide experimentalists to an improved device design, the characterization and understanding of intrinsic device properties is crucial. We develop a time-dependent approach that allows us to simulate experimentally fabricated, complex devicegeometries with an extension of up to a few micrometers. Particularly, we explore the physical origin of unexpected effects that have been detected in recent experiments on transport through Aharonov-Bohm waveguide-interferometers. Such interferometers can be configured as detectors for transfer properties of embedded quantum systems. We demonstrate that a four-terminal waveguide-ring is a suitable setup for measuring the transmission phase of a harmonic quantum dot. Quantum effects are not restricted exclusively to artificial devices but have been found in biological systems as well. Pioneering experiments reveal quantum effects in light-harvesting complexes, the building blocks of photosynthesis. We discuss the Fenna-Matthews-Olson complex, which is a network of coupled bacteriochlorophylls. It acts as an energy wire in the photosynthetic apparatus of green sulfur bacteria. Recent experimental findings suggest that energy transfer takes place in the form of coherent wave-like motion, rather than through classical hopping from one bacteriochlorophyll to the next. However, the question of why and how coherent transfer emerges in light-harvesting complexes is still open. The challenge is to merge seemingly contradictory features that are observed in experiments on two-dimensional spectroscopy into a consistent theory. Here, we provide such a
Simulations of quantum transport in nanoscale systems: application to atomic gold and silver wires
DEFF Research Database (Denmark)
Mozos, J.L.; Ordejon, P.; Brandbyge, Mads
2002-01-01
. The potential drop profile and induced electronic current (and therefore the conductance) are obtained from first principles. The method takes into account the atomic structure of both the nanoscale structure and the semi-infinite electrodes through which the potential is applied. Non-equilibrium Green......'s function techniques are used to calculate the quantum conductance. Here we apply the method to the study of the electronic transport in wires of gold and silver with atomic thickness. We show the results of our calculations, and compare with some of the abundant experimental data on these systems....
Inelastic quantum transport and peierls-like mechanism in carbon nanotubes.
Foa Torres, Luis E F; Roche, Stephan
2006-08-18
We report on a theoretical study of inelastic quantum transport in (3m,0) carbon nanotubes. By using a many-body description of the electron-phonon interaction in Fock space, a novel mechanism involving optical phonon emission (absorption) is shown to induce an unprecedented energy-gap opening at half the phonon energy, variant Planck's over 2piomega0/2, above (below) the charge neutrality point. This mechanism, which is prevented by Pauli blocking at low bias voltages, is activated at bias voltages on the order of variant Planck's over 2piomega0.
An approximate framework for quantum transport calculation with model order reduction
Energy Technology Data Exchange (ETDEWEB)
Chen, Quan, E-mail: quanchen@eee.hku.hk [Department of Electrical and Electronic Engineering, The University of Hong Kong (Hong Kong); Li, Jun [Department of Chemistry, The University of Hong Kong (Hong Kong); Yam, Chiyung [Beijing Computational Science Research Center (China); Zhang, Yu [Department of Chemistry, The University of Hong Kong (Hong Kong); Wong, Ngai [Department of Electrical and Electronic Engineering, The University of Hong Kong (Hong Kong); Chen, Guanhua [Department of Chemistry, The University of Hong Kong (Hong Kong)
2015-04-01
A new approximate computational framework is proposed for computing the non-equilibrium charge density in the context of the non-equilibrium Green's function (NEGF) method for quantum mechanical transport problems. The framework consists of a new formulation, called the X-formulation, for single-energy density calculation based on the solution of sparse linear systems, and a projection-based nonlinear model order reduction (MOR) approach to address the large number of energy points required for large applied biases. The advantages of the new methods are confirmed by numerical experiments.
Valley-polarized quantum transport generated by gauge fields in graphene
DEFF Research Database (Denmark)
Settnes, Mikkel; Garcia, Jose H; Roche, Stephan
2017-01-01
We report on the possibility to simultaneously generate in graphene a bulk valley-polarized dissipative transport and a quantum valley Hall effect by combining strain-induced gauge fields and real magnetic fields. Such unique phenomenon results from a ‘resonance/anti-resonance’ effect driven...... by the superposition/cancellation of superimposed gauge fields which differently affect time reversal symmetry. The onset of a valley-polarized Hall current concomitant to a dissipative valley-polarized current flow in the opposite valley is revealed by a Hall conductivity plateau. We employ efficient linear scaling...
Cellular Uptake Properties of the Complex Derived from Quantum Dots and G8 Molecular Transporter
International Nuclear Information System (INIS)
Im, Jung Kyun; Maiti, Kaustabh K.; Kim, Wan Il; Kim, Kyong Tai; Chung, Sung Kee
2011-01-01
The biotin-attached G8 molecular transporter (5) was synthesized and used together with quantum dots in preparing the complexes (QD-MT). The QD-MT complexes were studied in terms of the cellular uptake and the internalization mechanism in live HeLa cells with the aid of various known endocytosis inhibitors. It has been concluded that the QD-MT complex is internalized largely by macropinocytosis. The mouse tissue distribution of the QD-MT complex by i.p. and i.v. routes showed some organ selectivity and a good ability to cross the BBB
Cellular Uptake Properties of the Complex Derived from Quantum Dots and G8 Molecular Transporter
Energy Technology Data Exchange (ETDEWEB)
Im, Jung Kyun; Maiti, Kaustabh K.; Kim, Wan Il; Kim, Kyong Tai; Chung, Sung Kee [Pohang University of Science and Technology, Pohang (Korea, Republic of)
2011-04-15
The biotin-attached G8 molecular transporter (5) was synthesized and used together with quantum dots in preparing the complexes (QD-MT). The QD-MT complexes were studied in terms of the cellular uptake and the internalization mechanism in live HeLa cells with the aid of various known endocytosis inhibitors. It has been concluded that the QD-MT complex is internalized largely by macropinocytosis. The mouse tissue distribution of the QD-MT complex by i.p. and i.v. routes showed some organ selectivity and a good ability to cross the BBB.
Directory of Open Access Journals (Sweden)
A. Jamshidi
2015-01-01
Full Text Available Colloidal Mn-doped ZnSe/CdS core/shell quantum dots (QDs are synthesized for the first time and employed as a strategy to boost the power conversion efficiency of quantum dot sensitized solar cells. By using Mn-doping as a band gap engineering tool for core/shell QDs an effective improvement of absorption spectra could be obtained. The mid-states generated by a proper Mn content alleviate carrier separation and enhance the electron injection rate, thus facilitating electron transport to the TiO2 substrate. It is demonstrated that a device constructed with 0.25% Mn-doped ZnSe/CdS leads to an enhancement of the electron injection rate and power conversion efficiency by 4 times and 1.3, respectively.
Plasmonic photocatalytic reactions enhanced by hot electrons in a one-dimensional quantum well
Directory of Open Access Journals (Sweden)
H. J. Huang
2015-11-01
Full Text Available The plasmonic endothermic oxidation of ammonium ions in a spinning disk reactor resulted in light energy transformation through quantum hot charge carriers (QHC, or quantum hot electrons, during a chemical reaction. It is demonstrated with a simple model that light of various intensities enhance the chemical oxidization of ammonium ions in water. It was further observed that light illumination, which induces the formation of plasmons on a platinum (Pt thin film, provided higher processing efficiency compared with the reaction on a bare glass disk. These induced plasmons generate quantum hot electrons with increasing momentum and energy in the one-dimensional quantum well of a Pt thin film. The energy carried by the quantum hot electrons provided the energy needed to catalyze the chemical reaction. The results indicate that one-dimensional confinement in spherical coordinates (i.e., nanoparticles is not necessary to provide an extra excited state for QHC generation; an 8 nm Pt thin film for one-dimensional confinement in Cartesian coordinates can also provide the extra excited state for the generation of QHC.
Long-range transport in excitonic dark states in coupled quantum wells.
Snoke, D; Denev, S; Liu, Y; Pfeiffer, L; West, K
2002-08-15
During the past ten years, coupled quantum wells have emerged as a promising system for experiments on Bose condensation of excitons, with numerous theoretical and experimental studies aimed at the demonstration of this effect. One of the issues driving these studies is the possibility of long-range coherent transport of excitons. Excitons in quantum wells typically diffuse only a few micrometres from the spot where they are generated by a laser pulse; their diffusion is limited by their lifetime (typically a few nanoseconds) and by scattering due to disorder in the well structure. Here we report photoluminescence measurements of InGaAs quantum wells and the observation of an effect by which luminescence from excitons appears hundreds of micrometres away from the laser excitation spot. This luminescence appears as a ring around the laser spot; almost none appears in the region between the laser spot and the ring. This implies that the excitons must travel in a dark state until they reach some critical distance, at which they collectively revert to luminescing states. It is unclear whether this effect is related to macroscopic coherence caused by Bose condensation of excitons.
Chatterjee, Shubhayu; Sachdev, Subir; Eberlein, Andreas
2017-08-01
We study thermal and electrical transport in metals and superconductors near a quantum phase transition where antiferromagnetic order disappears. The same theory can also be applied to quantum phase transitions involving the loss of certain classes of intrinsic topological order. For a clean superconductor, we recover and extend well-known universal results. The heat conductivity for commensurate and incommensurate antiferromagnetism coexisting with superconductivity shows a markedly different doping dependence near the quantum critical point, thus allowing us to distinguish between these states. In the dirty limit, the results for the conductivities are qualitatively similar for the metal and the superconductor. In this regime, the geometric properties of the Fermi surface allow for a very good phenomenological understanding of the numerical results on the conductivities. In the simplest model, we find that the conductivities do not track the doping evolution of the Hall coefficient, in contrast to recent experimental findings. We propose a doping dependent scattering rate, possibly due to quenched short-range charge fluctuations below optimal doping, to consistently describe both the Hall data and the longitudinal conductivities.
Coherent quantum transport in hybrid Nb-InGaAs-Nb Josephson junctions
Delfanazari, Kaveh; Puddy, R.; Ma, P.; Cao, M.; Yi, T.; Gul, Y.; Farrer, I.; Ritchie, D.; Joyce, H.; Kelly, M.; Smith, C.
Because of the recently reported detection of Majorana fermions states at the superconductor-semiconductor (S-Sm) interface in InAs nanowire devices, the study of hybrid structures has received renewed interest. In this paper we present experimental results on proximity induced superconductivity in a high-mobility two-dimensional electron gas in InGaAs heterostructures. Eight symmetric S-Sm-S Josephson junctions were fabricated on a single InGaAs chip and each junction was measured individually using a lock-in measurement technique. The superconducting electrodes were made of Niobium (Nb). The measurements were carried out in a dilution fridge with a base temperature of 40 mK, and the quantum transport of junctions were measured below 800 mK. Owing to Andreev reflections at the S-Sm interfaces, the differential resistance (dV/dI) versus V curve shows the well-known subharmonic energy gap structure (SGS) at V = 2ΔNb/ne. The SGS features suppressed significantly with increasing temperature and magnetic field, leading to a shift of the SGSs toward zero bias. Our result paves the way for development of highly transparent hybrid S-Sm-S junctions and coherent circuits for quantum devices capable of performing quantum logic and processing functions.
Paredes-Gutiérrez, H.; Pérez-Merchancano, S. T.; Beltran-Rios, C. L.
2017-12-01
In this work, we study the quantum electron transport through a Quantum Dots Structure (QDs), with different geometries, embedded in a Quantum Well (QW). The behaviour of the current through the nanostructure (dot and well) is studied considering the orbital spin coupling of the electrons and the Rashba effect, by means of the second quantization theory and the standard model of Green’s functions. Our results show the behaviour of the current in the quantum system as a function of the electric field, presenting resonant states for specific values of both the external field and the spin polarization. Similarly, the behaviour of the current on the nanostructure changes when the geometry of the QD and the size of the same are modified as a function of the polarization of the electron spin and the potential of quantum confinement.
Wigner Transport Simulation of Resonant Tunneling Diodes with Auxiliary Quantum Wells
Lee, Joon-Ho; Shin, Mincheol; Byun, Seok-Joo; Kim, Wangki
2018-03-01
Resonant-tunneling diodes (RTDs) with auxiliary quantum wells ( e.g., emitter prewell, subwell, and collector postwell) are studied using a Wigner transport equation (WTE) discretized by a thirdorder upwind differential scheme. A flat-band potential profile is used for the WTE simulation. Our calculations revealed functions of the auxiliary wells as follows: The prewell increases the current density ( J) and the peak voltage ( V p ) while decreasing the peak-to-valley current ratio (PVCR), and the postwell decreases J while increasing the PVCR. The subwell affects J and PVCR, but its main effect is to decrease V p . When multiple auxiliary wells are used, each auxiliary well contributes independently to the transport without producing side effects.
Anomalous transport phenomena in CeCoIn{sub 5} close to quantum critical point
Energy Technology Data Exchange (ETDEWEB)
Onari, S. [Department of Applied Physics, Nagoya University, Nagoya 464-8603 (Japan)]. E-mail: onari@fcs.coe.nagoya-u.ac.jp; Kontani, H. [Department of Physics, Nagoya University, Nagoya 464-8602 (Japan); Tanaka, Y. [Department of Applied Physics, Nagoya University, Nagoya 464-8603 (Japan)
2007-03-15
Various transport coefficients show striking deviations from conventional Fermi-liquid behaviors in many electron systems which are close to antiferromagnetic (AF) quantum critical points (QCP). For example, Hall coefficients and Nernst coefficients in three-dimensional heavy fermion CeCoIn{sub 5} and CeCu{sub 6-x}Au{sub x} increase remarkably at low temperatures. These temperature dependences are too strong to explain in terms of the relaxation time approximation. To elucidate the origin of these anomalous transport phenomena in three-dimensional systems, we study the role of current vertex corrections (CVC) based on the fluctuation exchange (FLEX) approximation. We find that the Hall coefficient and the Nernst coefficient strongly increase due to the CVC in the vicinity of the AF QCP, even in three-dimensional systems.
Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices
Energy Technology Data Exchange (ETDEWEB)
Gramich, J., E-mail: joerg.gramich@unibas.ch; Baumgartner, A.; Schönenberger, C. [Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel (Switzerland)
2016-04-25
We report thermally activated transport resonances for biases below the superconducting energy gap in a carbon nanotube quantum dot (QD) device with a superconducting Pb and a normal metal contact. These resonances are due to the superconductor's finite quasi-particle population at elevated temperatures and can only be observed when the QD life-time broadening is considerably smaller than the gap. This condition is fulfilled in our QD devices with optimized Pd/Pb/In multi-layer contacts, which result in reproducibly large and “clean” superconducting transport gaps with a strong conductance suppression for subgap biases. We show that these gaps close monotonically with increasing magnetic field and temperature. The accurate description of the subgap resonances by a simple resonant tunneling model illustrates the ideal characteristics of the reported Pb contacts and gives an alternative access to the tunnel coupling strengths in a QD.
Fang, Jingtian
As transistors, the most basic component of central processing units (CPU) in all electronic products, are scaling down to the nanometer scale, quantum mechanical effects must be studied to investigate their performance. A formalism to treat quantum electronic transport at the nanometer scale based on empirical pseudopotentials is presented in this dissertation. We develop the transport equations and show the expressions to calculate the device characteristics, such as device current and charge density. We apply this formalism to study ballistic transport in a gate-all-around (GAA) silicon nanowire field-effect transistor (FET) with a body-size of 0.39 nm, a gate length of 6.52 nm, and an effective oxide thickness of 0.43 nm. Simulation results show that this device exhibits a subthreshold slope (SS) of ˜66 mV/decade and a drain-induced barrier-lowering of ~2.5 mV/V. This formalism is also applied to assess the ballistic performance of FETs with armchair-edge graphene nanoribbon (aGNRs) and silicon nanowire (SiNWs) channels and with gate lengths ranging from 5 nm to 15 nm. The device characteristics of the transistors with a 5 nm gate length are compared. Source-to-drain tunneling effects are investigated for SiNWFETs and GNRFETs by comparing the I-V characteristics of each respective transistor with different channel lengths. While a uniform dielectric constant is assumed in solving Poisson equation for the devices simulated above, the knowledge of the atomistic (i.e., local) dielectric permittivity that considers the atomistic electron distribution and quantum-confinement effect is necessary to treat the electrostatic properties accurately. The local permittivity can also provide information about the dielectric property at the interfaces. We use the random-phase approximation, first-order perturbation theory, and empirical pseudopotentials to calculate the static polarizability, susceptibility, and dielectric response function in graphene and GNRs. While the
Acoustically induced spin transport in (110)GaAs quantum wells
Energy Technology Data Exchange (ETDEWEB)
Couto, Odilon D.D. Jr.
2008-09-29
In this work, we employ surface acoustic waves (SAWs) to transport and manipulate optically generated spin ensembles in (110) GaAs quantum wells (QWs). The strong carrier confinement into the SAW piezoelectric potential allows for the transport of spin-polarized carrier packets along well-defined channels with the propagation velocity of the acoustic wave. In this way, spin transport over distances exceeding 60 m is achieved, corresponding to spin lifetimes longer than 20 ns. The demonstration of such extremely long spin lifetimes is enabled by three main factors: (i) Suppression of the D'yakonov-Perel' spin relaxation mechanism for z-oriented spins in (110) IIIV QWs; (ii) Suppression of the Bir-Aronov-Pikus spin relaxation mechanism caused by the type-II SAW piezoelectric potential; (iii) Suppression of spin relaxation induced by the mesoscopic carrier confinement into narrow stripes along the SAW wave front direction. A spin transport anisotropy under external magnetic fields (B{sub ext}) is demonstrated for the first time. Employing the well-defined average carrier momentum impinged by the SAW, we analyze the spin dephasing dynamics during transport along the [001] and [1 anti 10] in-plane directions. For transport along [001], fluctuations of the internal magnetic field (B{sub int}), which arises from the spin-orbit interaction associated with the bulk inversion asymmetry of the crystal, lead to decoherence within 2 ns as the spins precess around B{sub ext}. In contrast, for transport along the [1 anti 10] direction, the z-component of the spin polarization is maintained for times one order of magnitude longer due to the non-zero average value of B{sub int}. The dephasing anisotropy between the two directions is fully understood in terms of the dependence of the spin-orbit coupling on carrier momentum direction, as predicted by the D'yakonov-Perel' mechanism for the (110) system. (orig.)
Ab initio quantum-enhanced optical phase estimation using real-time feedback control
DEFF Research Database (Denmark)
Berni, Adriano; Gehring, Tobias; Nielsen, Bo Melholt
2015-01-01
as demonstrated in a variety of different optical systems(3-8). Most of these accounts, however, deal with the measurement of a very small shift of an already known phase, which is in stark contrast to ab initio phase estimation where the initial phase is unknown(9-12). Here, we report on the realization......Optical phase estimation is a vital measurement strategy that is used to perform accurate measurements of various physical quantities including length, velocity and displacements(1,2). The precision of such measurements can be greatly enhanced by the use of entangled or squeezed states of light...... of a quantum-enhanced and fully deterministic ab initio phase estimation protocol based on real-time feedback control. Using robust squeezed states of light combined with a real-time Bayesian adaptive estimation algorithm, we demonstrate deterministic phase estimation with a precision beyond the quantum shot...
Tunable spin-polarized edge transport in inverted quantum-well junctions
Nanclares, Dimy; Lima, Leandro R. F.; Lewenkopf, Caio H.; da Silva, Luis G. G. V. Dias
2017-10-01
Inverted HgTe/CdTe quantum wells have been used as a platform for the realization of two-dimensional topological insulators, bulk insulator materials with spin-helical metallic edge states protected by time-reversal symmetry. This paper investigates the spectrum and the charge transport in HgTe/CdTe quantum well junctions both in the topological regime and in the absence of time-reversal symmetry. We model the system using the Bernevig-Hughes-Zhang effective Hamiltonian and compute the transport properties using recursive Green's functions with a finite differences' method. Specifically, we have studied the material's spatially resolved conductance in a setup with a gated central region, forming monopolar (n -n'-n ) and heteropolar (n -p -n , n -TI-n ) double junctions, which have been recently realized in experiments. We find regimes in which the edge states carry spin-polarized currents in the central region even in the presence of a small magnetic field, which breaks time-reversal symmetry. More interestingly, the conductance displays spin-dependent, Fabry-Perót-like oscillations as a function of the central gate voltage producing tunable, fully spin-polarized currents through the device.
DEFF Research Database (Denmark)
Skovgård, Troels Suhr; Gregersen, Niels; Lorke, Michael
2011-01-01
The modulation bandwidth for a quantum dot light-emitting device is calculated using a detailed model for the spontaneous emission including the optical and electronic density-of-states. We show that the Purcell enhancement of the spontaneous emission rate depends critically on the degree...... of inhomogeneous broadening relative to the cavity linewidth and can improve the modulation speed only within certain parameter regimes....
Gómez-Silva, G.; Orellana, P. A.; Anda, E. V.
2018-02-01
In the present work, we investigate the thermoelectric properties of a T-shaped double quantum dot system coupled to two metallic leads incorporating the intra-dot Coulomb interaction. We explore the role of the interference effects and Coulomb blockade on the thermoelectric efficiency of the system in the linear and nonlinear regimes. We studied as well the effect of a Van-Hove singularity of the leads density of states (DOS) at the neighborhood of the Fermi energy, a situation that can be obtained using a carbon nanotube, a graphene nano-ribbon or other contacts with one-dimensional properties. The system is studied above the Kondo temperature. The Coulomb blockade of the electronic charges is studied using the Hubbard III approximation, which properly describes the transport properties of this regime. In the linear response, our results show an enhancement of the thermopower and the figure of merit of the system. For a nonlinear situation, we calculate the thermoelectric efficiency and power output, concluding that the T-shaped double quantum dot is an efficient thermoelectric device. Moreover, we demonstrate the great importance of the DOS Van-Hove singularity at the neighborhood of the Fermi energy to obtain a very significant increase in the thermoelectric efficiency of the system.
Observation of quantum-limited spin transport in strongly interacting two-dimensional Fermi gases
Olsen, Ben A.; Luciuk, Chris; Smale, Scott; Böttcher, Florian; Sharum, Haille; Trotzky, Stefan; Enss, Tilman; Thywissen, Joseph H.
2017-04-01
Conjectured quantum bounds on transport appear to be respected in many strongly interacting many-body systems. Since transport occurs as a system relaxes to equilibrium, many such bounds can be recast as an upper bound on the local relaxation rate kB T / ℏ . Systems saturating this ``Planckian'' bound lack well defined quasiparticles promoting transport. We measure the transport properties of 2D ultracold Fermi gases of 40K during transverse demagnetization in a magnetic field gradient. Using a phase-coherent spin-echo sequence, we distinguish bare spin diffusion from the Leggett-Rice effect, in which demagnetization is slowed by the precession of spin current around the local magnetization. When the 2D scattering length is tuned near an s-wave Feshbach resonance to be comparable to the inverse Fermi wave vector kF- 1 , we find that the bare transverse spin diffusivity reaches a minimum of 1 . 7(6) ℏ / m . Demagnetization is also reflected in the growth rate of the s-wave contact, observed using time-resolved rf spectroscopy. At unitarity, the contact rises to 0 . 28(3) kF2 per particle, measuring the breaking of scaling symmetry. Our observations support the conjecture that under strong scattering, the local relaxation rate is bounded from above by kB T / ℏ .
Effects of Oscillatory Deformations on the Coherent and Incoherent Quantum Transport
Behzadi, Naghi; Ahansaz, Bahram
2017-11-01
Inspired by the works of Caruso (New J. Phys. 16, 055015 (2014) and Scholak et al. (J. Phys. B: At. Mol. Opt. Phys. 44, 184012 2011), which state that for a large class of complex noisy networks, the optimal efficiency of quantum transport is universally obtained by mixing coherent (Hamiltonian) and incoherent (noisy) parts where the contribution of the coherent part is strictly more than the incoherent one, we examine the effect of oscillatory deformations on two simple prototypes in order to study their effects on the efficiency of coherent and incoherent energy transport. The prototypes are interchangeable to each other only by a simple phase modulation, such that the dynamics for the first type is only coherent, while for the second one the coherent evolution is completely suppressed and the evolution of the system is only incoherent (noisy). In this regard, it is shown that there exist a special deformation by which the efficiency of incoherent transport becomes better than the coherent one. This result suggests that in the noisy networks with collective harmonic motions, the optimality of transport can be occurred in such a way that the contribution of incoherent term is more than the coherent one.
Gong, Jia-Min; Tang, Qi; Sun, Yu-Hang; Qiao, Lin
2015-03-01
We studied the trace distance, the Hellinger distance, and the Bures distance geometric quantum discords (GQDs) for a two-spin Heisenberg XX chain with the Dzyaloshinsky-Moriya (DM) interaction and the external magnetic fields. We found that considerable enhancement of the GQDs can be achieved by introducing the DM interaction, and their maxima were obtained when the strength of the DM interaction approaches infinity. The external magnetic fields and the increase of the temperature can also enhance the GQDs to some extent during certain specific parameter regions.
Enhancing Physician Empathy: Optimizing Learner Potential for Narrative Transportation
Directory of Open Access Journals (Sweden)
Casey Hester
2016-12-01
Full Text Available This article argues for the pedagogical usefulness of engaging with literary texts in the formal training of physicians and healthcare workers. It suggests that particular “skills” in reading and engaging with narrative are as readily teachable to healthcare students as are skills in reading x-rays or in diagnosing symptoms. It focuses on three phenomena associated with literary (and other forms of narrative – namely, the recognition of characters, vicarious experience, and the experience of fellow feeling – and relates them to three categories in cognitive psychology: Theory of Mind, Narrative Transportation, and Empathy. It presents a survey of empirical studies in cognitive psychology that demonstrates the effectiveness of literary narrative in producing these psychological states, and ends by demonstrating how the teaching of a literary narrative – Bastard Out of Carolina – has enhanced these states in students planning on a career in medicine. Such enhancement, the article suggests, are produced by literary features such as imagery, defamiliarization, and patterned organization on the levels of phonology, semantics, and story structure.
Graphene frameworks promoted electron transport in quantum dot-sensitized solar cells.
Zhu, Yanyan; Meng, Xin; Cui, Huijuan; Jia, Suping; Dong, Jianhui; Zheng, Jianfeng; Zhao, Jianghong; Wang, Zhijian; Li, Li; Zhang, Li; Zhu, Zhenping
2014-08-27
Graphene frameworks (GFs) were incorporated into TiO2 photoanode as electron transport medium to improve the photovoltaic performance of quantum dot-sensitized solar cells (QDSSCs) for their excellent conductivity and isotropic framework structure that could permit rapid charge transport. Intensity modulated photocurrent/photovoltage spectroscopy and electrochemical impedance spectroscopy results show that the electron transport time (τ(d)) of 1.5 wt % GFs/TiO2 electrode is one-fifth of that of the TiO2 electrode, and electron lifetime (τ(n)) and diffusion path length (Ln) are thrice those of the TiO2 electrode. Results also revealed that the GFs/TiO2 electrode has a shorter electron transport time (τ(d)), as well as longer electron lifetime (τ(n)) and diffusion path length (Ln), than conventional 2D graphene sheets/TiO2 electrode, thus indicating that GFs could promote rapid electron transfer in TiO2 photoanodes. Photocurrent-voltage curves demonstrated that when incorporating 1.5 wt % GFs into TiO2 photoanode, a maximum power conversion efficiency of 4.2% for QDSSCs could be achieved. This value was higher than that of TiO2 photoanode and 2D graphene sheets/TiO2 electrode. In addition, the reasons behind the sensitivity of photoelectric conversion efficiency to the graphene concentration in the TiO2 were also systematically investigated. Our results provide a basic understanding of how GFs can efficiently promote electron transport in TiO2-based solar cells.
Energy-scales convergence for optimal and robust quantum transport in photosynthetic complexes
Energy Technology Data Exchange (ETDEWEB)
Mohseni, M. [Google Research, Venice, California 90291 (United States); Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Shabani, A. [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); Department of Chemistry, University of California at Berkeley, Berkeley, California 94720 (United States); Lloyd, S. [Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Rabitz, H. [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States)
2014-01-21
Underlying physical principles for the high efficiency of excitation energy transfer in light-harvesting complexes are not fully understood. Notably, the degree of robustness of these systems for transporting energy is not known considering their realistic interactions with vibrational and radiative environments within the surrounding solvent and scaffold proteins. In this work, we employ an efficient technique to estimate energy transfer efficiency of such complex excitonic systems. We observe that the dynamics of the Fenna-Matthews-Olson (FMO) complex leads to optimal and robust energy transport due to a convergence of energy scales among all important internal and external parameters. In particular, we show that the FMO energy transfer efficiency is optimum and stable with respect to important parameters of environmental interactions including reorganization energy λ, bath frequency cutoff γ, temperature T, and bath spatial correlations. We identify the ratio of k{sub B}λT/ℏγg as a single key parameter governing quantum transport efficiency, where g is the average excitonic energy gap.
Computational study of the two-terminal transport of Floquet quantum Hall insulators
Yap, Han Hoe; Zhou, Longwen; Wang, Jian-Sheng; Gong, Jiangbin
2017-10-01
Periodic driving fields can induce topological phase transitions, resulting in Floquet topological phases with intriguing properties such as very large Chern numbers and unusual edge states. Whether such Floquet topological phases could generate robust edge state conductance much larger than their static counterparts is an interesting question. In this paper, working under the Keldysh formalism, we study two-lead transport via the edge states of irradiated quantum Hall insulators using the method of recursive Floquet-Green's functions. Focusing on a harmonically-driven Hofstadter model, we show that quantized Hall conductance as large as 8 e2/h can be realized but only after applying the so-called Floquet sum rule. To assess the robustness of edge state transport, we analyze the DC conductance, time-averaged current profile, and local density of states. It is found that copropagating chiral edge modes are more robust against disorder and defects as compared with the remarkable counterpropagating edge modes, as well as certain symmetry-restricted Floquet edge modes. Furthermore, we go beyond the wide-band limit, which is often assumed for the leads, to study how the conductance quantization (after applying the Floquet sum rule) of Floquet edge states can be affected if the leads have finite bandwidths. These results may be useful for the design of transport devices based on Floquet topological matter.
Foster, Samuel; Thesberg, Mischa; Neophytou, Neophytos
2017-11-01
Nanocomposites are promising candidates for the next generation of thermoelectric materials since they exhibit extremely low thermal conductivities as a result of phonon scattering on the boundaries of the various material phases. The nanoinclusions, however, should not degrade the thermoelectric power factor, and ideally should increase it, so that benefits to the ZT figure of merit can be achieved. In this work we employ the nonequilibrium Green's function quantum transport method to calculate the electronic and thermoelectric coefficients of materials embedded with nanoinclusions. For computational effectiveness we consider two-dimensional nanoribbon geometries, however, the method includes the details of geometry, electron-phonon interactions, quantization, tunneling, and the ballistic to diffusive nature of transport, all combined in a unified approach. This makes it a convenient and accurate way to understand electronic and thermoelectric transport in nanomaterials, beyond semiclassical approximations, and beyond approximations that deal with the complexities of the geometry. We show that the presence of nanoinclusions within a matrix material offers opportunities for only weak energy filtering, significantly lower in comparison to superlattices, and thus only moderate power factor improvements. However, we describe how such nanocomposites can be optimized to limit degradation in the thermoelectric power factor and elaborate on the conditions that achieve the aforementioned mild improvements. Importantly, we show that under certain conditions, the power factor is independent of the density of nanoinclusions, meaning that materials with large nanoinclusion densities which provide very low thermal conductivities can also retain large power factors and result in large ZT figures of merit.
Energy-scales convergence for optimal and robust quantum transport in photosynthetic complexes
International Nuclear Information System (INIS)
Mohseni, M.; Shabani, A.; Lloyd, S.; Rabitz, H.
2014-01-01
Underlying physical principles for the high efficiency of excitation energy transfer in light-harvesting complexes are not fully understood. Notably, the degree of robustness of these systems for transporting energy is not known considering their realistic interactions with vibrational and radiative environments within the surrounding solvent and scaffold proteins. In this work, we employ an efficient technique to estimate energy transfer efficiency of such complex excitonic systems. We observe that the dynamics of the Fenna-Matthews-Olson (FMO) complex leads to optimal and robust energy transport due to a convergence of energy scales among all important internal and external parameters. In particular, we show that the FMO energy transfer efficiency is optimum and stable with respect to important parameters of environmental interactions including reorganization energy λ, bath frequency cutoff γ, temperature T, and bath spatial correlations. We identify the ratio of k B λT/ℏγg as a single key parameter governing quantum transport efficiency, where g is the average excitonic energy gap
Plasmon polariton enhanced mid-infrared photodetectors based on Ge quantum dots in Si
Yakimov, A. I.; Kirienko, V. V.; Bloshkin, A. A.; Armbrister, V. A.; Dvurechenskii, A. V.
2017-10-01
Quantum dot based infrared (IR) photodetectors (QDIPs) have the potential to provide meaningful advances to the next generation of imaging systems due to their sensitivity to normal incidence radiation, large optical gain, low dark currents, and high operating temperature. SiGe-based QDIPs are of particular interest as they are compatible with silicon integration technology but suffer from the low absorption coefficient and hence small photoresponse in the mid-wavelength IR region. Here, we report on the plasmonic enhanced Ge/Si QDIPs with tailorable wavelength optical response and polarization selectivity. Ge/Si heterostructures with self-assembled Ge quantum dots are monolithically integrated with periodic two-dimensional arrays of subwavelength holes (2DHAs) perforated in gold films to convert the incident electromagnetic IR radiation into the surface plasmon polariton (SPP) waves. The resonant responsivity of the plasmonic detector at a wavelength of 5.4 μm shows an enhancement of up to thirty times over a narrow spectral bandwidth (FWHM = 0.3 μm), demonstrating the potentiality of this approach for the realization of high-performance Ge/Si QDIPs that require high spectral resolution. The possibility of the polarization-sensitive detection in Ge/Si QDIPs enhanced with a stretched-lattice 2DHA is reported. The excitation of SPP modes and the near-field components are investigated with the three-dimensional finite-element frequency-domain method. The role that plasmonic electric field plays in QDIP enhancement is discussed.
Zharkikh, Y S; Tretyak, O V
2003-01-01
The electron scattering mechanisms in the dimensionally quantized channels of silicon MOS-structures are investigated. The conclusion of the Coulomb scattering mechanism prevailing is made from the ratio of transport and quantum lifetimes. The experimental transport mobility values are compared with the Born approximation calculations. It is shown that the agreement of the experimental and calculated mobility's values can be obtained by taking into account the interference effect of remote ion potentials.
Transport phenomena in correlated quantum liquids: Ultracold Fermi gases and F/N junctions
Li, Hua
Landau Fermi-liquid theory was first introduced by L. D. Landau in the effort of understanding the normal state of Fermi systems, where the application of the concept of elementary excitations to the Fermi systems has proved very fruitful in clarifying the physics of strongly correlated quantum systems at low temperatures. In this thesis, I use Landau Fermi-liquid theory to study the transport phenomena of two different correlated quantum liquids: the strongly interacting ultracold Fermi gases and the ferromagnet/normal-metal (F/N) junctions. The detailed work is presented in chapter II and chapter III of this thesis, respectively. Chapter I holds the introductory part and the background knowledge of this thesis. In chapter II, I study the transport properties of a Fermi gas with strong attractive interactions close to the unitary limit. In particular, I compute the transport lifetimes of the Fermi gas due to superfluid fluctuations above the BCS transition temperature Tc. To calculate the transport lifetimes I need the scattering amplitudes. The scattering amplitudes are dominated by the superfluid fluctuations at temperatures just above Tc. The normal scattering amplitudes are calculated from the Landau parameters. These Landau parameters are obtained from the local version of the induced interaction model for computing Landau parameters. I also calculate the leading order finite temperature corrections to the various transport lifetimes. A calculation of the spin diffusion coefficient is presented in comparison to the experimental findings. Upon choosing a proper value of F0a, I am able to present a good match between the theoretical result and the experimental measurement, which indicates the presence of the superfluid fluctuations near Tc. Calculations of the viscosity, the viscosity/entropy ratio and the thermal conductivity are also shown in support of the appearance of the superfluid fluctuations. In chapter III, I study the spin transport in the low
International Nuclear Information System (INIS)
Park, Jong Hyeok; Lim, Yong Taik; Park, O Ok; Yu, Jae-Woong; Kim, Jai Kyeong; Kim, Young Chul
2004-01-01
Light-emitting devices based on environmentally stable, blue-emitting polymer/dielectric nanolayer nanocomposites were fabricated by blending poly(di-octylfluorene) (PDOF) with organo-clay. By reducing the excimer formation that leads to long wavelength tails, the photoluminescence (PL) and electroluminescence (EL) color purity of the device was enhanced. When a conjugated polymer/dielectric nanolayer nanocomposite is applied to an EL device, we expect an electronic structure similar to the well-known quantum well in small nanodomains. The ratio of PDOF/organo-clay was regulated from 2:1 to 0.5:1 (w/w). The light-emitting device of 0.5:1 (w/w) blend demonstrated the highest quantum efficiency (QE), 0.72% (ph/el), which is ∼500 times higher value compared with that of the pure PDOF layer device. However, the driving voltage of the nanocomposite devices tended to increase with increasing organo-clay content
Giant photocurrent enhancement by transition metal doping in quantum dot sensitized solar cells
Rimal, Gaurab; Pimachev, Artem K.; Yost, Andrew J.; Poudyal, Uma; Maloney, Scott; Wang, Wenyong; Chien, TeYu; Dahnovsky, Yuri; Tang, Jinke
2016-09-01
A huge enhancement in the incident photon-to-current efficiency of PbS quantum dot (QD) sensitized solar cells by manganese doping is observed. In the presence of Mn dopants with relatively small concentration (4 at. %), the photoelectric current increases by an average of 300% (up to 700%). This effect cannot be explained by the light absorption mechanism because both the experimental and theoretical absorption spectra demonstrate several times decreases in the absorption coefficient. To explain such dramatic increase in the photocurrent we propose the electron tunneling mechanism from the LUMO of the QD excited state to the Zn2SnO4 (ZTO) semiconductor photoanode. This change is due to the presence of the Mn instead of Pb atom at the QD/ZTO interface. The ab initio calculations confirm this mechanism. This work proposes an alternative route for a significant improvement of the efficiency for quantum dot sensitized solar cells.
Giant photocurrent enhancement by transition metal doping in quantum dot sensitized solar cells
Energy Technology Data Exchange (ETDEWEB)
Rimal, Gaurab; Pimachev, Artem K.; Yost, Andrew J.; Poudyal, Uma; Maloney, Scott; Wang, Wenyong; Chien, TeYu; Dahnovsky, Yuri, E-mail: yurid@uwyo.edu, E-mail: jtang2@uwyo.edu; Tang, Jinke, E-mail: yurid@uwyo.edu, E-mail: jtang2@uwyo.edu [Department of Physics and Astronomy, University of Wyoming, Laramie, Wyoming 82071 (United States)
2016-09-05
A huge enhancement in the incident photon-to-current efficiency of PbS quantum dot (QD) sensitized solar cells by manganese doping is observed. In the presence of Mn dopants with relatively small concentration (4 at. %), the photoelectric current increases by an average of 300% (up to 700%). This effect cannot be explained by the light absorption mechanism because both the experimental and theoretical absorption spectra demonstrate several times decreases in the absorption coefficient. To explain such dramatic increase in the photocurrent we propose the electron tunneling mechanism from the LUMO of the QD excited state to the Zn{sub 2}SnO{sub 4} (ZTO) semiconductor photoanode. This change is due to the presence of the Mn instead of Pb atom at the QD/ZTO interface. The ab initio calculations confirm this mechanism. This work proposes an alternative route for a significant improvement of the efficiency for quantum dot sensitized solar cells.
Energy Technology Data Exchange (ETDEWEB)
Nan, Feng; Shen, Mingrong; Fang, Liang, E-mail: zhkang@suda.edu.cn, E-mail: lfang@suda.edu.cn [College of Physics, Optoelectronics and Energy and Jiangsu Key Laboratory of Thin Films, Soochow University, Suzhou 215006 (China); Kang, Zhenhui, E-mail: zhkang@suda.edu.cn, E-mail: lfang@suda.edu.cn [Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-based Functional Materials and Devices, and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006 (China); Wang, Junling [School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 (Singapore)
2015-04-13
Carbon quantum dots (CQDs) coated BiVO{sub 4} inverse opal (io-BiVO{sub 4}) structure that shows dramatic improvement of photoelectrochemical hydrogen generation has been fabricated using electrodeposition with a template. The io-BiVO{sub 4} maximizes photon trapping through slow light effect, while maintaining adequate surface area for effective redox reactions. CQDs are then incorporated to the io-BiVO{sub 4} to further improve the photoconversion efficiency. Due to the strong visible light absorption property of CQDs and enhanced separation of the photoexcited electrons, the CQDs coated io-BiVO{sub 4} exhibit a maximum photo-to-hydrogen conversion efficiency of 0.35%, which is 6 times higher than that of the pure BiVO{sub 4} thin films. This work is a good example of designing composite photoelectrode by combining quantum dots and photonic crystal.
Enhanced quantum efficiency for CsI grown on a graphite-based substrate coating
Friese, J; Homolka, J; Kastenmüller, A; Maier-Komor, P; Peter, M; Zeitelhack, K; Kienle, P; Körner, H J
1999-01-01
Quantum efficiencies (QE) in the vacuum ultraviolet (VUV) wavelength region have been measured for solid CsI layers on various substrates. The CsI films were deposited applying electron beam evaporation. The QE measurements were performed utilizing synchrotron radiation as well as light from a deuterium lamp. A GaAsP diode with a sensitivity calibration traceable to a primary radiation standard was used for normalization. For CsI layers grown on resin-stabilized graphite films a significant enhancement of QE was observed. Substrates suitable for gas detector applications and aging properties were investigated. The procedures to prepare and reproduce high quantum efficient CsI layers are described.
Green function study of quantum transport in ultra-small devices with embedded atomistic clusters
International Nuclear Information System (INIS)
Barker, J R; Martinez, A; Svizhenko, A; Anantram, A; Asenov, A
2006-01-01
Transport in limiting scale MOSFET transistors will be strongly influenced by quantum effects and the presence of atomistic scattering centres either intentionally or un-intentionally present in the channel and the device environs. The scattering in such systems is non-asymptotic and the selfaveraging conditions of the Kohn-Luttinger theorem fail so that a self-energy for impurity scattering does not exist. Atomistic scattering must therefore be treated non-perturbatively. Previously it has been shown that quantized micro-vortices may occur at definite energies in the current flow contributing to both the blocking effect and to effective mobility. The present study uses the Glasgow and NASA NEGF simulators to study vortex formation and tunnelling through small clusters of atomistic impurities arranged with various configurations within the 5 nm wide by 12 nm long channel of a Double Gate MOSFET. The I-V characteristics and the threshold voltage are severely affected by the distribution of the charges in the channel. A variety of different geometry atomistic clusters have been studied. Examination of the energy dependent current density allows an evaluation of the admixture of strong quantum flows such as micro-vortices to the net current. It is found that the threshold voltage and conductance are strongly dependent on the impurity configuration. The I-V characteristics are monotonic in most cases due to the strong thermal smoothing that prevents resolution of the mode structure
Proton transport in barium stannate: classical, semi-classical and quantum regimes.
Geneste, Grégory; Ottochian, Alistar; Hermet, Jessica; Dezanneau, Guilhem
2015-07-15
Density-functional theory calculations are performed to investigate proton transport in BaSnO3. Structural optimizations in the stable and saddle point configurations for transfer (hopping) and reorientation allow description of the high-temperature classical and semi-classical regimes, in which diffusion occurs by over-barrier motion. At lower temperature (typically below 300 K), we describe the thermally-assisted quantum regime, in which protonic motion is of quantum nature and occurs in "coincidence" configurations favored by thermal fluctuations of the surrounding atoms. Both the non-adiabatic and the adiabatic limits are examined. In the adiabatic limit, the protonic energy landscape in the coincidence configuration is very flat. Path-integral molecular dynamics simulations of the proton in the coincidence potential reveal, in the transfer case, that the density of probability of H(+) has its maximum at the saddle point, because the zero-point energy exceeds the coincidence barrier. Arguments are given that support the adiabatic picture for the transfer mechanism. In the case of reorientation, the time scales for the existence of the coincidence and for protonic motion, as estimated from the time-energy uncertainty principle by using a simple one-dimensional model, are of the same order of magnitude, suggesting that the adiabatic limit is not reached. Protonic transfer and reorientation in this oxide are therefore governed by different mechanisms below room temperature.
Multi-Valued Logic Gates based on Ballistic Transport in Quantum Point Contacts
Seo, M.; Hong, C.; Lee, S.-Y.; Choi, H. K.; Kim, N.; Chung, Y.; Umansky, V.; Mahalu, D.
2014-01-01
Multi-valued logic gates, which can handle quaternary numbers as inputs, are developed by exploiting the ballistic transport properties of quantum point contacts in series. The principle of a logic gate that finds the minimum of two quaternary number inputs is demonstrated. The device is scalable to allow multiple inputs, which makes it possible to find the minimum of multiple inputs in a single gate operation. Also, the principle of a half-adder for quaternary number inputs is demonstrated. First, an adder that adds up two quaternary numbers and outputs the sum of inputs is demonstrated. Second, a device to express the sum of the adder into two quaternary digits [Carry (first digit) and Sum (second digit)] is demonstrated. All the logic gates presented in this paper can in principle be extended to allow decimal number inputs with high quality QPCs.
Quantum transport in low-dimensional AlGaN/GaN systems
International Nuclear Information System (INIS)
Spirito, D.; Frucci, G.; Di Gaspare, A.; Di Gaspare, L.; Giovine, E.; Notargiacomo, A.; Roddaro, S.; Beltram, F.; Evangelisti, F.
2011-01-01
In this work, we investigated the magnetotransport properties of a two dimensional electron gas hosted in an AlGaN/AlN/GaN heterostructure and one-dimensional devices fabricated on it. At cryogenic temperature, high mobility and long mean free path is achieved, allowing ballistic transport experiments. Longitudinal resistivity measured in Hall bar geometry shows well-developed Shubnikov–de Haas oscillations with amplitude modulation. Amongst possible mechanisms, the zero-field spin splitting may be the origin of the observed effects. Split gate quantum point contacts were fabricated by electron beam lithography. Linear conductance measurements at zero magnetic field show clear quantized conductance plateaus at 2e 2 /h and 4e 2 /h. Non-perfectly quantized conductance values are found for higher plateaus, suggesting the presence of impurity scattering.
Energy Technology Data Exchange (ETDEWEB)
Wensorra, Jakob
2009-03-20
The goal of this work has been to investigate und understand the electronic transport properties of vertical GaAs/AlAs nanocolumn resonant tunneling diodes (RTDs) and field effect transistors (RTTs) as well as of vertical InAs nanocolumn phase interference diodes. Besides the fabrication and electrical characterization of the devices, numerical calculations, simulations and quantum transport models represent the second important part of the work. GaAs/AlAs and InAs nanocolumns with lateral dimensions down to 30 nm have been processed by top-down approach. Room temperature DC electrical measurements on the nano-RTDs show a distinct negative differential resistance in the I-V characteristics for devices down to 30 nm lateral dimension. The miniaturization of the RTDs leads to the degradation of the transport properties, especially of the peak to valley current ratio (PVR), due to the increased surface scattering. Apart from the main current peak, new substructures can be observed in the I-V characteristics. These are shoulder like features for columns with diameters between 80 nm and 100 nm but become clear peaks when the column diameters are in the 55-75 nm range. For sub-65 nm column lateral dimensions, a strong increase of the PVR and a sharp single peak is observed. A local maximum of the PVR of 3 is reached for columns with 50 nm diameter. The sub-40 nm devices show only space charge limited currents in the I-V characteristics. This behavior can be shifted to smaller or larger diameters by increasing or reduction of the channel doping. For the smallest nanocolumns the lateral quantum confinement, caused by the low dimensionality of the system, leads to the formation of a 3D quantum-point-contact (QPC) in front of the DBQW structure. The quantization in this QPC depends on the column diameter and for a 50 nm column it exceeds the room temperature thermal broadening of the Fermi distribution function of about 25 meV. The measurements of the nano-RTTs indicate a
Directory of Open Access Journals (Sweden)
Antipov A.
2015-01-01
Full Text Available The nanostructures with different morphology have been obtained by us by methods of both direct laser modification (from cw to fs laser radiation of the target surface/thin films and laser evaporation of the target substance in liquid to produce the colloid systems, and then – to deposite substance on substrate from colloid, and also – by a single drop deposition technique. The analysis of induced nanostructures has been carried out by absorption spectroscopy, scanning electron microscopy and transmission electron microscopy. The island conductivity is dominant for the nanocluster semiconductor systems induced by laser ablation technique, and electroresistance can dramatically decrease due to spontaneous selected multichannel/parallel electron transportation trajectories. A tunneling quantum coherent effect takes place for electron conductivity for the case.
Directory of Open Access Journals (Sweden)
A A Shokri
2013-10-01
Full Text Available In this paper, we have investigated the spin-dependent transport properties and electron entanglement in a mesoscopic system, which consists of two semi-infinite leads (as source and drain separated by a typical quantum wire with a given potential. The properties studied include current-voltage characteristic, electrical conductivity, Fano factor and shot noise, and concurrence. The calculations are based on the transfer matrix method within the effective mass approximation. Using the Landauer formalism and transmission coefficient, the dependence of the considered quantities on type of potential well, length and width of potential well, energy of transmitted electron, temperature and the voltage have been theoretically studied. Also, the effect of the above-mentioned factors has been investigated in the nanostructure. The application of the present results may be useful in designing spintronice devices.
Dynamics of energy transport and entropy production in ac-driven quantum electron systems
Ludovico, María Florencia; Moskalets, Michael; Sánchez, David; Arrachea, Liliana
2016-07-01
We analyze the time-resolved energy transport and the entropy production in ac-driven quantum coherent electron systems coupled to multiple reservoirs at finite temperature. At slow driving, we formulate the first and second laws of thermodynamics valid at each instant of time. We identify heat fluxes flowing through the different pieces of the device and emphasize the importance of the energy stored in the contact and central regions for the second law of thermodynamics to be instantaneously satisfied. In addition, we discuss conservative and dissipative contributions to the heat flux and to the entropy production as a function of time. We illustrate these ideas with a simple model corresponding to a driven level coupled to two reservoirs with different chemical potentials.
QmeQ 1.0: An open-source Python package for calculations of transport through quantum dot devices
DEFF Research Database (Denmark)
Kiršanskas, Gediminas; Pedersen, Jonas Nyvold; Karlström, Olov
2017-01-01
QmeQ is an open-source Python package for numerical modeling of transport through quantum dot devices with strong electron–electron interactions using various approximate master equation approaches. The package provides a framework for calculating stationary particle or energy currents driven...
To investigate the coupled effects of solution chemistry and vadose zone processes on the mobility of quantum dot (QD) nanoparticles, laboratory scale transport experiments were performed. The complex coupled effects of ionic strength, size of QD aggregates, surface tension, contact angle, infiltrat...
Enhanced quantum cutting luminescence by Au nanorods through improving radiative transition rate
Zheng, Biao; Lin, Lin; Feng, Zhuohong; Huang, Lili; Zhuang, Luoqing; Wang, Zhezhe; Zheng, Zhiqiang
2017-11-01
Quantum cutting (QC) phosphor β-NaYF4:Tb3+, Yb3+ nanoparticles (NPs) are decorated with Au nanorods (NRs). By tailoring Au NRs longitudinal plasmon resonance to match the emission wavelength of Yb3+ ion, plasmon-enhanced near-infrared (NIR) QC luminescence is achieved through improving Yb3+ ion's radiative transition rate. The decay curves of Yb3+ ion in β-NaYF4:Tb3+, Yb3+ NPs decorated with Au NRs further confirm the improvement of radiative transition rate. The influence of Au NRs concentration on QC luminescence is also investigated, and the results show that the optimal concentration of Au NRs is 0.12% with the maximum enhancement factor about 3. Our study may not only path the way to achieve simultaneous excitation and emission enhancement of QC luminescence, but also provide a potential application as QC layer to silicon-based solar cells.
Gold Doping of Silver Nanoclusters: A 26-Fold Enhancement in the Luminescence Quantum Yield
Soldan, Giada
2016-04-10
A high quantum yield (QY) of photoluminescence (PL) in nanomaterials is necessary for a wide range of applications. Unfortunately, the weak PL and moderate stability of atomically precise silver nanoclusters (NCs) suppress their utility. Herein, we accomplished a ≥26-fold PL QY enhancement of the Ag29(BDT)12(TPP)4 cluster (BDT: 1,3-benzenedithiol; TPP: triphenylphosphine) by doping with a discrete number of Au atoms, producing Ag29-xAux(BDT)12(TPP)4, x=1-5. The Au-doped clusters exhibit an enhanced stability and an intense red emission around 660nm. Single-crystal XRD, mass spectrometry, optical, and NMR spectroscopy shed light on the PL enhancement mechanism and the probable locations of the Au dopants within the cluster.
Directory of Open Access Journals (Sweden)
Andrea V. Bragas
2011-03-01
Full Text Available We report the enhancement of the optical second harmonic signal in non-centrosymmetric semiconductor CdS quantum dots, when they are placed in close contact with isolated silver nanoparticles. The intensity enhancement is about 1000. We also show that the enhancement increases when the incoming laser frequency $omega$ is tuned toward the spectral position of the silver plasmon at $2omega$, proving that the silver nanoparticle modifies the nonlinear emission.Received: 8 March 2011, Accepted: 30 May 2011; Edited by: L. Viña; Reviewed by: R. Gordon, Department of Electrical and Computer Engineering, University of Victoria, British Columbia, Canada; DOI: 10.4279/PIP.030002Cite as: P. M. Jais, C. von Bilderling, A. V. Bragas, Papers in Physics 3, 030002 (2011
Nanoimprint-Transfer-Patterned Solids Enhance Light Absorption in Colloidal Quantum Dot Solar Cells
Kim, Younghoon
2017-03-13
Colloidal quantum dot (CQD) materials are of interest in thin-film solar cells due to their size-tunable bandgap and low-cost solution-processing. However, CQD solar cells suffer from inefficient charge extraction over the film thicknesses required for complete absorption of solar light. Here we show a new strategy to enhance light absorption in CQD solar cells by nanostructuring the CQD film itself at the back interface. We use two-dimensional finite-difference time-domain (FDTD) simulations to study quantitatively the light absorption enhancement in nanostructured back interfaces in CQD solar cells. We implement this experimentally by demonstrating a nanoimprint-transfer-patterning (NTP) process for the fabrication of nanostructured CQD solids with highly ordered patterns. We show that this approach enables a boost in the power conversion efficiency in CQD solar cells primarily due to an increase in short-circuit current density as a result of enhanced absorption through light-trapping.
Surface-enhanced FAST CARS: en route to quantum nano-biophotonics
Voronine, Dmitri V.; Zhang, Zhenrong; Sokolov, Alexei V.; Scully, Marlan O.
2018-02-01
Quantum nano-biophotonics as the science of nanoscale light-matter interactions in biological systems requires developing new spectroscopic tools for addressing the challenges of detecting and disentangling weak congested optical signals. Nanoscale bio-imaging addresses the challenge of the detection of weak resonant signals from a few target biomolecules in the presence of the nonresonant background from many undesired molecules. In addition, the imaging must be performed rapidly to capture the dynamics of biological processes in living cells and tissues. Label-free non-invasive spectroscopic techniques are required to minimize the external perturbation effects on biological systems. Various approaches were developed to satisfy these requirements by increasing the selectivity and sensitivity of biomolecular detection. Coherent anti-Stokes Raman scattering (CARS) and surface-enhanced Raman scattering (SERS) spectroscopies provide many orders of magnitude enhancement of chemically specific Raman signals. Femtosecond adaptive spectroscopic techniques for CARS (FAST CARS) were developed to suppress the nonresonant background and optimize the efficiency of the coherent optical signals. This perspective focuses on the application of these techniques to nanoscale bio-imaging, discussing their advantages and limitations as well as the promising opportunities and challenges of the combined coherence and surface enhancements in surface-enhanced coherent anti-Stokes Raman scattering (SECARS) and tip-enhanced coherent anti-Stokes Raman scattering (TECARS) and the corresponding surface-enhanced FAST CARS techniques. Laser pulse shaping of near-field excitations plays an important role in achieving these goals and increasing the signal enhancement.
International Nuclear Information System (INIS)
Cheng Shuguang
2010-01-01
Recent experiments have confirmed that the electron-hole inhomogeneity in graphene is a new type of charge disorder. Motivated by such confirmation, we theoretically study the transport properties of a monolayer graphene (MLG) based p-n junction and a bilayer graphene (BLG) p-n junction in the quantum Hall regime where electron-hole puddles are considered. By using the non-equilibrium Green function method, both the current and conductance are obtained. We find that, in the presence of the electron-hole inhomogeneity, the lowest quantized conductance plateau at e 2 /h emerges in the MLG p-n junction under very small charge puddle disorder strength. For a BLG p-n junction, however, the conductance in the p-n region is enhanced with charge puddles, and the lowest quantized conductance plateau emerges at 2e 2 /h. Besides, when an ideal quantized conductance plateau is formed for a MLG p-n junction, the universal conductance fluctuation is found to be 2e 2 /3h. Furthermore, we also investigate the influence of Anderson disorder on such p-n junctions and the comparison and discussion are given accordingly. To compare the two models with different types of disorder, we investigate the conductance distribution specially. Finally the influence of disorder strength on the conductance of a MLG p-n junction is investigated.
Liu, Donghua; Chen, Xiaosong; Hu, Yibin; Sun, Tai; Song, Zhibo; Zheng, Yujie; Cao, Yongbin; Cai, Zhi; Cao, Min; Peng, Lan; Huang, Yuli; Du, Lei; Yang, Wuli; Chen, Gang; Wei, Dapeng; Wee, Andrew Thye Shen; Wei, Dacheng
2018-01-15
Graphene is regarded as a potential surface-enhanced Raman spectroscopy (SERS) substrate. However, the application of graphene quantum dots (GQDs) has had limited success due to material quality. Here, we develop a quasi-equilibrium plasma-enhanced chemical vapor deposition method to produce high-quality ultra-clean GQDs with sizes down to 2 nm directly on SiO 2 /Si, which are used as SERS substrates. The enhancement factor, which depends on the GQD size, is higher than conventional graphene sheets with sensitivity down to 1 × 10 -9 mol L -1 rhodamine. This is attributed to the high-quality GQDs with atomically clean surfaces and large number of edges, as well as the enhanced charge transfer between molecules and GQDs with appropriate diameters due to the existence of Van Hove singularities in the electronic density of states. This work demonstrates a sensitive SERS substrate, and is valuable for applications of GQDs in graphene-based photonics and optoelectronics.
Chiral Molecule-Enhanced Extinction Ratios of Quantum Dots Coupled to Random Plasmonic Structures.
Bezen, Lior; Yochelis, Shira; Jayarathna, Dilhara; Bhunia, Dinesh; Achim, Catalina; Paltiel, Yossi
2018-03-06
Devices based on self-assembled hybrid colloidal quantum dots (CQDs) coupled with specific organic linker molecules are a promising way to simply realize room-temperature, spectrally tunable light detectors. Nevertheless, this type of devices usually has low quantum efficiency. Plasmonics has been shown as an efficient tool in guiding and confining light at nanoscale dimensions. As plasmonic modes exhibit highly confined fields, they locally increase light-matter interactions and consequently enhance the performance of CQD-based photodetectors. Recent publications presented experimental results of large extinction enhancement from a monolayer of CQDs coupled to random gold nanoislands using a monolayer of organic alkyl linkers. We report here that a twofold larger extinction enhancement in the visible spectrum is observed when a monolayer of helical chiral molecules connects the CQDs to the gold structure instead of a monolayer of achiral linkers. We also show that this effect provides insight into the chirality of the molecules within the monolayer. In future work, we plan to evaluate the potential of these results to be used in the construction of a more efficient and sensitive photon detector based on surface QDs, as well as to supply a simple way to map the chirality of a single chiral monolayer.
Spectral dependence of the linewidth enhancement factor in quantum dot lasers
Energy Technology Data Exchange (ETDEWEB)
Zubov, F. I., E-mail: fedyazu@mail.ru [Russian Academy of Sciences, St. Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation); Shernyakov, Yu. M.; Maximov, M. V. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Zhukov, A. E. [Russian Academy of Sciences, St. Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation); Livshits, D. A. [Innolume GmbH (Germany); Payusov, A. S.; Nadtochiy, A. M. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Savelyev, A. V.; Kryzhanovskaya, N. V. [Russian Academy of Sciences, St. Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation); Gordeev, N. Yu. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)
2013-12-15
The spectral analysis of amplified spontaneous emission is used to determine the linewidth enhancement factor (α-factor) in lasers based on InAs/InGaAs quantum dots (QDs) in a wide spectral range near the ground-state optical transition energy. The effect of the pump current and number of QDs on the spectral dependences of the α-factor is examined. The temperature dependence of the spectra of the α-factor is experimentally determined for the first time for lasers with InAs/InGaAs QDs. An explanation is suggested for the observed anomalous decrease in the α-factor with increasing temperature.
Quantum and superquantum enhancements to two-sender, two-receiver channels
Quek, Yihui; Shor, Peter W.
2017-05-01
We study the consequences of superquantum nonlocal correlations as represented by the PR-box model of Popescu and Rohrlich, and show that PR boxes can enhance the capacity of noisy interference channels between two senders and two receivers. PR-box correlations violate Bell and CHSH inequalities and are thus stronger—more nonlocal—than quantum mechanics, yet weak enough to respect special relativity in prohibiting faster-than-light communication. Understanding their power will yield insight into the nonlocality of quantum mechanics. We exhibit two proof-of-concept channels: First, we show a channel between two sender-receiver pairs where the senders are not allowed to communicate, for which a shared superquantum bit (a PR box) allows perfect communication. This feat is not achievable with the best classical (senders share no resources) or quantum-entanglement-assisted (senders share entanglement) strategies. Second, we demonstrate a class of channels for which a tunable parameter ɛ achieves a double separation of capacities; for some range of ɛ , the superquantum-assisted strategy does better than the entanglement-assisted strategy, which in turn does better than the classical one.
The donor-supply electrode enhances performance in colloidal quantum dot solar cells
Maraghechi, Pouya
2013-07-23
Colloidal quantum dot (CQD) solar cells combine solution-processability with quantum-size-effect tunability for low-cost harvesting of the sun\\'s broad visible and infrared spectrum. The highest-performing colloidal quantum dot solar cells have, to date, relied on a depleted-heterojunction architecture in which an n-type transparent metal oxide such as TiO2 induces a depletion region in the p-type CQD solid. These devices have, until now, been limited by a modest depletion region depth produced in the CQD solid owing to limitations in the doping available in TiO2. Herein we report a new device geometry - one based on a donor-supply electrode (DSE) - that leads to record-performing CQD photovoltaic devices. Only by employing this new charge-extracting approach do we deepen the depletion region in the CQD solid and thereby extract notably more photocarriers, the key element in achieving record photocurrent and device performance. With the use of optoelectronic modeling corroborated by experiment, we develop the guidelines for building a superior CQD solar cell based on the DSE concept. We confirm that using a shallow-work-function terminal electrode is essential to producing improved charge extraction and enhanced performance. © 2013 American Chemical Society.
Electronic transport in the quantum spin Hall state due to the presence of adatoms in graphene
Lima, Leandro; Lewenkopf, Caio
Heavy adatoms, even at low concentrations, are predicted to turn a graphene sheet into a topological insulator with substantial gap. The adatoms mediate the spin-orbit coupling that is fundamental to the quantum spin Hall effect. The adatoms act as local spin-orbit scatterer inducing hopping processes between distant carbon atoms giving origin to transverse spin currents. Although there are effective models that describe spectral properties of such systems with great detail, quantitative theoretical work for the transport counterpart is still lacking. We developed a multiprobe recursive Green's function technique with spin resolution to analyze the transport properties for large geometries. We use an effective tight-binding Hamiltonian to describe the problem of adatoms randomly placed at the center of the honeycomb hexagons, which is the case for most transition metals. Our choice of current and voltage probes is favorable to experiments since it filters the contribution of only one spin orientation, leading to a quantized spin Hall conductance of e2 / h . We also discuss the electronic propagation in the system by imaging the local density of states and the electronic current densities. The authors acknowledge the Brazilian agencies CNPq, CAPES, FAPERJ and INCT de Nanoestruturas de Carbono for financial support.
Heat transport through quantum Hall edge states: Tunneling versus capacitive coupling to reservoirs
Aita, Hugo; Arrachea, Liliana; Naón, Carlos; Fradkin, Eduardo
2013-08-01
We study the heat transport along an edge state of a two-dimensional electron gas in the quantum Hall regime, in contact to two reservoirs at different temperatures. We consider two exactly solvable models for the edge state coupled to the reservoirs. The first one corresponds to filling ν=1 and tunneling coupling to the reservoirs. The second one corresponds to integer or fractional filling of the sequence ν=1/m (with m odd), and capacitive coupling to the reservoirs. In both cases, we solve the problem by means of nonequilibrium Green function formalism. We show that heat propagates chirally along the edge in the two setups. We identify two temperature regimes, defined by Δ, the mean level spacing of the edge. At low temperatures, TΔ, finite-size effects become irrelevant, but the heat transport strongly depends on the strength of the edge-reservoir interactions, in both cases. The thermal conductance for tunneling coupling grows linearly with T, whereas for the capacitive case, it saturates to a value that depends on the coupling strengths and the filling factors of the edge and the contacts.
Guan, Zhuo; Tang, Xiang-Yu; Nishimura, Taku; Katou, Hidetaka; Liu, Hui-Yun; Qing, Jing
2018-02-01
Soil contamination by diesel has been often reported as a result of accidental spillage, leakage and inappropriate use. Surfactant-enhanced soil flushing is a common remediation technique for soils contaminated by hydrophobic organic chemicals. In this study, soil flushing with linear alkylbenzene sulfonates (LAS, an anionic surfactant) was conducted for intact columns (15cm in diameter and 12cm in length) of diesel-contaminated farmland purple soil aged for one year in the field. Dynamics of colloid concentration in column outflow during flushing, diesel removal rate and resulting soil macroporosity change by flushing were analyzed. Removal rate of n-alkanes (representing the diesel) varied with the depth of the topsoil in the range of 14%-96% while the n-alkanes present at low concentrations in the subsoil were completely removed by LAS-enhanced flushing. Much higher colloid concentrations and larger colloid sizes were observed during LAS flushing in column outflow compared to water flushing. The X-ray micro-computed tomography analysis of flushed and unflushed soil cores showed that the proportion of fine macropores (30-250μm in diameter) was reduced significantly by LAS flushing treatment. This phenomenon can be attributed to enhanced clogging of fine macropores by colloids which exhibited higher concentration due to better dispersion by LAS. It can be inferred from this study that the application of LAS-enhanced flushing technique in the purple soil region should be cautious regarding the possibility of rapid colloid-associated contaminant transport via preferential pathways in the subsurface and the clogging of water-conducting soil pores. Copyright © 2017. Published by Elsevier B.V.
Ma, Jie; Guo, Huaming; Lei, Mei; Li, Yongtao; Weng, Liping; Chen, Yali; Ma, Yuling; Deng, Yingxuan; Feng, Xiaojuan; Xiu, Wei
2018-04-15
Both humic acid and colloid particle size effectively regulate colloid transport. However, little is known about effect of particle size and configuration of humic acid colloid (HA colloid ) on enhanced-transport of ferrihydrite colloid (FH colloid ) in porous media. Co-transport of HA colloid and FH colloid at different pH was systematically investigated by monitoring breakthrough curves (BTCs) in saturated sand columns. The colloid transport model and the (X)DLVO theory were used to reveal the mechanism of HA colloid -enhanced FH colloid transport in the columns. Results showed that HA colloid enhanced FH colloid transport in neutral and alkaline conditions. In neutral conditions, small HA colloid (F-HA colloid ) with chain-shaped structure enhanced FH colloid transport more prominently than pristine granular HA colloid . The chain-shaped F-HA colloid caused osmotic repulsion and elastic-steric repulsion between colloids and sand, leading to enhanced transport. However, the granular HA colloid readily occurred as deposition due to attachment and straining, which decreased the enhanced transport of FH colloid . In alkaline conditions, both HA colloid and F-HA colloid were chain-shaped, with longer chains of HA colloid than F-HA colloid . Ferrihydrite colloid transport was enhanced by HA colloid more significantly than F-HA colloid due to stronger repulsion between mixed HA colloid -FH colloid and sand. It suggested that regulation of particle size and morphology of HA colloid would enhance FH colloid transport and further help in understanding FH colloid -facilitated contaminants transport in porous media. Copyright © 2017 Elsevier B.V. All rights reserved.
Enhanced heat transport in environmental systems using microencapsulated phase change materials
Colvin, D. P.; Mulligan, J. C.; Bryant, Y. G.
1992-01-01
A methodology for enhanced heat transport and storage that uses a new two-component fluid mixture consisting of a microencapsulated phase change material (microPCM) for enhanced latent heat transport is outlined. SBIR investigations for NASA, USAF, SDIO, and NSF since 1983 have demonstrated the ability of the two-component microPCM coolants to provide enhancements in heat transport up to 40 times over that of the carrier fluid alone, enhancements of 50 to 100 percent in the heat transfer coefficient, practically isothermal operation when the coolant flow is circulated in an optimal manner, and significant reductions in pump work.
Spin magneto-transport in a Rashba-Dresselhaus quantum channel with single and double finger gates
Tang, Chi-Shung; Keng, Jia-An; Abdullah, Nzar Rauf; Gudmundsson, Vidar
2017-05-01
We address spin-resolved electronic transport properties in a Rashba-Dresselhaus quantum channel in the presence of an in-plane magnetic field. The strong Rashba-Dresselhaus effect induces an asymmetric spin-splitting energy spectrum with a spin-orbit-Zeeman gap. This asymmetric fact in energy spectrum may result in various quantum dynamic features in conductance due to the presence of finger gates. This asymmetric spin-splitting energy spectrum results in a bound state in continuum for electrons within ultralow energy regime with binding energies in order of 10-1 meV.
Energy Technology Data Exchange (ETDEWEB)
Wu, Hua; Zhang, Yu, E-mail: yuzhang@jlu.edu.cn; Lu, Min; Liu, Wenyan [Jilin University, State Key Laboratory on Integrated Optoelectronics and College of Electronic Science and Engineering (China); Xu, Jian [The Pennsylvania State University, Department of Engineering Science and Mechanics (United States); Yu, William W., E-mail: wyu6000@gmail.com [Jilin University, State Key Laboratory on Integrated Optoelectronics and College of Electronic Science and Engineering (China)
2016-07-15
With tunable emission wavelength, high photoluminescence quantum yield, and broad absorption, colloidal quantum dots are attractive for the application in optical fiber as dopants. However, most of the quantum dots have a large overlap between their absorption and photoluminescence spectra, resulting in reabsorption loss which hinders the realization of long-distance waveguides. Therefore, ZnCuInS/ZnSe/ZnS quantum dots with large Stokes shift were proposed to fabricate a liquid-core optical fiber in this work. In this work, ZnCuInS/ZnSe/ZnS QDs with an average size of 3.3 nm were synthesized and the optical properties of the QD-filled fiber were also investigated as a function of fiber length and doping concentration. Compared to the control sample filled with CdSe/CdS/ZnS quantum dots, the ZnCuInS/ZnSe/ZnS quantum dot-based waveguides showed reduced reabsorption and enhanced signal propagation, which demonstrates great potential of large Stokes-shift quantum dots in optical waveguide devices.Graphical AbstractA reduced reabsorption and enhanced propagation of ZnCuInS/ZnSe/ZnS QDs-doped liquid-core optical fiber was achieved due to the large Stokes shift.
International Nuclear Information System (INIS)
Luo Jian; Lu Di; Du Chaoling; Liu Youwen; Shi Daning; Lai Wei; Guo Chunlei; Gong Shangqing
2012-01-01
We theoretically investigate how to control the Rabi oscillation of excitons of the coupling quantum dots by manipulating static electric fields. Our results show that, for a single-photon process, when direct excitons change into indirect excitons with a bias applied on the sample, the Rabi oscillation rarely alters. However, for the two-photon process, a pronounced enhancement of Rabi oscillation is observed, which can be utilized as the logic gate in quantum information. (paper)
Reshak, A H
2017-09-20
The amalgamation of a wide optical band gap photocatalyst with visible-light-active CdO quantum dots (QDs) as sensitizers is one of the most efficient ways to improve photocatalytic performance under visible light irradiation. The photocatalytic performance of cadmium benzoate ((Cd(C 7 H 5 O 2 ) 2 ) 3 (CH 3 CN) 1 ) is comprehensively investigated. The estimated optical band gap of cadmium benzoate is 2.64 eV and the EPc and EPv are about -0.09 V (vs. NHE) and +2.55 V (vs. NHE), respectively, which implies that cadmium benzoate possesses a high negative reduction potential of excited electrons due to its higher conduction band position, and hence, the locations of the conduction band minimum and the valence band maximum meet the redox capacity. Thus, this composite photocatalyst exhibits superior activity in visible-light-driven photocatalytic H 2 evolution. We found that introducing the QDs enhance the photocatalytic performance towards the visible light region. The electronic band structure shows high k-dispersion bands around the Fermi level, which implies low effective masses, and hence, the high mobility carriers favor the enhancement of the charge transfer process. The mobility of the photogenerated carriers significantly influences the photocatalytic efficiency and the higher photogenerated carriers' mobility enhances the photocatalytic performance. Moreover, the result shows a great effective mass difference between electrons (e - ) and holes (h + ), which can facilitate the e - and h + migration and separation, and finally improve the photocatalytic performance. The large mobility difference is useful for the separation of e - and h + , the reduction of the e - and h + recombination rate, and the improvement of the photocatalytic activity. Thus, cadmium benzoate exhibits rapid generation of e - -h + pairs with photoexcitation and a high negative reduction potential of excited electrons due to its higher CB position. Based on these results one can conclude
Enhanced photoluminescence of corrugated Al2O3 film assisted by colloidal CdSe quantum dots.
Bai, Zhongchen; Hao, Licai; Zhang, Zhengping; Huang, Zhaoling; Qin, Shuijie
2017-05-19
We present the enhanced photoluminescence (PL) of a corrugated Al 2 O 3 film enabled by colloidal CdSe quantum dots. The colloidal CdSe quantum dots are fabricated directly on a corrugated Al 2 O 3 substrate using an electrochemical deposition (ECD) method in a microfluidic system. The photoluminescence is excited by using a 150 nm diameter ultraviolet laser spot of a scanning near-field optical microscope. Owing to the electron transfer from the conduction band of the CdSe quantum dots to that of Al 2 O 3 , the enhanced photoluminescence effect is observed, which results from the increase in the recombination rate of electrons and holes on the Al 2 O 3 surface and the reduction in the fluorescence of the CdSe quantum dots. A periodically-fluctuating fluorescent spectrum was exhibited because of the periodical wire-like corrugated Al 2 O 3 surface serving as an optical grating. The spectral topographic map around the fluorescence peak from the Al 2 O 3 areas covered with CdSe quantum dots was unique and attributed to the uniform deposition of CdSe QDs on the corrugated Al 2 O 3 surface. We believe that the microfluidic ECD system and the surface enhanced fluorescence method described in this paper have potential applications in forming uniform optoelectronic films of colloidal quantum dots with controllable QD spacing and in boosting the fluorescent efficiency of weak PL devices.
International Nuclear Information System (INIS)
Mishra, Utkarsh; Rakshit, Debraj; Prabhu, R; Sen, Aditi; Sen, Ujjwal
2016-01-01
Disordered systems form one of the centrestages of research in many body sciences and lead to a plethora of interesting phenomena and applications. A paradigmatic disordered system consists of a one-dimensional array of quantum spin-1/2 particles, governed by the Heisenberg spin glass Hamiltonian with natural or engineered quenched disordered couplings in an external magnetic field. These systems allow disorder-induced enhancement for bipartite and multipartite observables. Here we show that simultaneous application of independent quenched disorders results in disorder-induced enhancement, while the same is absent with individual application of the same disorders. We term the phenomenon as constructive interference and the corresponding parameter stretches as the Venus regions. Interestingly, it has only been observed for multiparty entanglement and is absent for the single- and two-party physical quantities. (paper)
Tsai, Meng-Lin
2015-12-16
By employing graphene quantum dots (GQDs), we have achieved a high efficiency of 16.55% in n-type Si heterojunction solar cells. The efficiency enhancement is based on the photon downconversion phenomenon of GQDs to make more photons absorbed in the depletion region for effective carrier separation, leading to the enhanced photovoltaic effect. The short circuit current and the fill factor are increased from 35.31 to 37.47 mA/cm2 and 70.29% to 72.51%, respectively. The work demonstrated here holds the promise for incorporating graphene-based materials in commercially available solar devices for developing ultra-high efficiency photovoltaic cells in the future.
Tsai, Meng-Lin; Tu, Wei-Chen; Tang, Libin; Wei, Tzu-Chiao; Wei, Wan-Rou; Lau, Shu Ping; Chen, Lih-Juann; He, Jr-Hau
2016-01-13
By employing graphene quantum dots (GQDs), we have achieved a high efficiency of 16.55% in n-type Si heterojunction solar cells. The efficiency enhancement is based on the photon downconversion phenomenon of GQDs to make more photons absorbed in the depletion region for effective carrier separation, leading to the enhanced photovoltaic effect. The short circuit current and the fill factor are increased from 35.31 to 37.47 mA/cm(2) and 70.29% to 72.51%, respectively. The work demonstrated here holds the promise for incorporating graphene-based materials in commercially available solar devices for developing ultrahigh efficiency photovoltaic cells in the future.
Enhancement of squeezing in resonance fluorescence of a driven quantum dot close to a graphene sheet
Fang, Wei; Wu, Qing-lin; Wu, Shao-ping; Li, Gao-xiang
2016-05-01
We investigate squeezing of the resonance fluorescence of a laser-driven quantum dot (QD) close to a graphene sheet. The coupling between the QD and the surface plasmon around the graphene sheet is frequency dependent in the terahertz region, which can be adjusted by the laser intensity. Distinct decay rates in different transition channels of dressed QDs can be achieved due to the tailored photon reservoir, which can be used to improve the squeezing. It is found that increases in both the dephasing rate and the environmental temperature are harmful to the squeezing. Meanwhile, an enhancement in the QD-plasmon coupling strength may reduce the fragility of squeezing against the decoherence process. Additionally, in the strong light-matter coupling region, squeezing can be largely enhanced by tuning the strength of the pump field and its detuning from the QD.
Zhao, Haiguang; Benetti, Daniele; Jin, Lei; Zhou, Yufeng; Rosei, Federico; Vomiero, Alberto
2016-10-01
Luminescent solar concentrators (LSCs) can potentially reduce the cost of solar cells by decreasing the photoactive area of the device and boosting the photoconversion efficiency (PCE). This study demonstrates the application of "giant" CdSe/Cd x Pb 1- x S core/shell quantum dots (QDs) as light harvesters in high performance LSCs with over 1.15% PCE. Pb addition is critical to maximize PCE. First, this study synthesizes "giant" CdSe/Cd x Pb 1- x S QDs with high quantum yield (40%), narrow size distribution (<10%), and stable photoluminescence in a wide temperature range (100-300 K). Subsequently these thick alloyed-shell QDs are embedded in a polymer matrix, resulting in a highly transparent composite with absorption spectrum covering the range 300-600 nm, and are applied as active material for prototype LSCs. The latter exhibits a 15% enhancement in efficiency with respect to 1% PCE of the pure-CdS-shelled QDs. This study attributes this increase to the contribution of Pb doping. The results demonstrate a straightforward approach to enhance light absorption in "giant" QDs by metal doping, indicating a promising route to broaden the absorption spectrum and increase the efficiency of LSCs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Directory of Open Access Journals (Sweden)
A. Malasi
2016-10-01
Full Text Available Plasmonic nanoparticles are amongst the most effective ways to resonantly couple optical energy into and out of nanometer sized volumes. However, controlling and/or tuning the transfer of this incident energy to the surrounding near and far field is one of the most interesting challenges in this area. Due to the dielectric properties of metallic silver (Ag, its nanoparticles have amongst the highest radiative quantum efficiencies (η, i.e., the ability to radiatively transfer the incident energy to the surrounding. Here we report the discovery that bimetallic nanoparticles of Ag made with immiscible and plasmonically weak Co metal can show comparable and/or even higher η values. The enhancement is a result of the narrowing of the plasmon bandwidth from these bimetal systems. The phenomenological explanation of this effect based on the dipolar approximation points to the reduction in radiative losses within the Ag nanoparticles when in contact with cobalt. This is also supported by a model of coupling between poor and good conductors based on the surface to volume ratio. This study presents a new type of bandwidth engineering, one based on using bimetal nanostructures, to tune and/or enhance the quality factor and quantum efficiency for near and far-field plasmonic applications.
Unusual interlayer quantum transport behavior caused by the zeroth Landau level in YbMnBi2.
Liu, J Y; Hu, J; Graf, D; Zou, T; Zhu, M; Shi, Y; Che, S; Radmanesh, S M A; Lau, C N; Spinu, L; Cao, H B; Ke, X; Mao, Z Q
2017-09-21
Relativistic fermions in topological quantum materials are characterized by linear energy-momentum dispersion near band crossing points. Under magnetic fields, relativistic fermions acquire Berry phase of π in cyclotron motion, leading to a zeroth Landau level (LL) at the crossing point, a signature unique to relativistic fermions. Here we report the unusual interlayer quantum transport behavior resulting from the zeroth LL mode observed in the time reversal symmetry breaking type II Weyl semimetal YbMnBi 2 . The interlayer magnetoresistivity and Hall conductivity of this material are found to exhibit surprising angular dependences under high fields, which can be well fitted by a model, which considers the interlayer quantum tunneling transport of the zeroth LL's Weyl fermions. Our results shed light on the unusual role of zeroth LLl mode in transport.The transport behavior of the carriers residing in the lowest Landau level is hard to observe in most topological materials. Here, Liu et al. report a surprising angular dependence of the interlayer magnetoresistivity and Hall conductivity arising from the lowest Landau level under high magnetic field in type II Weyl semimetal YbMnBi 2 .
Collet, P; Métens, S; Neishtadt, A; Zaslavsky, G; Chaotic Dynamics and Transport in Classical and Quantum Systems
2005-01-01
This book offers a modern updated review on the most important activities in today dynamical systems and statistical mechanics by some of the best experts in the domain. It gives a contemporary and pedagogical view on theories of classical and quantum chaos and complexity in hamiltonian and ergodic systems and their applications to anomalous transport in fluids, plasmas, oceans and atom-optic devices and to control of chaotic transport. The book is issued from lecture notes of the International Summer School on "Chaotic Dynamics and Transport in Classical and Quantum Systems" held in Cargèse (Corsica) 18th to the 30th August 2003. It reflects the spirit of the School to provide lectures at the post-doctoral level on basic concepts and tools. The first part concerns ergodicity and mixing, complexity and entropy functions, SRB measures, fractal dimensions and bifurcations in hamiltonian systems. Then, models of dynamical evolutions of transport processes in classical and quantum systems have been largely expla...
Quantum statistical description of transport of the quasi-particles in optic fibers
International Nuclear Information System (INIS)
Rasulova, M.Yu.; Hassan, T.; Mohamed Ridza bin Wahiddin; Umarov, B.
2006-12-01
On the basis of BBGKY hierarchy of quantum kinetic equations the quasi-quantum analogue of the linearized wave equation for one, two quasi-particles in optic fiber is obtained. The method which enables to obtain the quasi-quantum analogue of wave equations for any number of quasi- particles in fiber is suggested. (author)
Li, K. Y.; Shan, Q. S.; Zhu, R. P.; Yin, H.; Lin, Y. Y.; Wang, L. Q.
2015-04-01
The study on the quantum dot quantum well (QDQW) microstructure modified by choosing different ligands containing a sulfhydryl group is of significance because it enables one to regulate photoexcited free charge carriers' (FCCs') transport behaviours in high-quality CdTe/ligand QDs via a self-assembled way. The photoelectron characteristics of ligand-capped CdTe nanoparticles were probed by a combination of surface photovoltaic (SPV) and photoacoustic technologies, supplemented by a computer simulation method of the CASTEP module. The experiment reveals that the D-value ΔEWi obtained by the associated two parameters of the SPV spectroscopy was closely related to the quantum confinement energy in the self-assembled CdTe/CdS/ligand core-shell system. In the paper the D-value was termed the depth of QWs, which were buried in the space charge regions located in the graded-band-gap and on either side of the shell-CdS. Obvious resonance quantum tunnelling may occur in the energy band structure with deep QWs on using certain ligands, resulting in an extended diffusion length of the FCCs on illumination of the photon energy hν >= Eg, core-CdTe, and in a strong SPV response at a specific wavelength region. In addition, the carrier-longitudinal optical phonon interaction is the reciprocal of the carriers' lifetime. The d-frontier orbital in the graded-band-gap plays an important role in both the microstructure and the resonance quantum tunnelling of the QDQW system according to the CASTEP calculations.The study on the quantum dot quantum well (QDQW) microstructure modified by choosing different ligands containing a sulfhydryl group is of significance because it enables one to regulate photoexcited free charge carriers' (FCCs') transport behaviours in high-quality CdTe/ligand QDs via a self-assembled way. The photoelectron characteristics of ligand-capped CdTe nanoparticles were probed by a combination of surface photovoltaic (SPV) and photoacoustic technologies
78 FR 59880 - Enhanced Consumer Protections for Charter Air Transportation
2013-09-30
... sale of air transportation related to air ambulance services. Finally, the NPRM would make clear and... a ticket agent to hold out or sell air transportation on one carrier when the service will be... today is, under applicable law, a ``ticket agent.'' A ticket agent is defined in 49 U.S.C. 40102(a)(45...
International Nuclear Information System (INIS)
Appel, H.
2007-05-01
In part I of this work we present a double-pole approximation (DPA) to the response equations of time-dependent density functional theory (TDDFT). The double-pole approximation provides an exact description of systems with two strongly coupled excitations which are isolated from the rest of the spectrum. In contrast to the traditional single-pole approximation of TDDFT the DPA also yields corrections to the Kohn-Sham oscillator strengths. We also demonstrate how to invert the double-pole solution which allows us to predict matrix elements of the exchange-correlation kernel f xc from experimental input. We attempt some first steps towards a time-dependent generalization of reduced density matrix functional theory (RDMFT). In part II we derive equations of motion for natural orbitals and occupation numbers. Using the equation of motion for the occupation numbers we show that an adiabatic extension of presently known ground-state functionals of static RDMFT always leads to occupation numbers which are constant in time. From the stationary conditions of the equations of motion for the N-body correlations (correlated parts of the N-body matrices) we derive a new class of ground-state functionals which can be used in static RDMFT. Applications are presented for a one-dimensional model system where the time-dependent many-body Schroedinger equation can be propagated numerically. We use optimal control theory to find optimized laser pulses for transitions in a model for atomic Helium. From the numerically exact correlated wavefunction we extract the exact time evolution of natural orbitals and occupation numbers for (i) laser-driven Helium and (ii) electron-ion scattering. Part III of this work considers time-dependent quantum transport within TDDFT. We present an algorithm for the calculation of extended eigenstates of single-particle Hamiltonians which is especially tailored to a finite-difference discretization of the Schroedinger equation. We consider the propagation
Energy Technology Data Exchange (ETDEWEB)
Appel, H.
2007-05-15
In part I of this work we present a double-pole approximation (DPA) to the response equations of time-dependent density functional theory (TDDFT). The double-pole approximation provides an exact description of systems with two strongly coupled excitations which are isolated from the rest of the spectrum. In contrast to the traditional single-pole approximation of TDDFT the DPA also yields corrections to the Kohn-Sham oscillator strengths. We also demonstrate how to invert the double-pole solution which allows us to predict matrix elements of the exchange-correlation kernel f{sub xc} from experimental input. We attempt some first steps towards a time-dependent generalization of reduced density matrix functional theory (RDMFT). In part II we derive equations of motion for natural orbitals and occupation numbers. Using the equation of motion for the occupation numbers we show that an adiabatic extension of presently known ground-state functionals of static RDMFT always leads to occupation numbers which are constant in time. From the stationary conditions of the equations of motion for the N-body correlations (correlated parts of the N-body matrices) we derive a new class of ground-state functionals which can be used in static RDMFT. Applications are presented for a one-dimensional model system where the time-dependent many-body Schroedinger equation can be propagated numerically. We use optimal control theory to find optimized laser pulses for transitions in a model for atomic Helium. From the numerically exact correlated wavefunction we extract the exact time evolution of natural orbitals and occupation numbers for (i) laser-driven Helium and (ii) electron-ion scattering. Part III of this work considers time-dependent quantum transport within TDDFT. We present an algorithm for the calculation of extended eigenstates of single-particle Hamiltonians which is especially tailored to a finite-difference discretization of the Schroedinger equation. We consider the
International Nuclear Information System (INIS)
Sadeghi, S M
2009-01-01
We study the inhibition of optical excitation and enhancement of Rabi flopping and frequency in semiconductor quantum dots via plasmonic effects. This is done by demonstrating that the interaction of a quantum dot with a laser field in the vicinity of a metallic nanoparticle can be described in terms of optical Bloch equations with a plasmically normalized Rabi frequency. We show that in the weak-field regime plasmonic effects can suppress the interband transitions, inhibiting exciton generation. In the strong-field regime these effects delay the response of the quantum dot to the laser field and enhance Rabi flopping. We relate these to the conversion of Rabi frequency from a real quantity into a complex and strongly frequency-dependent quantity as plasmonic effects become significant. We show that, within the strong-field regime, in the wavelength range where real and imaginary parts of this frequency reach their maxima, a strongly frequency-dependent enhancement of carrier excitation can happen.
Olivares-Amaya, Roberto
The understanding of molecular effects in nanoscale environments is becoming increasingly relevant for various emerging fields. These include spectroscopy for molecular identification as well as in finding molecules for energy harvesting. Theoretical quantum chemistry has been increasingly useful to address these phenomena to yield an understanding of these effects. In the first part of this dissertation, we study the chemical effect of surface-enhanced Raman scattering (SERS). We use quantum chemistry simulations to study the metal-molecule interactions present in these systems. We find that the excitations that provide a chemical enhancement contain a mixed contribution from the metal and the molecule. Moreover, using atomistic studies we propose an additional source of enhancement, where a transition metal dopant surface could provide an additional enhancement. We also develop methods to study the electrostatic effects of molecules in metallic environments. We study the importance of image-charge effects, as well as field-bias to molecules interacting with perfect conductors. The atomistic modeling and the electrostatic approximation enable us to study the effects of the metal interacting with the molecule in a complementary fashion, which provides a better understanding of the complex effects present in SERS. In the second part of this dissertation, we present the Harvard Clean Energy Project, a high-throughput approach for a large-scale computational screening and design of organic photovoltaic materials. We create molecular libraries to search for candidates structures and use quantum chemistry, machine learning and cheminformatics methods to characterize these systems and find structure-property relations. The scale of this study requires an equally large computational resource. We rely on distributed volunteer computing to obtain these properties. In the third part of this dissertation we present our work related to the acceleration of electronic structure
Bessonov, Alexander A; Allen, Mark; Liu, Yinglin; Malik, Surama; Bottomley, Joseph; Rushton, Ashley; Medina-Salazar, Ivonne; Voutilainen, Martti; Kallioinen, Sami; Colli, Alan; Bower, Chris; Andrew, Piers; Ryhänen, Tapani
2017-06-27
Colloidal quantum dots (QDs) combined with a graphene charge transducer promise to provide a photoconducting platform with high quantum efficiency and large intrinsic gain, yet compatible with cost-efficient polymer substrates. The response time in these devices is limited, however, and fast switching is only possible by sacrificing the high sensitivity. Furthermore, tuning the QD size toward infrared absorption using conventional organic capping ligands progressively reduces the device performance characteristics. Here we demonstrate methods to couple large QDs (>6 nm in diameter) with organometal halide perovskites, enabling hybrid graphene phototransistor arrays on plastic foils that simultaneously exhibit a specific detectivity of 5 × 10 12 Jones and high video-frame-rate performance. PbI 2 and CH 3 NH 3 I co-mediated ligand exchange in PbS QDs improves surface passivation and facilitates electronic transport, yielding faster charge recovery, whereas PbS QDs embedded into a CH 3 NH 3 PbI 3 matrix produce spatially separated photocarriers leading to large gain.
International Nuclear Information System (INIS)
Dakhlaoui, H; Almansour, S
2016-01-01
In this work, the electronic properties of resonant tunneling diodes (RTDs) based on GaN-Al x Ga (1−x) N double barriers are investigated by using the non-equilibrium Green functions formalism (NEG). These materials each present a wide conduction band discontinuity and a strong internal piezoelectric field, which greatly affect the electronic transport properties. The electronic density, the transmission coefficient, and the current–voltage characteristics are computed with considering the spontaneous and piezoelectric polarizations. The influence of the quantum size on the transmission coefficient is analyzed by varying GaN quantum well thickness, Al x Ga (1−x) N width, and the aluminum concentration x Al . The results show that the transmission coefficient more strongly depends on the thickness of the quantum well than the barrier; it exhibits a series of resonant peaks and valleys as the quantum well width increases. In addition, it is found that the negative differential resistance (NDR) in the current–voltage ( I – V) characteristic strongly depends on aluminum concentration x Al . It is shown that the peak-to-valley ratio (PVR) increases with x Al value decreasing. These findings open the door for developing vertical transport nitrides-based ISB devices such as THz lasers and detectors. (paper)
H, Dakhlaoui; S, Almansour
2016-06-01
In this work, the electronic properties of resonant tunneling diodes (RTDs) based on GaN-Al x Ga(1-x)N double barriers are investigated by using the non-equilibrium Green functions formalism (NEG). These materials each present a wide conduction band discontinuity and a strong internal piezoelectric field, which greatly affect the electronic transport properties. The electronic density, the transmission coefficient, and the current-voltage characteristics are computed with considering the spontaneous and piezoelectric polarizations. The influence of the quantum size on the transmission coefficient is analyzed by varying GaN quantum well thickness, Al x Ga(1-x)N width, and the aluminum concentration x Al. The results show that the transmission coefficient more strongly depends on the thickness of the quantum well than the barrier; it exhibits a series of resonant peaks and valleys as the quantum well width increases. In addition, it is found that the negative differential resistance (NDR) in the current-voltage (I-V) characteristic strongly depends on aluminum concentration x Al. It is shown that the peak-to-valley ratio (PVR) increases with x Al value decreasing. These findings open the door for developing vertical transport nitrides-based ISB devices such as THz lasers and detectors. Project supported by the Deanship of Scientific Research of University of Dammam (Grant No. 2014137).
Strain induced effects on the transport properties of metamorphic InAlAs/InGaAs quantum wells
International Nuclear Information System (INIS)
Capotondi, F.; Biasiol, G.; Ercolani, D.; Grillo, V.; Carlino, E.; Romanato, F.; Sorba, L.
2005-01-01
The relationship between structural and low-temperature transport properties is explored for In x Al 1 - x As/In x Ga 1 - x As metamorphic quantum wells with x > 0.7 grown on GaAs by molecular beam epitaxy. Different step-graded buffer layers are used to gradually adapt the in-plane lattice parameter from the GaAs towards the InGaAs value. We show that using buffer layers with a suitable maximum In content the residual compressive strain in the quantum well region can be strongly reduced. Samples with virtually no residual strain in the quantum well region show a low-temperature electron mobility up to 29 m 2 /V s while for samples with higher residual compressive strain the low-temperature mobility is reduced. Furthermore, for samples with buffers inducing a tensile strain in the quantum well region, deep grooves are observed on the surface, and in correspondence we notice a strong deterioration of the low-temperature transport properties
Quantum dots as enhancers of the efficacy of bacterial lethal photosensitization
Narband, N.; Mubarak, M.; Ready, D.; Parkin, I. P.; Nair, S. P.; Green, M. A.; Beeby, A.; Wilson, M.
2008-11-01
Because of the increasing resistance of bacteria to antibiotics there is considerable interest in light-activated antimicrobial agents (LAAAs) as alternatives to antibiotics for treating localized infections. The purpose of this study was to determine whether CdSe/ZnS quantum dots (QD) could enhance the antibacterial activity of the LAAA, toluidine blue O (TBO). Suspensions of Staphylococcus aureus and Streptococcus pyogenes were exposed to white light (3600 lux) and TBO (absorbance maximum = 630 nm) in the presence and absence of 25 nm diameter QD (emission maximum = 627 nm). When the TBO:QD ratio was 2667:1, killing of Staph. aureus was enhanced by 1.72log10 units. In the case of Strep. pyogenes, an enhanced kill of 1.55log10 units was achieved using TBO and QD in the ratio 267:1. Singlet oxygen and fluorescence measurements showed that QD suppress the formation of singlet oxygen from TBO and that QD fluorescence is significantly quenched in the presence of TBO (70-90%). Enhanced killing appears to be attributable to a non-Förster resonance energy transfer mechanism, whereby the QD converts part of the incident light to the absorption maximum for TBO; hence more light energy is harvested, resulting in increased concentrations of bactericidal radicals. QD may, therefore, be useful in improving the efficacy of antimicrobial photodynamic therapy.
Quantum dots as enhancers of the efficacy of bacterial lethal photosensitization
International Nuclear Information System (INIS)
Narband, N; Parkin, I P; Mubarak, M; Nair, S P; Wilson, M; Ready, D; Green, M A; Beeby, A
2008-01-01
Because of the increasing resistance of bacteria to antibiotics there is considerable interest in light-activated antimicrobial agents (LAAAs) as alternatives to antibiotics for treating localized infections. The purpose of this study was to determine whether CdSe/ZnS quantum dots (QD) could enhance the antibacterial activity of the LAAA, toluidine blue O (TBO). Suspensions of Staphylococcus aureus and Streptococcus pyogenes were exposed to white light (3600 lux) and TBO (absorbance maximum = 630 nm) in the presence and absence of 25 nm diameter QD (emission maximum = 627 nm). When the TBO:QD ratio was 2667:1, killing of Staph. aureus was enhanced by 1.72log 10 units. In the case of Strep. pyogenes, an enhanced kill of 1.55log 10 units was achieved using TBO and QD in the ratio 267:1. Singlet oxygen and fluorescence measurements showed that QD suppress the formation of singlet oxygen from TBO and that QD fluorescence is significantly quenched in the presence of TBO (70-90%). Enhanced killing appears to be attributable to a non-Foerster resonance energy transfer mechanism, whereby the QD converts part of the incident light to the absorption maximum for TBO; hence more light energy is harvested, resulting in increased concentrations of bactericidal radicals. QD may, therefore, be useful in improving the efficacy of antimicrobial photodynamic therapy.
Theory of g-factor enhancement in narrow-gap quantum well heterostructures
Energy Technology Data Exchange (ETDEWEB)
Krishtopenko, S S; Gavrilenko, V I [Institute for Physics of Microstructures RAS, GSP-105, 603950, Nizhny Novgorod (Russian Federation); Goiran, M, E-mail: gavr@ipm.sci-nnov.ru, E-mail: michel.goiran@lncmi.cnrs.fr [Laboratoire National des Champs Magnetiques Intenses (LNCMI-T), CNRS UPR 3228 Universite de Toulouse, 143 Avenue de Rangueil, F-31400 Toulouse (France)
2011-09-28
We report on the study of the exchange enhancement of the g-factor in the two-dimensional (2D) electron gas in n-type narrow-gap semiconductor heterostructures. Our approach is based on the eight-band k{center_dot}p Hamiltonian and takes into account the band nonparabolicity, the lattice deformation, the spin-orbit coupling and the Landau level broadening in the {delta}-correlated random potential model. Using the 'screened' Hartree-Fock approximation we demonstrate that the exchange g-factor enhancement not only shows maxima at odd values of Landau level filling factors but, due to the conduction band nonparabolicity, persists at even filling factor values as well. The magnitude of the exchange enhancement, the amplitude and the shape of the g-factor oscillations are determined by both the screening of the electron-electron interaction and the Landau level width. The 'enhanced' g-factor values calculated for the 2D electron gas in InAs/AlSb quantum well heterostructures are compared with our earlier experimental data and with those obtained by Mendez et al (1993 Phys. Rev. B 47 13937) in magnetic fields up to 30 T. (paper)
Jimenez, Mawin J. M.; Oliveira, Rafael F.; Almeida, Tiago P.; Hensel Ferreira, Rafael C.; Bufon, Carlos Cesar B.; Rodrigues, Varlei; Pereira-da-Silva, Marcelo A.; Gobbi, Ângelo L.; Piazzetta, Maria H. O.; Riul, Antonio, Jr.
2017-12-01
Graphene is a breakthrough 2D material due to its unique mechanical, electrical, and thermal properties, with considerable responsiveness in real applications. However, the coverage of large areas with pristine graphene is a challenge and graphene derivatives have been alternatively exploited to produce hybrid and composite materials that allow for new developments, considering also the handling of large areas using distinct methodologies. For electronic applications there is significant interest in the investigation of the electrical properties of graphene derivatives and related composites to determine whether the characteristic 2D charge transport of pristine graphene is preserved. Here, we report a systematic study of the charge transport mechanisms of reduced graphene oxide chemically functionalized with sodium polystyrene sulfonate (PSS), named as GPSS. GPSS was produced either as quantum dots (QDs) or nanoplatelets (NPLs), being further nanostructured with poly(diallyldimethylammonium chloride) through the layer-by-layer (LbL) assembly to produce graphene nanocomposites with molecular level control. Current-voltage (I-V) measurements indicated a meticulous growth of the LbL nanostructures onto gold interdigitated electrodes (IDEs), with a space-charge-limited current dominated by a Mott-variable range hopping mechanism. A 2D intra-planar conduction within the GPSS nanostructure was observed, which resulted in effective charge carrier mobility (μ) of 4.7 cm2 V-1 s-1 for the QDs and 34.7 cm2 V-1 s-1 for the NPLs. The LbL assemblies together with the dimension of the materials (QDs or NPLs) were favorably used for the fine tuning and control of the charge carrier mobility inside the LbL nanostructures. Such 2D charge conduction mechanism and high μ values inside an interlocked multilayered assembly containing graphene-based nanocomposites are of great interest for organic devices and functionalization of interfaces.
International Nuclear Information System (INIS)
Jalilian-Marian, Jamal; Jeon, Sangyong; Venugopalan, Raju; Wirstam, Jens
2000-01-01
The one loop effective action in quantum field theory can be expressed as a quantum mechanical path integral over world lines, with internal symmetries represented by Grassmanian variables. In this paper, we develop a real time, many body, world line formalism for the one loop effective action. In particular, we study hot QCD and obtain the classical transport equations which, as Litim and Manuel have shown, reduce in the appropriate limit to the non-Abelian Boltzmann-Langevin equation first obtained by Boedeker. In the Vlasov limit, the classical kinetic equations are those that correspond to the hard thermal loop effective action. We also discuss the imaginary time world line formalism for a hot φ 4 theory, and elucidate its relation to classical transport theory. (c) 2000 The American Physical Society
International Nuclear Information System (INIS)
Di Ventra, Massimiliano; Pantelides, Sokrates T.
2000-01-01
The conventional Hellmann-Feynman theorem for the definition of forces on nuclei is not directly applicable to quantum time-dependent and transport problems. We present a rigorous derivation of a general Hellmann-Feynman-like theorem that applies to all quantum mechanical systems and reduces to well-known results for ground-state problems. It provides a rigorous definition of forces in time-dependent and transport problems. Explicit forms of Pulay-like forces are derived and the conditions for them to be zero are identified. A practical scheme for ab initio calculations of current-induced forces is described and the study of the transfer of a Si atom between two electrodes is presented as an example. (c) 2000 The American Physical Society
International Nuclear Information System (INIS)
Liu Zhang; Xu Weicheng; Fang Jianzhang; Xu Xiaoxin; Wu Shuxing; Zhu Ximiao; Chen Zehua
2012-01-01
Highlights: ► RGO/BiOI nanocomposites were synthesized by a reverse microemulsion method. ► Quantum sized BiOI nanoparticles can be obtained by this approach. ► Ascorbic acid was used as a reducing agent to reduce GO and seemed to be effective. ► RGO/BiOI presented outstanding visible-light-induced photocatalytic performance. ► Possible photocatalytic mechanism was proposed based on the experimental studies. - Abstract: Herein, a reverse microemulsion route was developed to synthesize bismuth oxyiodide (BiOI) nanocrystals and reduced graphene oxide (RGO) nanocomposites as a highly efficient photocatalyst, and both the formation of BiOI and the reduction of RGO were achieved in situ in microemulsions simultaneously at low temperature (60 °C). The uniform nanocrystal size and structure were indicated by XRD, TEM, and the reduction of GO by ascorbic acid was evidenced by FTIR, XPS, and Raman spectra techniques. The enhanced photoactivity of RGO/BiOI nanocomposites under visible light was attributed to improved light absorption and efficient charge separation and transportation.
Energy Technology Data Exchange (ETDEWEB)
Liu Zhang, E-mail: liuzhang0126@126.com [School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China); Xu Weicheng [School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China); Fang Jianzhang, E-mail: fangjzh@scnu.edu.cn [School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China); Xu Xiaoxin; Wu Shuxing; Zhu Ximiao; Chen Zehua [School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China)
2012-10-15
Highlights: Black-Right-Pointing-Pointer RGO/BiOI nanocomposites were synthesized by a reverse microemulsion method. Black-Right-Pointing-Pointer Quantum sized BiOI nanoparticles can be obtained by this approach. Black-Right-Pointing-Pointer Ascorbic acid was used as a reducing agent to reduce GO and seemed to be effective. Black-Right-Pointing-Pointer RGO/BiOI presented outstanding visible-light-induced photocatalytic performance. Black-Right-Pointing-Pointer Possible photocatalytic mechanism was proposed based on the experimental studies. - Abstract: Herein, a reverse microemulsion route was developed to synthesize bismuth oxyiodide (BiOI) nanocrystals and reduced graphene oxide (RGO) nanocomposites as a highly efficient photocatalyst, and both the formation of BiOI and the reduction of RGO were achieved in situ in microemulsions simultaneously at low temperature (60 Degree-Sign C). The uniform nanocrystal size and structure were indicated by XRD, TEM, and the reduction of GO by ascorbic acid was evidenced by FTIR, XPS, and Raman spectra techniques. The enhanced photoactivity of RGO/BiOI nanocomposites under visible light was attributed to improved light absorption and efficient charge separation and transportation.
North Dakota wheat transportation knowledge for market enhancement.
2010-07-01
North Dakota wheat producers are located long distances from major consumer and export markets. Understanding the competitive position of their products is important to focusing efforts for market development and transportation investments. Research ...
Tuning Spin- and Valley-Degeneracies in Multicomponent Quantum Well Transport
Prabhu-Gaunkar, Sunanda
The theme of this thesis is manipulation of spin and valley degeneracies in two-dimensional electron systems (2DES) by locally or globally controlling the energy gaps between the two spin states or multiple valley states. Degeneracies in 2DES can be controlled internally or externally with magnetic, strain, and electrostatic fields. With magneto-transport measurements we can probe these spin and valley energy gaps. Spin degeneracies in quantum wells (QW) can be controlled with magnetic field by changing the tilt angle of the field with respect to the sample. Valley degeneracies can be controlled principally by growing QWs of a certain orientation and width. Furthermore, the valley energies can be controlled externally by applying strain or electrostatic gated devices. We first consider transport signatures of controlled spin degeneracies. Magnetic fields can be used to control spin degeneracies and spin gaps by tuning the tilt angle of the field with respect to the sample plane. These spin dependencies can be observed at different tilt angles by conducting measurements of the longitudinal and Hall resistance. In particular, transport measurements in a Si/SiGe spin-split valley degenerate 2DES demonstrates anomalous rise of the transverse Hall resistance at certain quantized plateaus. With systematic tilted field data we map this anomaly to the longitudinal resistance, and also to directional derivatives of the longitudinal resistance. We also develop a theoretical model for estimating the spin-degenerate and spin-split density of states which we fit using the data on longitudinal resistance. We input the exactly calculated spin gaps at every tilt angle in the edge state model of quantum Hall effect, and we are able to provide a microscopic justification to the experimentally observed anomalous features by introducing a constant energy density of disordered states in our model. We next consider transport signatures of controlled valley degeneracies. Valley
Microwave-mediated heat transport in a quantum dot attached to leads
International Nuclear Information System (INIS)
Chi Feng; Dubi, Yonatan
2012-01-01
The thermoelectric effect in a quantum dot (QD) attached to two leads in the presence of microwave fields is studied by using the Keldysh nonequilibrium Green function technique. When the microwave is applied only on the QD and in the linear response regime, the main peaks in the thermoelectric figure of merit and the thermopower are found to decrease, with the emergence of a set of photon-induced peaks. Under this condition the microwave field cannot generate heat current or electrical bias voltage. Surprisingly, when the microwave field is applied only to one (bright) lead and not to the other (dark) lead or the QD, heat flows mostly from the dark to the bright lead, almost irrespective of the direction of the thermal gradient. We attribute this effect to microwave-induced opening of additional transport channels below the Fermi energy. The microwave field can change both the magnitude and the sign of the electrical bias voltage induced by the temperature gradient. (paper)
Quantum Transport and Non-Hermiticity on Flat-Band Lattices
Park, Hee Chul; Ryu, Jung-Wan; Myoung, Nojoon
2018-04-01
We investigate quantum transport in a flat-band lattice induced in a twisted cross-stitch lattice with Hermitian or non-Hermitian potentials, with a combination of parity and time-reversal symmetry invariant. In the given system, the transmission probability demonstrates a resonant behavior on the real part of the energy bands. Both of the potentials break the parity symmetry, which lifts the degeneracy of the flat and dispersive bands. In addition, non-Hermiticity conserving PT-symmetry induces a transition between the unbroken and broken PT-symmetric phases through exceptional points in momentum space. Characteristics of non-Hermitian and Hermitian bandgaps are distinguishable: The non-Hermitian bandgap is induced by separation toward complex energy, while the Hermitian bandgap is caused by the expelling of available states into real energy. Deviation of the two bandgaps follows as a function of the quartic power of the induced potential. It is notable that non-Hermiticity plays an important role in the mechanism of generating a bandgap distinguishable from a Hermitian bandgap.
International Nuclear Information System (INIS)
Weymann, I.; Barnas, J.
2006-01-01
The influence of intrinsic spin relaxation on spin-polarized cotunneling through quantum dots coupled to ferromagnetic leads is analyzed theoretically. It is shown that the zero bias anomaly, which occurs due to the interplay of single-barrier and double-barrier cotunneling processes, becomes suppressed by spin relaxation processes on the dot. Diode-like features of the transport characteristics in the cotunneling regime have been found in asymmetrical systems. These features are also suppressed by the spin relaxation processes
DEFF Research Database (Denmark)
Zelovich, Tamar; Hansen, Thorsten; Liu, Fulai
2017-01-01
A parameter-free version of the recently developed driven Liouville-von Neumann equation [T. Zelovich et al., J. Chem. Theory Comput. 10(8), 2927-2941 (2014)] for electronic transport calculations in molecular junctions is presented. The single driving rate, appearing as a fitting parameter in th......-box" algorithms to simulate electron dynamics in open quantum systems out of equilibrium.......A parameter-free version of the recently developed driven Liouville-von Neumann equation [T. Zelovich et al., J. Chem. Theory Comput. 10(8), 2927-2941 (2014)] for electronic transport calculations in molecular junctions is presented. The single driving rate, appearing as a fitting parameter...
QmeQ 1.0: An open-source Python package for calculations of transport through quantum dot devices
Kiršanskas, Gediminas; Pedersen, Jonas Nyvold; Karlström, Olov; Leijnse, Martin; Wacker, Andreas
2017-12-01
QmeQ is an open-source Python package for numerical modeling of transport through quantum dot devices with strong electron-electron interactions using various approximate master equation approaches. The package provides a framework for calculating stationary particle or energy currents driven by differences in chemical potentials or temperatures between the leads which are tunnel coupled to the quantum dots. The electronic structures of the quantum dots are described by their single-particle states and the Coulomb matrix elements between the states. When transport is treated perturbatively to lowest order in the tunneling couplings, the possible approaches are Pauli (classical), first-order Redfield, and first-order von Neumann master equations, and a particular form of the Lindblad equation. When all processes involving two-particle excitations in the leads are of interest, the second-order von Neumann approach can be applied. All these approaches are implemented in QmeQ. We here give an overview of the basic structure of the package, give examples of transport calculations, and outline the range of applicability of the different approximate approaches.
Wang, Yi-Yan; Xu, Sheng; Sun, Lin-Lin; Xia, Tian-Long
2018-02-01
Dirac semimetals, which host Dirac fermions and represent a new state of quantum matter, have been studied intensively in condensed-matter physics. The exploration of new materials with topological states is important in both physics and materials science. We report the synthesis and the transport properties of high-quality single crystals of YbMnSb2. YbMnSb2 is a new compound with metallic behavior. Quantum oscillations, including Shubnikov-de Haas (SdH) oscillation and de Haas-van Alphen-type oscillation, have been observed at low temperature and high magnetic field. Small effective masses and nontrivial Berry phase are extracted from the analyses of quantum oscillations, which provide the transport evidence for the possible existence of Dirac fermions in YbMnSb2. The measurements of angular-dependent interlayer magnetoresistance indicate that the interlayer transport is coherent. The Fermi surface of YbMnSb2 possesses a quasi-two-dimensional characteristic as determined by the angular dependence of SdH oscillation frequency. These findings suggest that YbMnSb2 is a new candidate of topological Dirac semimetals.
International Nuclear Information System (INIS)
Ncube, Siphephile; Chimowa, George; Chiguvare, Zivayi; Bhattacharyya, Somnath
2014-01-01
The superiority of the electronic transport properties of single-walled carbon nanotube (SWNT) ropes over SWNT mats is verified from low temperature and frequency-dependent transport. The overall change of resistance versus in nanotube mats shows that 3D variable range hopping is the dominant conduction mechanism within the 2–300 K range. The magneto-resistance (MR) is found to be predominantly negative with a parabolic nature, which can also be described by the hopping model. Although the positive upturn of the MR at low temperatures establishes the contribution from quantum interference, the inherent quantum transport in individual tubes is suppressed at elevated temperatures. Therefore, to minimize multi-channel effects from inter-tube interactions and other defects, two-terminal devices were fabricated from aligned SWNT (extracted from a mat) for low temperature transport as well as high-frequency measurements. In contrast to the mat, the aligned ropes exhibit step-like features in the differential conductance within the 80–300 K temperature range. The effects of plasmon propagation, unique to one dimension, were identified in electronic transport as a non-universal power-law dependence of the differential conductance on temperature and source-drain voltage. The complex impedance showed high power transmission capabilities up to 65 GHz as well as oscillations in the frequency range up to 30 GHz. The measurements suggest that aligned SWNT ropes have a realistic potential for high-speed device applications.
Novel quantum dot enhancement film with a super-wide color gamut for LCD displays
Ko, Yun-Hyuk; Park, Jea-Gun
2018-01-01
We present a novel quantum dot enhancement film (QDEF) with a remarkable RGB color gamut of over 100.4% (134.2%) of the Rec. 2020 standard (NTSC standard), respectively for a high-resolution liquid-crystal display (LCD). Our efficient QDEF was fabricated by using a highly transparent resin incorporated with high photoluminesce-quantum yield (PL-QY) and narrow full width at half maximum CsPbBr1I2 QDs (Pr-QDs) and CdSe/ZnS QDs (Cd-QDs). The proposed PrCd-QDEF in a LCD with color filters rendered a blue photoluminesce (PL) peak at 452 nm with a FWHM of 20.4 nm, a green PL peak at 530.1 nm with a FWHM of 23.8 nm, and a red color peak at 652.4 nm with a FWHM of 28.1 nm. Moreover, The PrCd-QDEF did not show any cross-talk between the RGB PL colors. Such promising optical results, along with the simple and cost-effective preparation technique, might encourage the manufacture of super high resolution LCDs using a PrCd-QDEF.
Janjua, Bilal
2014-04-01
We study the enhanced hole confinement by having a large bandgap AlGaN monolayer insertion (MLI) between the quantum well (QW) and the quantum barrier (QB). The numerical analysis examines the energy band alignment diagrams, using a self-consistent 6 × 6 k ·p method and, considering carrier distribution, recombination rates (Shockley-Reed-Hall, Auger, and radiative recombination rates), under equilibrium and forward bias conditions. The active region is based on AlaGa1-aN (barrier)/AlbGa1-bN (MLI)/AlcGa1-cN (well)/AldGa1-dN (barrier), where b > d > a > c. A large bandgap AlbGa1-bN mono layer, inserted between the QW and QB, was found to be effective in providing stronger hole confinement. With the proposed band engineering scheme, an increase of more than 30% in spatial overlap of carrier wavefunction was obtained, with a considerable increase in carrier density and direct radiative recombination rates. The single-QW-based UV-LED was designed to emit at 280 nm, which is an effective wavelength for water disinfection.
Toma, Andrea
2015-01-14
Terahertz spectroscopy has vast potentialities in sensing a broad range of elementary excitations (e.g., collective vibrations of molecules, phonons, excitons, etc.). However, the large wavelength associated with terahertz radiation (about 300 μm at 1 THz) severely hinders its interaction with nano-objects, such as nanoparticles, nanorods, nanotubes, and large molecules of biological relevance, practically limiting terahertz studies to macroscopic ensembles of these compounds, in the form of thick pellets of crystallized molecules or highly concentrated solutions of nanomaterials. Here we show that chains of terahertz dipole nanoantennas spaced by nanogaps of 20 nm allow retrieving the spectroscopic signature of a monolayer of cadmium selenide quantum dots, a significant portion of the signal arising from the dots located within the antenna nanocavities. A Fano-like interference between the fundamental antenna mode and the phonon resonance of the quantum dots is observed, accompanied by an absorption enhancement factor greater than one million. NETS can find immediate applications in terahertz spectroscopic studies of nanocrystals and molecules at extremely low concentrations. Furthermore, it shows a practicable route toward the characterization of individual nano-objects at these frequencies.
Toma, Andrea; Tuccio, Salvatore; Prato, Mirko; De Donato, Francesco; Perucchi, Andrea; Di Pietro, Paola; Marras, Sergio; Liberale, Carlo; Proietti Zaccaria, Remo; De Angelis, Francesco; Manna, Liberato; Lupi, Stefano; Di Fabrizio, Enzo; Razzari, Luca
2015-01-14
Terahertz spectroscopy has vast potentialities in sensing a broad range of elementary excitations (e.g., collective vibrations of molecules, phonons, excitons, etc.). However, the large wavelength associated with terahertz radiation (about 300 μm at 1 THz) severely hinders its interaction with nano-objects, such as nanoparticles, nanorods, nanotubes, and large molecules of biological relevance, practically limiting terahertz studies to macroscopic ensembles of these compounds, in the form of thick pellets of crystallized molecules or highly concentrated solutions of nanomaterials. Here we show that chains of terahertz dipole nanoantennas spaced by nanogaps of 20 nm allow retrieving the spectroscopic signature of a monolayer of cadmium selenide quantum dots, a significant portion of the signal arising from the dots located within the antenna nanocavities. A Fano-like interference between the fundamental antenna mode and the phonon resonance of the quantum dots is observed, accompanied by an absorption enhancement factor greater than one million. NETS can find immediate applications in terahertz spectroscopic studies of nanocrystals and molecules at extremely low concentrations. Furthermore, it shows a practicable route toward the characterization of individual nano-objects at these frequencies.
A fluid membrane enhances the velocity of cargo transport by small teams of kinesin-1
Li, Qiaochu; Tseng, Kuo-Fu; King, Stephen J.; Qiu, Weihong; Xu, Jing
2018-03-01
Kinesin-1 (hereafter referred to as kinesin) is a major microtubule-based motor protein for plus-end-directed intracellular transport in live cells. While the single-molecule functions of kinesin are well characterized, the physiologically relevant transport of membranous cargos by small teams of kinesins remains poorly understood. A key experimental challenge remains in the quantitative control of the number of motors driving transport. Here we utilized "motile fraction" to overcome this challenge and experimentally accessed transport by a single kinesin through the physiologically relevant transport by a small team of kinesins. We used a fluid lipid bilayer to model the cellular membrane in vitro and employed optical trapping to quantify the transport of membrane-enclosed cargos versus traditional membrane-free cargos under identical conditions. We found that coupling motors via a fluid membrane significantly enhances the velocity of cargo transport by small teams of kinesins. Importantly, enclosing a cargo in a fluid lipid membrane did not impact single-kinesin transport, indicating that membrane-dependent velocity enhancement for team-based transport arises from altered interactions between kinesins. Our study demonstrates that membrane-based coupling between motors is a key determinant of kinesin-based transport. Enhanced velocity may be critical for fast delivery of cargos in live cells.
Carrier transport in III–V quantum-dot structures for solar cells or photodetectors
International Nuclear Information System (INIS)
Wang Wenqi; Wang Lu; Jiang Yang; Ma Ziguang; Sun Ling; Liu Jie; Sun Qingling; Zhao Bin; Wang Wenxin; Liu Wuming; Jia Haiqiang; Chen Hong
2016-01-01
According to the well-established light-to-electricity conversion theory, resonant excited carriers in the quantum dots will relax to the ground states and cannot escape from the quantum dots to form photocurrent, which have been observed in quantum dots without a p–n junction at an external bias. Here, we experimentally observed more than 88% of the resonantly excited photo carriers escaping from InAs quantum dots embedded in a short-circuited p–n junction to form photocurrent. The phenomenon cannot be explained by thermionic emission, tunneling process, and intermediate-band theories. A new mechanism is suggested that the photo carriers escape directly from the quantum dots to form photocurrent rather than relax to the ground state of quantum dots induced by a p–n junction. The finding is important for understanding the low-dimensional semiconductor physics and applications in solar cells and photodiode detectors. (rapid communication)
Khan, Sarzamin; Lima, Alex A.; Larrudé, Dunieskys G.; Romani, Eric C.; Aucelio, Ricardo Q.
2014-04-01
A photoluminescent probe for the determination of captopril is proposed based on the enhancement of luminescence from 2-mercaptopropionic modified CdTe quantum dots (2-MPA-CdTe QDs). Under optimum conditions, the calibration model (the Langmuir binding isotherm) was linear up to 4.8 × 10-4 mol L-1 with equilibrium binding constant of 3.2 × 104 L mol-1 and limit of detection (xb + 3 sb) of 2.7 × 10-7 mol L-1 (59 ng mL-1). The approach was tested in the determination of captopril in pharmaceutical formulations and the results were in agreement with the ones obtained using reference method. The possible mechanism of interaction is also investigated by Raman and electronic absorption spectroscopy and dynamic light scattering.
Enhancement of the shot noise of a quantum dot–Luttinger lead system
International Nuclear Information System (INIS)
Yang, Kai-Hua; Liu, Bei-Yun; Wang, Huai-Yu; He, Xian
2013-01-01
We investigate the joint effects of the intralead electron interaction and Coulombic dot–lead interaction on the shot noise of a quantum dot coupled to Luttinger liquid leads. A formula of the shot noise is derived by applying the nonequilibrium Green function technique. The shot noise is enhanced by the dot–lead interaction. For a weak or moderately strong interaction the differential shot noise demonstrates resonant-like behavior as a function of bias and gate voltages. In the limit of strong interaction resonant behavior disappears and the differential shot noise and Fano factor scale as a power law in bias voltage. Under some parameters, the differential shot noise may become negative around resonant peaks, and the physical reason is analyzed.
Black phosphorus quantum dots/attapulgite nanocomposite with enhanced photocatalytic performance
Li, Xiazhang; Li, Feihong; Lu, Xiaowang; Zuo, Shixiang; Zhuang, Ziheng; Yao, Chao
Novel black phosphorus quantum dots/attapulgite (BPQDs/ATP) nanocomposites were prepared via a facile hydrothermal-deposition method. TEM showed that BPQDs dispersed evenly on the surface of ATP with uniform particle size about 5nm. UV-Vis revealed that the BPQDs/ATP composite showed wider visible light absorption range as compared with pure ATP. The photocatalytic activity was evaluated by degradation of bisphenol A (BPA). Results showed that BPQDs/ATP reached 90% degradation rate under solar light irradiation for 180min. The coherent heterostructure formed by BPQDs and ATP was responsible for the enhanced photocatalytic performance, due to the sensitization effect of BPQDs and the facilitation of charges separation.
Large g-factor enhancement in high-mobility InAs/AlSb quantum wells
International Nuclear Information System (INIS)
Sadofyev, Yu.G.; Ramamoorthy, A.; Naser, B.; Bird, J.P.; Johnson, S.R.; Zhang, Y.-H.
2002-01-01
We discuss the growth by molecular-beam epitaxy, and studies of the low-temperature electrical properties, of undoped InAs/AlSb quantum wells. The two-dimensional electron gas realized in the wells exhibits high mobility at low temperatures, and an analysis of its Shubnikov-de Haas oscillations suggests this mobility is limited by scattering from remotely located unintentional dopants. Spin splitting of the oscillations is clearly resolved at 4.2 K, revealing a g-factor as large as -60 at high magnetic fields. The size of this enhancement increases with decreasing electron density, and is thought to reflect the associated increase in the strength of the effective Coulomb interaction
Energy Technology Data Exchange (ETDEWEB)
Zhang, Shukui [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Poelker, Matthew [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Stutzman, Marcy L. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Chen, Yiqiao [SVT Associates, Inc., Eden Prairie, MN (United States); Moy, Aaron [SVT Associates, Inc., Eden Prairie, MN (United States)
2015-09-01
Polarized photocathodes with higher Quantum efficiency (QE) would help to reduce the technological challenge associated with producing polarized beams at milliampere levels, because less laser light would be required, which simplifies photocathode cooling requirements. And for a given amount of available laser power, higher QE would extend the photogun operating lifetime. The distributed Bragg reflector (DBR) concept was proposed to enhance the QE of strained-superlattice photocathodes by increasing the absorption of the incident photons using a Fabry-Perot cavity formed between the front surface of the photocathode and the substrate that includes a DBR, without compromising electron polarization. Here we present recent results showing QE enhancement of a GaAs/GaAsP strained-superlattice photocathode made with a DBR structure. Typically, a GaAs/GaAsP strained-superlattice photocathode without DBR provides a QE of 1%, at a laser wavelength corresponding to peak polarization. In comparison, the GaAs/GaAsP strained-superlattice photocathodes with DBR exhibited an enhancement of over 2 when the incident laser wavelength was tuned to meet the resonant condition for the Fabry-Perot resonator.
Enhanced Anion Transport Using Some Expanded Porphyrins as Carriers.
1991-01-01
many others who provided me with invaluable and much needed help. Miguel Rosingana, Kevin Boudreaux, Micheal Cyr, Dr. Tony Burrell, and Kevin Shredder ...channel in erythrocytes; and the so-called ATP/ADP exchanger. 19 A breakdown in the mediated transport of an essential metabolqtes can be detrimental. For
Enhanced water transport and salt rejection through hydrophobic zeolite pores
Humplik, Thomas; Lee, Jongho; O’Hern, Sean; Laoui, Tahar; Karnik, Rohit; Wang, Evelyn N.
2017-12-01
The potential of improvements to reverse osmosis (RO) desalination by incorporating porous nanostructured materials such as zeolites into the selective layer in the membrane has spurred substantial research efforts over the past decade. However, because of the lack of methods to probe transport across these materials, it is still unclear which pore size or internal surface chemistry is optimal for maximizing permeability and salt rejection. We developed a platform to measure the transport of water and salt across a single layer of zeolite crystals, elucidating the effects of internal wettability on water and salt transport through the ≈5.5 Å pores of MFI zeolites. MFI zeolites with a more hydrophobic (i.e., less attractive) internal surface chemistry facilitated an approximately order of magnitude increase in water permeability compared to more hydrophilic MFI zeolites, while simultaneously fully rejecting both potassium and chlorine ions. However, our results also demonstrated approximately two orders of magnitude lower permeability compared to molecular simulations. This decreased performance suggests that additional transport resistances (such as surface barriers, pore collapse or blockages due to contamination) may be limiting the performance of experimental nanostructured membranes. Nevertheless, the inclusion of hydrophobic sub-nanometer pores into the active layer of RO membranes should improve both the water permeability and salt rejection of future RO membranes (Fasano et al 2016 Nat. Commun. 7 12762).
Persistent wind-induced enhancement of diffusive CO2 transport in a mountain forest snowpack
D. R. Bowling; W. J. Massman
2011-01-01
Diffusion dominates the transport of trace gases between soil and the atmosphere. Pressure gradients induced by atmospheric flow and wind interacting with topographical features cause a small but persistent bulk flow of air within soil or snow. This forcing, called pressure pumping or wind pumping, leads to a poorly quantified enhancement of gas transport beyond the...
A Study of Vertical Transport through Graphene toward Control of Quantum Tunneling.
Zhu, Xiaodan; Lei, Sidong; Tsai, Shin-Hung; Zhang, Xiang; Liu, Jun; Yin, Gen; Tang, Min; Torres, Carlos M; Navabi, Aryan; Jin, Zehua; Tsai, Shiao-Po; Qasem, Hussam; Wang, Yong; Vajtai, Robert; Lake, Roger K; Ajayan, Pulickel M; Wang, Kang L
2018-02-14
Vertical integration of van der Waals (vdW) materials with atomic precision is an intriguing possibility brought forward by these two-dimensional (2D) materials. Essential to the design and analysis of these structures is a fundamental understanding of the vertical transport of charge carriers into and across vdW materials, yet little has been done in this area. In this report, we explore the important roles of single layer graphene in the vertical tunneling process as a tunneling barrier. Although a semimetal in the lateral lattice plane, graphene together with the vdW gap act as a tunneling barrier that is nearly transparent to the vertically tunneling electrons due to its atomic thickness and the transverse momenta mismatch between the injected electrons and the graphene band structure. This is accentuated using electron tunneling spectroscopy (ETS) showing a lack of features corresponding to the Dirac cone band structure. Meanwhile, the graphene acts as a lateral conductor through which the potential and charge distribution across the tunneling barrier can be tuned. These unique properties make graphene an excellent 2D atomic grid, transparent to charge carriers, and yet can control the carrier flux via the electrical potential. A new model on the quantum capacitance's effect on vertical tunneling is developed to further elucidate the role of graphene in modulating the tunneling process. This work may serve as a general guideline for the design and analysis of vdW vertical tunneling devices and heterostructures, as well as the study of electron/spin injection through and into vdW materials.
Theory of classical and quantum transport in monolayers of MoS2
Adam, Shaffique
From the family of new van der Waals materials, the class of layered transition metal dichalcogenides has emerged as a particularly interesting system due to the inherent spin and valley degrees of freedom. In this talk we focus on the interplay between these degrees of freedom and the different types of disorder in monolayers of molybdenum disulphide. Within the semiclassical Drude-Boltzmann formalism, treating the screening of impurities with the random phase approximation, we demonstrate that different scattering mechanisms such as charged impurity scattering, intervalley scattering, and phonons provide different signatures in electronic transport. This allows us to conclude, for example, that in CVD-grown monolayers of MoS2, intervalley scattering dominates over other mechanisms at low temperatures. Interestingly, charged impurities generate spatial inhomogeneity in the carrier density that results in a classical disorder-induced magnetoresistance that can be observed at room temperature. However, at lower temperatures, in this regime of strong intervalley scattering, we predict that the quantum phase-coherent corrections to the conductivity results in a one-parameter crossover from weak localization to weak anti-localization as a function of magnetic field, where this crossover is determined only by the spin lifetime. By comparing with available experimental data, we show that this combined framework allows for a novel way to measure the spin-relaxation in monolayers of MoS2. We find that the spin scattering arises from the Dyakonov-Perel spin-orbit scattering mechanism with a conduction band spin-splitting of about 4 meV, consistent with calculations using density functional theory. Work done in collaboration with Indra Yudhistira and the experimental groups of Goki Eda (NUS), Michael Fuhrer (Monash) and Roland Kawakami (Ohio State), and funded by Singapore National Research Foundation and Ministry of Education.
Spin transport in the two-dimensional quantum disordered anisotropic Heisenberg model
Energy Technology Data Exchange (ETDEWEB)
Lima, L.S. [Departamento de Física e Matemática, Centro Federal de Educação Tecnológica de Minas Gerais, 30510-000 Belo Horizonte, MG (Brazil); Pires, A.S.T.; Costa, B.V. [Departamento de Física ICEx, UFMG, CP 702, 31270-901 Belo Horizonte, MG (Brazil)
2014-12-15
We use the self consistent harmonic approximation together with the Linear Response Theory to study the effect of nonmagnetic disorder on spin transport in the quantum diluted two-dimensional anisotropic Heisenberg model with spin S=1 in a square lattice. The model has a BKT transition at zero dilution. We calculate the regular part of the spin conductivity σ{sup reg}(ω) and the Drude weight D{sub S}(T) as a function of the non-magnetic concentration, x. Our calculations show that the spin conductivity drops abruptly to zero at x{sub c}{sup SCHA}≈0.5 indicating that the system changes from an ideal spin conductor state to an insulator. This value is far above the site percolation threshold x{sub c}{sup site}≈0.41. Although the SCHA fails in determining precisely the percolation threshold, both the spin conductivity and the Drude weight show a quite regular behavior inside 0≤x≤x{sub c}{sup SCHA} indicating that the transition stays in the same universality class all along the interval. - Highlights: • The site dilution generates a large influence on regular part of the spin conductivity, σ{sup reg}(ω), and in the Drude weight, D(T). • In a concentration of impurities about x≈0.5, the regular part of the spin conductivity and the Drude weight fall to zero. • In this point we have a change in the state of the system from an ideal spin conductor to a spin insulator.
Muñoz-García, Ana B; Ritzmann, Andrew M; Pavone, Michele; Keith, John A; Carter, Emily A
2014-11-18
CONSPECTUS: Global advances in industrialization are precipitating increasingly rapid consumption of fossil fuel resources and heightened levels of atmospheric CO2. World sustainability requires viable sources of renewable energy and its efficient use. First-principles quantum mechanics (QM) studies can help guide developments in energy technologies by characterizing complex material properties and predicting reaction mechanisms at the atomic scale. QM can provide unbiased, qualitative guidelines for experimentally tailoring materials for energy applications. This Account primarily reviews our recent QM studies of electrode materials for solid oxide fuel cells (SOFCs), a promising technology for clean, efficient power generation. SOFCs presently must operate at very high temperatures to allow transport of oxygen ions and electrons through solid-state electrolytes and electrodes. High temperatures, however, engender slow startup times and accelerate material degradation. SOFC technologies need cathode and anode materials that function well at lower temperatures, which have been realized with mixed ion-electron conductor (MIEC) materials. Unfortunately, the complexity of MIECs has inhibited the rational tailoring of improved SOFC materials. Here, we gather theoretically obtained insights into oxygen ion conductivity in two classes of perovskite-type materials for SOFC applications: the conventional La1-xSrxMO3 family (M = Cr, Mn, Fe, Co) and the new, promising class of Sr2Fe2-xMoxO6 materials. Using density functional theory + U (DFT+U) with U-J values obtained from ab initio theory, we have characterized the accompanying electronic structures for the two processes that govern ionic diffusion in these materials: (i) oxygen vacancy formation and (ii) vacancy-mediated oxygen migration. We show how the corresponding macroscopic oxygen diffusion coefficient can be accurately obtained in terms of microscopic quantities calculated with first-principles QM. We find that the
3D Topography Design of Membranes for Enhanced Mass Transport
Czech Academy of Sciences Publication Activity Database
Izák, Pavel; Godinho, M.H.; Brogueira, P.; Figueirinhas, J.L.; Crespo, J.G.
2008-01-01
Roč. 321, č. 2 (2008), s. 337-343 ISSN 0376-7388 R&D Projects: GA ČR GA104/08/0600 Grant - others:SFRH(PT) BPD/9470/2002; POCTI(PT) EQU/35437/2000; POCTI(PT) CTM/56382/2004 Institutional research plan: CEZ:AV0Z40720504 Keywords : Ionic liquids * mass transport * pervaporation Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 3.247, year: 2008
Debellis, Doriana; Gigli, Giuseppe; Ten Brinck, Stephanie; Infante, Ivan; Giansante, Carlo
2017-01-01
Nowadays it is well-accepted to attribute bulk-like optical absorption properties to colloidal PbS quantum dots (QDs) at wavelengths above 400 nm. This assumption permits to describe PbS QD light absorption by using bulk optical constants and to determine QD concentration in colloidal solutions from
Zhang, Ya-Jing; Zhang, Lian-Lian; Jiang, Cui; Gong, Wei-Jiang
2018-02-01
We theoretically investigate the electronic transport through a parallel-coupled multi-quantum-dot system, in which the terminal dots of a one-dimensional quantum-dot chain are embodied in the two arms of an Aharonov-Bohm interferometer. It is found that in the structures of odd(even) dots, all their even(odd) molecular states have opportunities to decouple from the leads, and in this process antiresonance occurs which are accordant with the odd(even)-numbered eigenenergies of the sub-molecule without terminal dots. Next when Majorana zero modes are introduced to couple laterally to the terminal dots, the antiresonance and decoupling phenomena still co-exist in the quantum transport process. Such a result can be helpful in understanding the special influence of Majorana zero mode on the electronic transport through quantum-dot systems.
Enhancement of In Vitro Skin Transport and In Vivo Hypoglycemic ...
African Journals Online (AJOL)
Abstract. Purpose: To utilize hydroxybutyl-β-cyclodextrin (HB-β-CD) and polyvinyl pyrrolidone (PVP) for the enhancement of the transdermal delivery of glimepiride (GMD). Methods: Matrix-type transdermal patches containing GMD, drug coprecipitate or its inclusion complex were prepared using different gelling agents, viz, ...
Combining surface plasmonic and light extraction enhancement on InGaN quantum-well light-emitters
DEFF Research Database (Denmark)
Fadil, Ahmed; Ou, Yiyu; Iida, Daisuke
2016-01-01
and internal quantum efficiency enhancement for InGaN/GaN quantum-well light-emitters. By fabricating dielectric nano-rod pattern on the GaN surface, an optical coating that improves the light extraction is obtained, and furthermore has a low refractive index which blue-shifts the plasmonic resonance of Ag NPs......Surface plasmon coupling with light-emitters and surface nano-patterning have widely been used separately to improve low efficiency InGaN light-emitting diodes. We demonstrate a method where dielectric nano-patterning and Ag nanoparticles (NPs) are combined to provide both light extraction...
Quantum-Noise-Limited Sensitivity Enhancement of a Passive Optical Cavity by a Fast-Light Medium
Smith, David D.; Luckay, H. A.; Chang, Hongrok; Myneni, Krishna
2016-01-01
We demonstrate for a passive optical cavity containing a dispersive atomic medium, the increase in scale factor near the critical anomalous dispersion is not cancelled by mode broadening or attenuation, resulting in an overall increase in the predicted quantum-noise-limited sensitivity. Enhancements of over two orders of magnitude are measured in the scale factor, which translates to greater than an order-of-magnitude enhancement in the predicted quantum-noise-limited measurement precision, by temperature tuning a low-pressure vapor of non-interacting atoms in a low-finesse cavity close to the critical anomalous dispersion condition. The predicted enhancement in sensitivity is confirmed through Monte-Carlo numerical simulations.
Muñoz-Rosas, Ana Luz; Rodríguez-Gómez, Arturo; Alonso-Huitrón, Juan Carlos
2018-03-22
Nowadays, the use of plasmonic metal layers to improve the photonic emission characteristics of several semiconductor quantum dots is a booming tool. In this work, we report the use of silicon quantum dots (SiQDs) embedded in a silicon nitride thin film coupled with an ultra-thin gold film (AuNPs) to fabricate light emitting devices. We used the remote plasma enhanced chemical vapor deposition technique (RPECVD) in order to grow two types of silicon nitride thin films. One with an almost stoichiometric composition, acting as non-radiative spacer; the other one, with a silicon excess in its chemical composition, which causes the formation of silicon quantum dots imbibed in the silicon nitride thin film. The ultra-thin gold film was deposited by the direct current (DC)-sputtering technique, and an aluminum doped zinc oxide thin film (AZO) which was deposited by means of ultrasonic spray pyrolysis, plays the role of the ohmic metal-like electrode. We found that there is a maximum electroluminescence (EL) enhancement when the appropriate AuNPs-spacer-SiQDs configuration is used. This EL is achieved at a moderate turn-on voltage of 11 V, and the EL enhancement is around four times bigger than the photoluminescence (PL) enhancement of the same AuNPs-spacer-SiQDs configuration. From our experimental results, we surmise that EL enhancement may indeed be due to a plasmonic coupling. This kind of silicon-based LEDs has the potential for technology transfer.
Directory of Open Access Journals (Sweden)
Ana Luz Muñoz-Rosas
2018-03-01
Full Text Available Nowadays, the use of plasmonic metal layers to improve the photonic emission characteristics of several semiconductor quantum dots is a booming tool. In this work, we report the use of silicon quantum dots (SiQDs embedded in a silicon nitride thin film coupled with an ultra-thin gold film (AuNPs to fabricate light emitting devices. We used the remote plasma enhanced chemical vapor deposition technique (RPECVD in order to grow two types of silicon nitride thin films. One with an almost stoichiometric composition, acting as non-radiative spacer; the other one, with a silicon excess in its chemical composition, which causes the formation of silicon quantum dots imbibed in the silicon nitride thin film. The ultra-thin gold film was deposited by the direct current (DC-sputtering technique, and an aluminum doped zinc oxide thin film (AZO which was deposited by means of ultrasonic spray pyrolysis, plays the role of the ohmic metal-like electrode. We found that there is a maximum electroluminescence (EL enhancement when the appropriate AuNPs-spacer-SiQDs configuration is used. This EL is achieved at a moderate turn-on voltage of 11 V, and the EL enhancement is around four times bigger than the photoluminescence (PL enhancement of the same AuNPs-spacer-SiQDs configuration. From our experimental results, we surmise that EL enhancement may indeed be due to a plasmonic coupling. This kind of silicon-based LEDs has the potential for technology transfer.
International Nuclear Information System (INIS)
Yan Junxia; Fu Huahua
2013-01-01
We study the electronic transport through a four-quantum-dot (FQD) structure with a diamond-like shape through nonequilibrium Green's function theory. It is observed that the bound state in the continuum (BIC) appears in this multiple QDs system, and the position of the BIC in the total density of states (TDOS) spectrum is tightly determined by the strength of the electronic hopping between the upper QD and the lower one. As the symmetry in the energy levels in these two QDs is broken, the BIC is suppressed to a general conductance peak with a finite width, and meanwhile a Fano-type antiresonance with a zero point appears in the conductance spectrum. These results will develop our understanding of the BICs and their spintronic device applications of spin filter and quantum computing.
Enhancing Quantum Discord in Cavity QED by Applying Classical Driving Field
International Nuclear Information System (INIS)
Qian Yi; Xu Jing-Bo
2012-01-01
We investigate the quantum discord dynamics in a cavity quantum electrodynamics system, which consists of two noninteracting two-level atoms driven by independent optical fields and classical fields, and find that the quantum discord vanishes only asymptotically although entanglement disappears suddenly during the time evolution in the absence of classical fields. It is shown that the amount of quantum discord can be increased by adjusting the classical driving fields because the increasing degree of the amount of quantum mutual information is greater than classical correlation by applying the classical driving fields. Finally, the influence of the classical driving field on the fidelity of the system is also examined. (general)
Enhanced performance of hybrid solar cells using longer arms of quantum cadmium selenide tetrapods
Lee, Kyu-Sung
2011-12-01
We demonstrate that enhanced device performance of hybrid solar cells based on tetrapod (TP)-shaped cadmium selenide (CdSe) nanoparticles and conjugated polymer of poly (3-hexylthiophene) (P3HT) can be obtained by using longer armed tetrapods which aids in better spatial connectivity, thus decreasing charge hopping events which lead to better charge transport. Longer tetrapods with 10 nm arm length lead to improved power conversion efficiency of 1.12% compared to 0.80% of device having 5 nm short-armed tetrapods:P3HT photoactive blends.
International Nuclear Information System (INIS)
Lee, S.H.; Lee, J.T.; Sug, J.Y.; Lee, J.H.; Sa-Gong, G.
2011-01-01
We investigated theoretically the magnetic field dependence of the quantum optical transition of quasi 2-Dimensional Landau splitting system, in CdS and ZnO. Through the analysis of the current work, we found the increasing properties of the optical Quantum Transition Line Shapes (QTLSs) which show the absorption power and the Quantum Transition Line Widths(QTLWs) with the magnetic-field in CdS and ZnO. We also found that QTLW, γ(B) total of CdS total of ZnO in the magnetic field region B < 25 Tesla.
Energy Technology Data Exchange (ETDEWEB)
Wang, Xiaoxia [State Key Laboratory of Materials and Processing Die & Mould Technology, Nanomaterials and Smart Sensors Research Laboratory, Department of Materials Science and Engineering, Huazhong University of Science and Technology, No. 1037, Luoyu Road, Wuhan 430074 (China); Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Wuhan 430062 (China); Ni, Qian [State Key Laboratory of Materials and Processing Die & Mould Technology, Nanomaterials and Smart Sensors Research Laboratory, Department of Materials Science and Engineering, Huazhong University of Science and Technology, No. 1037, Luoyu Road, Wuhan 430074 (China); Zeng, Dawen, E-mail: dwzeng@mail.hust.edu.cn [State Key Laboratory of Materials and Processing Die & Mould Technology, Nanomaterials and Smart Sensors Research Laboratory, Department of Materials Science and Engineering, Huazhong University of Science and Technology, No. 1037, Luoyu Road, Wuhan 430074 (China); Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Wuhan 430062 (China); Liao, Guanglan [State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, No. 1037, Luoyu Road, Wuhan 430074 (China); Xie, Changsheng [State Key Laboratory of Materials and Processing Die & Mould Technology, Nanomaterials and Smart Sensors Research Laboratory, Department of Materials Science and Engineering, Huazhong University of Science and Technology, No. 1037, Luoyu Road, Wuhan 430074 (China)
2016-12-15
Highlights: • Charge separation in homojunction based on the broadened band gap by quantum effect. • Absolute charge separation by the passivation effect of TiO{sub 2} nanorod. • Long-distance electron transfer behavior in photocatalysis. • Roughed surface for enhanced light harvesting by light trapping effect. - Abstract: As known, the electron transfer behavior in photocatalysis is short-distance transportation, which leads the photo-induced electrons and holes to be localized. The temporarily separated electrons and holes will recombine with each other in the localized region. In this paper, we successfully achieved electron transfer in a homojunction of branched rutile TiO{sub 2} nanorod @nanoparticle core-shell architecture by quantum confinement effect aroused by the nanoparticle, which is proved by the blue-shifting in UV–vis absorption spectrum of the homojunction. Meanwhile, an absolute charge separation is also achieved by the long-distance electron transfer along the single-crystalline rutile TiO{sub 2} nanorod as uninterrupted high-speed electron transfer channel to FTO substrates. Based on the effective charge separation, the photocatalytic decomposition of gaseous benzene by the homojunction is significantly enhanced, yielding 10 times CO{sub 2} than that of the nanorod array. This homojunction interfacial charge separation, aroused by quantum effect, through long-distance transfer along the single-crystalline nanorod gives us inspiration to achieve efficient charge separation with defect-less interfaces, which might can be utilized for real-time environmental abatement and energy generation simultaneously.
Pfeiffer, P.; Egusquiza, I. L.; Di Ventra, M.; Sanz, M.; Solano, E.
2016-01-01
Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems. PMID:27381511
Quantum-Noise-Limited Sensitivity-Enhancement of a Passive Optical Cavity by a Fast-Light Medium
Smith, David D.; Luckay, H. A.; Chang, Hongrok; Myneni, Krishna
2016-01-01
We demonstrate for a passive optical cavity containing an intracavity dispersive atomic medium, the increase in scale factor near the critical anomalous dispersion is not cancelled by mode broadening or attenuation, resulting in an overall increase in the predicted quantum-noiselimited sensitivity. Enhancements of over two orders of magnitude are measured in the scale factor, which translates to greater than an order-of-magnitude enhancement in the predicted quantumnoise- limited measurement precision, by temperature tuning a low-pressure vapor of noninteracting atoms in a low-finesse cavity close to the critical anomalous dispersion condition. The predicted enhancement in sensitivity is confirmed through Monte-Carlo numerical simulations.
International Nuclear Information System (INIS)
Guan, Chun; Xing, Yunhui; Zhang, Chao; Ma, Zhongshui
2014-01-01
Due to quantum interference, light can transmit through dense atomic media, a phenomenon known as electromagnetically induced transparency (EIT). We propose that EIT is not limited to light transmission and there is an electronic analog where resonant transparency in charge transport in an opaque structure can be induced by electromagnetic radiation. A triple-quantum-dots system with Λ-type level structure is generally opaque due to the level in the center dot being significantly higher and therefore hopping from the left dot to the center dot is almost forbidden. We demonstrate that an electromagnetically induced electron transparency (EIET) in charge of transport can indeed occur in the Λ-type system. The direct evidence of EIET is that an electron can travel from the left dot to the right dot, while the center dot apparently becomes invisible. We analyze EIET and the related shot noise in both the zero and strong Coulomb blockade regimes. It is found that the EIET (position, height, and symmetry) can be tuned by several controllable parameters of the radiation fields, such as the Rabi frequencies and detuning frequencies. The result offers a transparency/opaque tuning technique in charge transport using interfering radiation fields
The features of ballistic electron transport in a suspended quantum point contact
International Nuclear Information System (INIS)
Shevyrin, A. A.; Budantsev, M. V.; Bakarov, A. K.; Toropov, A. I.; Pogosov, A. G.; Ishutkin, S. V.; Shesterikov, E. V.
2014-01-01
A suspended quantum point contact and the effects of the suspension are investigated by performing identical electrical measurements on the same experimental sample before and after the suspension. In both cases, the sample demonstrates conductance quantization. However, the suspended quantum point contact shows certain features not observed before the suspension, namely, plateaus at the conductance values being non-integer multiples of the conductance quantum, including the “0.7-anomaly.” These features can be attributed to the strengthening of electron-electron interaction because of the electric field confinement within the suspended membrane. Thus, the suspended quantum point contact represents a one-dimensional system with strong electron-electron interaction
Enhancing of optic phonon contribution in hydrodynamic phonon transport
de Tomas, C.; Cantarero, A.; Lopeandia, A. F.; Alvarez, F. X.
2015-10-01
In the framework of the kinetic-collective model of phonon heat transport, we analyze how each range of the phonon frequency spectrum contributes to the total thermal conductivity both in the macro and the nanoscale. For this purpose, we use two case study samples: naturally occurring bulk silicon and a 115 nm of diameter silicon nanowire. We show that the contribution of high-energy phonons (optic branches) is non-negligible only when N-collisions are strongly present. This contribution increases when the effective size of the sample decreases, and it is found to be up to a 10% at room temperature for the 115 nm nanowire, corroborating preliminar ab-initio predictions.
Quantum field kinetics of QCD quark-gluon transport theory for light-cone dominated processes
Kinder-Geiger, Klaus
1996-01-01
A quantum kinetic formalism is developed to study the dynamical interplay of quantum and statistical-kinetic properties of non-equilibrium multi-parton systems produced in high-energy QCD processes. The approach provides the means to follow the quantum dynamics in both space-time and energy-momentum, starting from an arbitrary initial configuration of high-momentum quarks and gluons. Using a generalized functional integral representation and adopting the `closed-time-path' Green function techniques, a self-consistent set of equations of motions is obtained: a Ginzburg-Landau equation for a possible color background field, and Dyson-Schwinger equations for the 2-point functions of the gluon and quark fields. By exploiting the `two-scale nature' of light-cone dominated QCD processes, i.e. the separation between the quantum scale that specifies the range of short-distance quantum fluctuations, and the kinetic scale that characterizes the range of statistical binary inter- actions, the quantum-field equations of ...
Singh, Madhav K.; Jha, Pradeep K.; Bhattacherjee, Aranya B.
2017-09-01
In this article, we study the spin and tunneling dynamics as a function of magnetic field in a one-dimensional GaAs double quantum dot with both the Dresselhaus and Rashba spin-orbit coupling. In particular, we consider different spatial widths for the spin-up and spin-down electronic states. We find that the spin dynamics is a superposition of slow as well as fast Rabi oscillations. It is found that the Rashba interaction strength as well as the external magnetic field strongly modifies the slow Rabi oscillations which is particularly useful for implementing solid state selective spin transport device.
Tang, Chi-Shung; Tseng, Shu-Ting; Gudmundsson, Vidar; Cheng, Shun-Jen
2015-03-04
We investigate double finger gate (DFG) controlled spin-resolved resonant transport properties in an n-type quantum channel with a Rashba-Zeeman (RZ) subband energy gap. By appropriately tuning the DFG in the strong Rashba coupling regime, resonant state structures in conductance can be found that are sensitive to the length of the DFG system. Furthermore, a hole-like bound state feature below the RZ gap and an electron-like quasi-bound state feature at the threshold of the upper spin branch can be found that is insensitive to the length of the DFG system.
Quantum information processing : science & technology.
Energy Technology Data Exchange (ETDEWEB)
Horton, Rebecca; Carroll, Malcolm S.; Tarman, Thomas David
2010-09-01
Qubits demonstrated using GaAs double quantum dots (DQD). The qubit basis states are the (1) singlet and (2) triplet stationary states. Long spin decoherence times in silicon spurs translation of GaAs qubit in to silicon. In the near term the goals are: (1) Develop surface gate enhancement mode double quantum dots (MOS & strained-Si/SiGe) to demonstrate few electrons and spin read-out and to examine impurity doped quantum-dots as an alternative architecture; (2) Use mobility, C-V, ESR, quantum dot performance & modeling to feedback and improve upon processing, this includes development of atomic precision fabrication at SNL; (3) Examine integrated electronics approaches to RF-SET; (4) Use combinations of numerical packages for multi-scale simulation of quantum dot systems (NEMO3D, EMT, TCAD, SPICE); and (5) Continue micro-architecture evaluation for different device and transport architectures.
In situ surface-enhanced Raman spectroscopy effect in zeolite due to Ag2Se quantum dots
International Nuclear Information System (INIS)
Martinez-Nuñez, C. E.; Cortez-Valadez, M.; Delgado-Beleño, Y.; Flores-López, N. S.; Román-Zamorano, J. F.; Flores-Valenzuela, J.; Flores-Acosta, M.
2017-01-01
This study shows the presence of surface-enhanced Raman spectroscopy (SERS) effect caused by Ag 2 Se quantum dots embedded in the zeolite matrix. The quantum dots that were synthesised and stabilised in the matrix of F9-NaX zeolite show a size of 5 nm and a quasi-spherical morphology. The calculated interplanar distances confirm the presence of quantum dots in cubic phase Im-m. We suppose that the in situ SERS effect in the material is caused by chemical-enhancement mechanism (CEM). The density functional theory (DFT) is undertaken to corroborate our hypothesis. The structure H 8 Si 8 Al 8 O 12 represents the zeolite cavity unit, and small clusters of (Ag 2 Se) n represent the quantum dots. Both structures interact in the cavity to obtain the local minimum of the potential energy surface, leading to new molecular orbitals. After the analysis of the predicted Raman spectrum, the Raman bands increase significantly, agreeing with the experimental results at low wavenumbers in F9-NaX zeolite.
In situ surface-enhanced Raman spectroscopy effect in zeolite due to Ag{sub 2}Se quantum dots
Energy Technology Data Exchange (ETDEWEB)
Martinez-Nuñez, C. E. [Universidad de Sonora, Departamento de Investigación en Física (Mexico); Cortez-Valadez, M., E-mail: jose.cortez@unison.mx, E-mail: manuelcortez@live.com [Universidad de Sonora, CONACYT-Departamento de Investigación en Física (Mexico); Delgado-Beleño, Y.; Flores-López, N. S. [Universidad de Sonora, Departamento de Investigación en Física (Mexico); Román-Zamorano, J. F. [Centro de Investigación y Desarrollo Tecnológico en Electroquímica (Mexico); Flores-Valenzuela, J. [Universidad Autónoma de Sinaloa (Mexico); Flores-Acosta, M. [Universidad de Sonora, Departamento de Investigación en Física (Mexico)
2017-02-15
This study shows the presence of surface-enhanced Raman spectroscopy (SERS) effect caused by Ag{sub 2}Se quantum dots embedded in the zeolite matrix. The quantum dots that were synthesised and stabilised in the matrix of F9-NaX zeolite show a size of 5 nm and a quasi-spherical morphology. The calculated interplanar distances confirm the presence of quantum dots in cubic phase Im-m. We suppose that the in situ SERS effect in the material is caused by chemical-enhancement mechanism (CEM). The density functional theory (DFT) is undertaken to corroborate our hypothesis. The structure H{sub 8}Si{sub 8}Al{sub 8}O{sub 12} represents the zeolite cavity unit, and small clusters of (Ag{sub 2}Se){sub n} represent the quantum dots. Both structures interact in the cavity to obtain the local minimum of the potential energy surface, leading to new molecular orbitals. After the analysis of the predicted Raman spectrum, the Raman bands increase significantly, agreeing with the experimental results at low wavenumbers in F9-NaX zeolite.
Qin, Jing-Kai; Ren, Dan-Dan; Shao, Wen-Zhu; Li, Yang; Miao, Peng; Sun, Zhao-Yuan; Hu, PingAn; Zhen, Liang; Xu, Cheng-Yan
2017-11-15
ReS 2 films are considered as a promising candidate for optoelectronic applications due to their direct band gap character and optical/electrical anisotropy. However, the direct band gap in a narrow spectrum and the low absorption of atomically thin flakes weaken the prospect for light-harvesting applications. Here, we developed an efficient approach to enhance the performance of a ReS 2 -based phototransistor by coupling CdSe-CdS-ZnS core-shell quantum dots. Under 589 nm laser irradiation, the responsivity of the ReS 2 phototransistor decorated with quantum dots could be enhanced by more than 25 times (up to ∼654 A/W) and the rising and recovery time can be also reduced to 3.2 and 2.8 s, respectively. The excellent optoelectronic performance is originated from the coupling effect of quantum dots light absorber and cross-linker ligands 1,2-ethanedithiol. Photoexcited electron-hole pairs in quantum dots can separate and transfer efficiently due to the type-II band alignment and charge exchange process at the interface. Our work shows that the simple hybrid zero- and two-dimensional hybrid system can be employed for photodetection applications.
Reclaimed wastewater quality enhancement by oxygen injection during transportation.
Rodríguez-Gómez, L E; Alvarez, M; Rodríguez-Sevilla, J; Marrero, M C; Hernández, A
2011-01-01
In-sewer treatments have been studied in sewer systems, but few have been carried out on reclaimed wastewater systems. A study of oxygen injection has been performed in a completely filled gravity pipe, 0.6 m in diameter and 62 km long, in cast iron with concrete inside coating, which is part of the reclaimed wastewater reuse scheme of Tenerife (Spain). A high pressure oxygen injection system was installed at 16.0 km from pipe inlet and a constant dosage of 30 mg/L O(2) has been injected during six months, under three different operational modes (low COD, 63 mg/L; high COD, 91 mg/L; and partially nitrified water). Oxygen has been consumed in nitrification and organic matter reduction. Generally, nitrification is clearly favored instead of the organic matter oxidation. Nitrification occurs, in general, with nitrite accumulation due to the presence of free ammonia above 1 mg/L. Denitrification is in all cases incomplete due to a limitation of easily biodegradable organic matter content, inhibiting the appearance of anaerobic conditions and sulfide generation. A notable reduction of organic matter parameters is achieved (TSS below 10 mg/L), which is significantly higher than that observed under the ordinary transport conditions without oxygen. This leads to a final cost reduction, and the oxygen injection system helps water reuse managers to maintain a final good water quality in the case of a treatment plant malfunction.
Energy Technology Data Exchange (ETDEWEB)
Hensen, Matthias [Institut; Heilpern, Tal [Center; Gray, Stephen K. [Center; Pfeiffer, Walter [Fakultät
2017-10-12
Establishing strong coupling between spatially separated and thus selectively addressable quantum emitters is a key ingredient to complex quantum optical schemes in future technologies. Insofar as many plasmonic nanostructures are concerned, however, the energy transfer and mutual interaction strength between distant quantum emitters can fail to provide strong coupling. Here, based on mode hybridization, the longevity and waveguide character of an elliptical plasmon cavity are combined with intense and highly localized field modes of suitably designed nanoantennas. Based on FDTD simulations a quantum emitter-plasmon coupling strength hg = 16.7 meV is reached while simultaneously keeping a small plasmon resonance line width h gamma(s) = 33 meV. This facilitates strong coupling, and quantum dynamical simulations reveal an oscillatory exchange of excited state population arid a notable degree of entanglement between the quantum emitters spatially separated by 1.8 mu m, i.e., about twice the operating wavelength.
Payette, Christopher
2011-12-01
Performing transport measurements on weakly coupled vertical double quantum dots, we study by magneto-resonant-tunneling spectroscopy, single-particle energy spectra of the constituent dots over a wide energy window. The measured energy spectra are well modeled overall by ideal spectra calculated for elliptical and parabolic in-dot-plane confinement potentials. However, in regions where single-particle energy levels are naively expected to cross, we observe pronounced level anti-crossing behaviour and strong resonant current variations (both enhancement and suppression). Within a coherent tunneling picture, these effects can be attributed to coherent level mixing induced by weak perturbations in the nearly ideal dot confinement potentials. We analyze the energy spectra in detail, and focus on examples of two-, three- and four-level crossings where we observe the suppression of an otherwise strong current resonance, a signature of dark state formation due to destructive interference. The mixing we measure and model at two three-level crossings represents an all-electrical analogue of coherent population trapping. We also explore the limitations of the applicability of the coherent level mixing model and demonstrate in-situ alteration of the coupling between levels. We further examine the electron spin-nuclear spin (hyperfine) interaction. In the familiar two-electron spin blockade regime, on application of an out-of-dot-plane magnetic field, we observe current switching and hysteresis, and a funnel-like structure in the leakage current, all hallmarks of the hyperfine interaction. The measurements bring to light a strong gate voltage dependence, significant device-to-device variations, and an intricate bias voltage history dependence not accounted for in any existing model. Unexpectedly, we also observe signatures of the hyperfine interaction at high bias, well outside the spin blockade regime. We characterize these features and suggest how the hyperfine interaction
Theory of single quantum dot lasers: Pauli-blocking-enhanced anti-bunching
International Nuclear Information System (INIS)
Su, Yumian; Bimberg, Dieter; Carmele, Alexander; Richter, Marten; Knorr, Andreas; Lüdge, Kathy; Schöll, Eckehard
2011-01-01
We present a theoretical model to describe the dynamics of a single semiconductor quantum dot interacting with a microcavity system. The confined quantum dot levels are pumped electrically via a carrier reservoir. The investigated dynamics includes semiconductor-specific, reservoir-induced Pauli-blocking terms in the equations of the photon probability functions. This enables a direct study of the photon statistics of the quantum light emission in dependence on the different pumping rates
Energy Technology Data Exchange (ETDEWEB)
Shkolnik, A. S., E-mail: alix@mbepl.ioffe.ru [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation); Savelyev, A. V. [St. Petersburg State Polytechnical University (Russian Federation); Karachinsky, L. Ya.; Gordeev, N. Yu.; Seisyan, R. P.; Zegrya, G. G. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation); Pellegrini, S.; Buller, G. S. [Heriot-Watt University, School of Engineering and Physical Science (United Kingdom); Evtikhiev, V. P. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)
2008-03-15
The results of time-resolved photoluminescence studies of heterostructures containing monolayer arrays of InAs/GaAs quantum dots are presented. A two-component time dependence of intensity of photoluminescence from the ground state of quantum dots, with characteristic times of the slow component up to hundreds of nanoseconds and those of rapid one several nanoseconds, is studied. It is shown that the slow component is determined by the transport of nonequilibrium charge carriers between the quantum dots. At low temperatures, the time of the slow component is determined by tunneling, and at high temperatures by thermal escape of nonequilibrium charge carriers. The ratio of the contributions of tunneling and thermal escape is determined by the degree of isolation of quantum dots. A theoretical model is constructed that describes the effect of the dynamics of carrier transport on the emergence and decay of the slow component of photoluminescence.
Liu, Yanlan; Ai, Kelong; Yuan, Qinghai; Lu, Lehui
2011-02-01
We report here the development of Gd-doped ZnO quantum dots (QDs) as dual modal fluorescence and magnetic resonance imaging nanoprobes. They are fabricated in a simple, versatile and environmentally friendly method, not only decreasing the difficulty and complexity, but also avoiding the increase of particle's size brought about by silica coating procedure in the synthesis of nanoprobes reported previously. These nanoprobes, with exceptionally small size and enhanced fluorescence resulting from the Gd doping, can label successfully the HeLa cells in short time and present no evidence of toxicity or adverse affect on cell growth even at the concentration up to 1 mm. These results show that such nanoprobes have low toxicity, especially in comparison with the traditional PEGylated CdSe/ZnS or CdSe/CdS QDs. In MRI studies, they exert strong positive contrast effect with a large longitudinal relaxivity (r(1)) of water proton of 16 mm(-1) s(-1). Their capability of imaging HeLa cells with MRI implies that they have great potential as MRI contrast agents. Combining the high sensitivity of fluorescence imaging with high spatial resolution of MRI, We expect that the as-prepared Gd-doped Zno QDs can provide a better reliability of the collected data and find promising applications in biological, medical and other fields. Copyright © 2010 Elsevier Ltd. All rights reserved.
Quantum effect enhanced magnetism of C-doped phosphorene nanoribbons: first-principles calculations.
Cai, Xiaolin; Niu, Chunyao; He, Yuan-Yao; Wang, Jianjun; Zhu, Zhili; Zhang, Liwei; Jia, Yu
2017-10-25
Manipulating magnetism of low-dimensional materials is of great importance for their practical applications. Here, using first-principles calculations, we report a systematic investigation of the magnetic properties of C-doped H saturated zigzag phosphorene nanoribbons (H-ZPNRs), which are rather different from those of 2D periodic systems due to the quantum size effect. First of all, we observed a greatly enhanced magnetic moment locating mainly on the C atom and also slightly on its surrounding P atoms. Our results also indicated a strong dependence of the magnetic moment of the C atom on its location, which decays from the edge to the center site of the nanoribbons with an odd-even oscillating behavior originating from Friedel oscillation in low-dimensional materials. As for the C atom on a specific location, its magnetic moment decreases gradually with increasing width of H-ZPNRs, degenerating to the 2D case. What is more, we found that both the magnitude and the oscillating behavior of the magnetic moment on the C atom can be tuned by the edge saturation atoms. In addition, the case of two C atoms co-doping H-ZPNRs was also studied, showing non-magnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM) states depending on the locations of the two C atoms. Our findings suggest a plausible route for manipulating magnetism of the sp element doped H-ZPNRs, which are expected to have potential applications in spintronics.
Medina-Sánchez, Mariana; Miserere, Sandrine; Cadevall, Miquell; Merkoçi, Arben
2016-02-01
In this study, we propose an electrochemical immunoassay into a disposable microfluidic platform, using quantum dots (QDs) as labels and their enhanced detection using bismuth as an alternative to mercury electrodes. CdSe@ZnS QDs were used to tag human IgG as a model protein and detected through highly sensitive stripping voltammetry of the dissolved metallic component (cadmium in our case). The modification of the screen printed carbon electrodes (SPCEs) was done by a simple electrodeposition of bismuth that was previously mixed with the sample containing QDs. A magneto-immunosandwich assay was performed using a micromixer. A magnet placed at its outlet in order to capture the magnetic beads used as solid support for the immunoassay. SPCEs were integrated at the end of the channel as detector. Different parameters such as bismuth concentration, flow rate, and incubation times, were optimized. The LOD for HIgG in presence of bismuth was 3.5 ng/mL with a RSD of 13.2%. This LOD was about 3.3-fold lower than the one obtained without bismuth. Furthermore, the sensitivity of the system was increased 100-fold respect to experiments carried out with classical screen-printed electrodes, both in presence of bismuth. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
An enhanced high-speed multi-digit BCD adder using quantum-dot cellular automata
Ajitha, D.; Ramanaiah, K. V.; Sumalatha, V.
2017-02-01
The advent of development of high-performance, low-power digital circuits is achieved by a suitable emerging nanodevice called quantum-dot cellular automata (QCA). Even though many efficient arithmetic circuits were designed using QCA, there is still a challenge to implement high-speed circuits in an optimized manner. Among these circuits, one of the essential structures is a parallel multi-digit decimal adder unit with significant speed which is very attractive for future environments. To achieve high speed, a new correction logic formulation method is proposed for single and multi-digit BCD adder. The proposed enhanced single-digit BCD adder (ESDBA) is 26% faster than the carry flow adder (CFA)-based BCD adder. The multi-digit operations are also performed using the proposed ESDBA, which is cascaded innovatively. The enhanced multi-digit BCD adder (EMDBA) performs two 4-digit and two 8-digit BCD addition 50% faster than the CFA-based BCD adder with the nominal overhead of the area. The EMDBA performs two 4-digit BCD addition 24% faster with 23% decrease in the area, similarly for 8-digit operation the EMDBA achieves 36% increase in speed with 21% less area compared to the existing carry look ahead (CLA)-based BCD adder design. The proposed multi-digit adder produces significantly less delay of (N -1) + 3.5 clock cycles compared to the N* One digit BCD adder delay required by the conventional BCD adder method. It is observed that as per our knowledge this is the first innovative proposal for multi-digit BCD addition using QCA.
Enhancement and sign change of magnetic correlations in a driven quantum many-body system
Görg, Frederik; Messer, Michael; Sandholzer, Kilian; Jotzu, Gregor; Desbuquois, Rémi; Esslinger, Tilman
2018-01-01
Periodic driving can be used to control the properties of a many-body state coherently and to realize phases that are not accessible in static systems. For example, exposing materials to intense laser pulses makes it possible to induce metal–insulator transitions, to control magnetic order and to generate transient superconducting behaviour well above the static transition temperature. However, pinning down the mechanisms underlying these phenomena is often difficult because the response of a material to irradiation is governed by complex, many-body dynamics. For static systems, extensive calculations have been performed to explain phenomena such as high-temperature superconductivity. Theoretical analyses of driven many-body Hamiltonians are more challenging, but approaches have now been developed, motivated by recent observations. Here we report an experimental quantum simulation in a periodically modulated hexagonal lattice and show that antiferromagnetic correlations in a fermionic many-body system can be reduced, enhanced or even switched to ferromagnetic correlations (sign reversal). We demonstrate that the description of the many-body system using an effective Floquet–Hamiltonian with a renormalized tunnelling energy remains valid in the high-frequency regime by comparing the results to measurements in an equivalent static lattice. For near-resonant driving, the enhancement and sign reversal of correlations is explained by a microscopic model of the system in which the particle tunnelling and magnetic exchange energies can be controlled independently. In combination with the observed sufficiently long lifetimes of the correlations in this system, periodic driving thus provides an alternative way of investigating unconventional pairing in strongly correlated systems experimentally.
Ju, Jian; Liu, Wei; Chen, Keren; Perlaki, Clint Michael; Feng, Chunhua; Liu, Quan
2017-02-01
In this work, we report a novel substrate for surface enhanced Raman spectroscopy (SERS) composed of silver nanoparticles protected by small nitrogen-doped Graphene Quantum Dots, i.e. Ag NPs-N-GQDs, synthesized under mild experimental conditions, which can preserve the SERS performance in normal indoor environment for up to 30 days. The field emission scanning electronic microscope (FESEM) images confirm that the N-GQDs play a significant role in the control of metallic nanoparticles morphology. The X-ray photoelectron spectroscopy (XPS) result clearly indicates the N-GQDs was successfully immobilized on the surface of silver nanoparticles (Ag NPs). Ag NPs-N-GQDs demonstrated Raman enhancement stronger than pure Ag NPs likely due to an increase in the number of the "hotspots" formed by coupled nanostructures. N-GQD protected Ag NPs were evaluated in SERS measurements of R6G when they were made fresh and have been stored in normal indoors condition for up to 30 days. Then Ag NPs-N-GQDs were used as a SERS substrate for glucose detection. The linearity range of glucose was found to be ranged from 1 μM to 1 M with a detection limit of 0.1 μM in glucose solutions. It was also applied successfully for glucose detection in rat blood samples. The present study demonstrates that the novel Ag NPs-N-GQDs nanostructure has great potential to be used as a cost effective sustained SERS substrate, which can be extremely useful in the wide adoption of SERS based sensors.
DEFF Research Database (Denmark)
Nikolic, Branislav K.; Saha, Kamal K.; Markussen, Troels
2012-01-01
We overview the nonequilibrium Green function combined with density functional theory (NEGF-DFT) approach to modeling of independent electronic and phononic quantum transport in nanoscale thermoelectrics with examples focused on a new class of devices where a single organic molecule is attached...... to two metallic zigzag graphene nanoribbons (ZGNRs) via highly transparent contacts. Such contacts make possible injection of evanescent wavefunctions from the ZGNR electrodes, so that their overlap within the molecular region generates a peak in the electronic transmission around the Fermi energy...... show how the often employed Brenner empirical interatomic potential for hydrocarbon systems fails to describe phonon transport in our single-molecule nanojunctions when contrasted with first-principles results obtained via NEGF-DFT methodology....
Anghel, S.; Passmann, F.; Singh, A.; Ruppert, C.; Poshakinskiy, A. V.; Tarasenko, S. A.; Moore, J. N.; Yusa, G.; Mano, T.; Noda, T.; Li, X.; Bristow, A. D.; Betz, M.
2018-03-01
Electron spin transport and dynamics are investigated in a single, high-mobility, modulation-doped, GaAs quantum well using ultrafast two-color Kerr-rotation microspectroscopy, supported by qualitative kinetic theory simulations of spin diffusion and transport. Evolution of the spins is governed by the Dresselhaus bulk and Rashba structural inversion asymmetries, which manifest as an effective magnetic field that can be extracted directly from the experimental coherent spin precession. A spin-precession length λSOI is defined as one complete precession in the effective magnetic field. It is observed that application of (i) an out-of-plane electric field changes the spin decay time and λSOI through the Rashba component of the spin-orbit coupling, (ii) an in-plane magnetic field allows for extraction of the Dresselhaus and Rashba parameters, and (iii) an in-plane electric field markedly modifies both the λSOI and diffusion coefficient.
Anti-bias voltage electron-Kondo transport in a quantum dot device driven by a graphene sheet
Chen, Xiongwen; Shi, Zhengang; Zhang, Shunru; Song, Kehui; Zhou, Guanghui
2015-01-01
We theoretically investigate the manipulation of electron-Kondo transport through a single-quantum dot (QD) two-electrode device by introducing a side-coupled graphene sheet. It is shown that with increase of coupling strength between the QD and the zero-potential graphene sheet, the anti-bias voltage capability of the QD-electrode Kondo resonance is improved obviously. This causes a high-conductance QD-electrode channel to be opened up for electron transport within a wide bias voltage range. Moreover, the conductance/current of the Kondo channel can be accurately controlled by adjusting the potential of the graphene sheet. These results may be useful for the observation of nonequilibrium Kondo effect and the design of high-conductance control device.
Avila, José; Chen, Chaoyu; Arango, Yulieth C.; Huang, Liubing; Grützmacher, Detlev; Lüth, Hans; Lu, J. Grace; Schäpers, Thomas; Asensio, Maria C.
2017-06-01
Using high-resolution Nano-Angle Resolved Photoemission Spectroscopy (Nano-ARPES), we have determined the electronic structure of the surface and bulk states of topological insulator Sb2Te3 nanowires, which have been also characterized by magnetoresistance measurements. The observed Aharonov-Bohm-type oscillations could be unambiguously related to the transport by topological protected surface states directly recorded by photoemission. We have measured Nano-ARPES on individual nanowires of a few nanometers wide to provide direct evidence of the existence of the nontrivial topological surface states, as well as their doping. Our findings are consistent with theoretical predictions and confirm that the surface states of intrinsically doped unidimensional topological insulator nanowires are responsible for the quantum transport.
Eisner, Flurin
2018-04-25
We report the development of a solution‐processed In2O3/ZnO heterojunction electron transport layer (ETL) and its application in high efficiency organic bulk‐heterojunction (BHJ) and inorganic colloidal quantum dot (CQD) solar cells. Study of the electrical properties of this low‐dimensional oxide heterostructure via field‐effect measurements reveals that electron transport along the heterointerface is enhanced by more than a tenfold when compared to the individual single‐layer oxides. Use of the heterojunction as the ETL in organic BHJ photovoltaics is found to consistently improve the cell\\'s performance due to the smoothening of the ZnO surface, increased electron mobility and a noticeable reduction in the cathode\\'s work function, leading to a decrease in the cells’ series resistance and a higher fill factor (FF). Specifically, non‐fullerene based organic BHJ solar cells based on In2O3/ZnO ETLs exhibit very high power conversion efficiencies (PCE) of up to 12.8%, and high FFs of over 70%. The bilayer ETL concept is further extended to inorganic lead‐sulphide CQD solar cells. Resulting devices exhibit excellent performance with a maximum PCE of 8.2% and a FF of 56.8%. The present results highlight the potential of multilayer oxides as novel ETL systems and lay the foundation for future developments.
Bishop, Nathaniel; Young, Ralph; Borras Pinilla, Carlos; Stalford, Harold; Nielsen, Erik; Muller, Richard; Rahman, Rajib; Tracy, Lisa; Wendt, Joel; Lilly, Michael; Carroll, Malcolm
2012-02-01
We discuss trade-offs of different double quantum dot and charge sensor lay-outs using computer assisted design (CAD). We use primarily a semi-classical model, augmented with a self-consistent configuration interaction method. Although CAD for quantum dots is difficult due to uncontrolled factors (e.g., disorder), different ideal designs can still be compared. Comparisons of simulation and measured dot characteristics, such as capacitance, show that CAD can agree well with experiment for relevant cases. CAD results comparing several different designs will be discussed including a comparison to measurement results from the same designs. Trade-offs between poly-silicon and metal gate lay-outs will also be discussed. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE, Office of Basic Energy Sciences user facility. The work was supported by the Sandia National Laboratories Directed Research and Development Program. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Todorov, Yanko; Sagnes, Isabelle; Abram, Izo; Minot, Christophe
2007-11-30
Quantum cascade devices processed into double metal cavities with subwavelength thickness and a grating on top are studied at terahertz frequencies. The power extracted from the devices as a function of the device thickness and the grating period is analyzed owing to electrodynamical modeling of dipole emission based on a modal method in multilayer systems. The experimental data thus reveal a strong Purcell enhancement, with Purcell factors up to approximately 50.
2003-09-09
Mr. Guerrero's testimony examines (1) challenges in securing the nation's transportation system; (2) actions transportation operators, as well as state and local governments, have taken since September 11 to enhance security; (3) the federal role in ...
Wang, Xiaojun; Liu, Yongchang; Wang, Yijing; Jiao, Lifang
2016-09-01
The design of sodium ion batteries is proposed based on the use of flexible membrane composed of ultrasmall transition metal oxides. In this paper, the preparation of CuO quantum dots (≈2 nm) delicately embedded in carbon nanofibers (denoted as 2-CuO@C) with a thin film via a feasible electrospinning method is reported. The CuO content can be controlled by altering the synthetic conditions and is optimized to 54 wt%. As binder-free anode for sodium ion batteries, 2-CuO@C delivers an initial reversible capacity of 528 mA h g -1 at the current density of 100 mA g -1 , an exceptional rate capability of 250 mA h g -1 at 5000 mA g -1 , and an ultra-stable capacity of 401 mA h g -1 after 500 cycles at 500 mA g -1 . The enhancement of electrochemical performance is attributed to the unique structure of 2-CuO@C, which offers a variety of advantages: highly conductive carbon matrix suppressing agglomeration of CuO grains, interconnected nanofibers ensuring short transport length for electrons, well-dispersed CuO quantum dots leading to highly utilization rate, and good mechanical properties resulting in strong electrode integrity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Synthesis, characterization, Raman, and surface enhanced Raman studies of semiconductor quantum dots
Pan, Yi
The major contributions and discoveries of the dissertation include: (1) Homogeneous nucleation processes for the formation of nanocrystals can occur at low temperature and do not need to proceed at high temperature to overcome a high energy barrier. Monodisperse PbS quantum dots (QDs) obtained with nucleation and growth at 45°C support this finding. (2) Monodisperse single elemental Se QDs can be produced by simple solution crystallization from TDE (1-tetradecene) or ODE (1-octadecene). (3) TDE is a better non-coordinating solvent compare to ODE. STDE (S dissolved in TDE) and SeTDE (Se dissolved in TDE) are stable reagents with long storage time. They can be used as universal precursors for S-containing and Se-containing QDs. (4) QDs synthesis can be carried out at low temperature and relatively short reaction time using the simple, non-injection, one-pot synthetic method. (5) The one-pot method can be extended for the synthesis of QDs and graphene oxide nanocomposites and metal and graphene oxide nanocomposites. (6) PbCl2-OLA (oleylamine) is a universal system for the synthesis of Pb-chaclogenides QDs. (7) Surface enhanced Raman spectroscopy (SERS) is used to probe both size and wave length dependent quantum confinement effects (QCEs) of PbS QDs. (8) Raman spectroscopy is a powerful tool to elucidate crystal structure of Se nanoclusters with size of 1--2 nm. Semiconductor QDs have attracted considerable attention due to their potential for energy-efficient materials in optoelectronic and solar cell applications. When the radius of a QD is decreased to that of the exciton Bohr radius, the valence and conduction bands are known to split into narrower bands due to QCEs. QCEs are both size and wave length dependent. We have developed, synthesized and characterized a series of Pb-chaclogenide QDs, which all the sizes of the QDs are monodisperse and smaller than their respective exciton Bohr radius, to study the QCEs of these QDs. SERS is used as a crucial tool to
ZnSe passivation layer for the efficiency enhancement of CuInS2 quantum dots sensitized solar cells
International Nuclear Information System (INIS)
Peng, Zhuoyin; Liu, Yueli; Zhao, Yinghan; Chen, Keqiang; Cheng, Yuqing; Kovalev, Valery; Chen, Wen
2014-01-01
Highlights: • ZnSe is employed as passivation layer in CuInS 2 quantum dots sensitized solar cells. • Slight red-shift has been occurred in UV–vis absorption spectra with ZnSe coating. • CuInS 2 based solar cells coated by ZnSe have better efficiency than that of ZnS. • Higher rate of charge transport can be produced after coating with ZnSe. -- Abstract: The effect of ZnSe passivation layer is investigated in the CuInS 2 quantum dot sensitized solar cells, which is used to improve the photovoltaic performance. The CuInS 2 quantum dot sensitized TiO 2 photo-anodes are prepared by assembly linking technique, and then deposited by the ZnSe passivation layer using the successive ionic layer absorption and reaction technique. The optical absorption edge and photoluminescence peak have slightly red-shifted after the passivation layer coating. Under solar light illumination, the ZnSe passivation layer based CuInS 2 quantum dot sensitized solar cells have the higher photovoltaic efficiency of 0.95% and incident photon conversion efficiency response than that of pure CuInS 2 based solar cells and ZnS passivation layer based solar cells, as the electron injection rate becomes faster after coating with ZnSe passivation layer
Shafiq, Natis
Energy transfer (ET) based sensitization of silicon (Si) using proximal nanocrystal quantum dots (NQDs) has been studied extensively in recent years as a means to develop thin and flexible Si based solar cells. The driving force for this research activity is a reduction in materials cost. To date, the main method for determining the role of ET in sensitizing Si has been optical spectroscopic studies. The quantitative contribution from two modes of ET (namely, nonradiative and radiative) has been reported using time-resolved photoluminescence (TRPL) spectroscopy coupled with extensive theoretical modelling. Thus, optical techniques have established the potential for utilizing ET based sensitization of Si as a feasible way to develop novel NQD-Si hybrid solar cells. However, the ultimate measure of the efficiency of ET-based mechanisms is the generation of electron-hole pairs by the impinging photons. It is therefore important to perform electrical measurements. However, only a couple of studies have attempted electrical quantification of ET modes. A few studies have focused on photocurrent measurements, without considering industrially relevant photovoltaic (PV) systems. Therefore, there is a need to develop a systematic approach for the electrical quantification of ET-generated charges and to help engineer new PV architectures optimized for harnessing the full advantages of ET mechanisms. Within this context, the work presented in this dissertation aims to develop an experimental testing protocol that can be applied to different PV structures for quantifying ET contributions from electrical measurements. We fabricated bulk Si solar cells (SCs) as a test structure and utilized CdSe/ZnS NQDs for ET based sensitization. The NQD-bulk Si hybrid devices showed ˜30% PV enhancement after NQD deposition. We measured external quantum efficiency (EQE) of these devices to quantify ET-generated charges. Reflectance measurements were also performed to decouple contributions of
International Nuclear Information System (INIS)
Zhang Kejie; Liu Xiaoheng
2011-01-01
Well-dispersed carbon-coated CdS (CdS-C) quantum dots were successfully prepared via the improved pyrolysis of bis(1-dodecanethiol)-cadmium(II) under nitrogen atmosphere. This simple method effectively solved the sintered problem resulted from conventional pyrolysis process. The experimental results indicated that most of the as-prepared nanoparticles displayed well-defined core-shell structures. The CdS cores with diameter of ∼5 nm exhibited hexagonal crystal phase, the carbon shells with thickness of ∼2 nm acted as a good dispersion medium to prevent CdS particles from aggregation, and together with CdS effectively formed a monodisperse CdS-Carbon nanocomposite. This composite presented a remarkable fluorescence enhancement effect, which indicated that the prepared nanoparticles might be a promising photoresponsive material or biosensor. This improved pyrolysis method might also offer a facile way to prepare other carbon-coated semiconductor nanostructures. - Graphical abstract: We demonstrated a facile approach to synthesize well-dispersed carbon-coated CdS quantum dots. The as-prepared nanoparticles presented remarkable fluorescence enhancement effect. Highlights: → Carbon-coated CdS quantum dots were synthesized by an one-step pyrolysis method. → Well-dispersed CdS-carbon nanoparticles were obtained by an acid treatment process. → As-prepared nanoparticles presented remarkable fluorescence enhancement effect.
Inkjet-Printed Quantum Dot Light-Emitting Diodes with an Air-Stable Hole Transport Material.
Xing, Zhenhua; Zhuang, Jinyong; Wei, Changting; Zhang, Dongyu; Xie, Zhongzhi; Xu, Xiaoping; Ji, Shunjun; Tang, Jianxin; Su, Wenming; Cui, Zheng
2017-05-17
High-efficiency quantum dot light-emitting diodes (QLEDs) were fabricated using inkjet printing with a novel cross-linkable hole transport material N,N'-(9,9'-spirobi[fluorene]-2,7-diylbis[4,1-phenylene])bis(N-phenyl-4'-vinyl-[1,1'-biphenyl]-4-amine) (SDTF). The cross-linked SDTF film has excellent solvent resistance, high thermal stability, and the highest occupied molecular orbital (HOMO) level of -5.54 eV. The inkjet-printed SDTF film is very smooth and uniform, with roughness as low as 0.37 nm, which is comparable with that of the spin-coated film (0.28 nm). The SDTF films stayed stable without any pinhole or grain even after 2 months in air. All-solution-processed QLEDs were fabricated; the maximum external quantum efficiency of 5.54% was achieved with the inkjet-printed SDTF in air, which is comparable to that of the spin-coated SDTF in a glove box (5.33%). Electrical stabilities of both spin-coated and inkjet-printed SDTF at the device level were also investigated and both showed a similar lifetime. The study demonstrated that SDTF is very promising as a printable hole transport material for making QLEDs using inkjet printing.
Enhanced Photon Extraction from a Nanowire Quantum Dot Using a Bottom-Up Photonic Shell
DEFF Research Database (Denmark)
Jeannin, Mathieu; Cremel, Thibault; Häyrynen, Teppo
2017-01-01
Semiconductor nanowires offer the possibility to grow high-quality quantum-dot heterostructures, and, in particular, CdSe quantum dots inserted in ZnSe nanowires have demonstrated the ability to emit single photons up to room temperature. In this paper, we demonstrate a bottom-up approach...
Enhanced trans-Himalaya pollution transport to the Tibetan Plateau by cut-off low systems
Zhang, Ruixiong; Wang, Yuhang; He, Qiusheng; Chen, Laiguo; Zhang, Yuzhong; Qu, Hang; Smeltzer, Charles; Li, Jianfeng; Alvarado, Leonardo M. A.; Vrekoussis, Mihalis; Richter, Andreas; Wittrock, Folkard; Burrows, John P.
2017-02-01
Long-range transport followed by deposition of black carbon on glaciers of Tibet is one of the key issues of climate research as it induces changes on radiative forcing and subsequently impacting the melting of glaciers. The transport mechanism, however, is not well understood. In this study, we use short-lived reactive aromatics as proxies to diagnose transport of pollutants to Tibet. In situ observations of short-lived reactive aromatics across the Tibetan Plateau are analyzed using a regional chemistry and transport model. The model performance using the current emission inventories over the region is poor due to problems in the inventories and model transport. Top-down emissions constrained by satellite observations of glyoxal are a factor of 2-6 higher than the a priori emissions over the industrialized Indo-Gangetic Plain. Using the top-down emissions, agreement between model simulations and surface observations of aromatics improves. We find enhancements of reactive aromatics over Tibet by a factor of 6 on average due to rapid transport from India and nearby regions during the presence of a high-altitude cut-off low system. Our results suggest that the cut-off low system is a major pathway for long-range transport of pollutants such as black carbon. The modeling analysis reveals that even the state-of-the-science high-resolution reanalysis cannot simulate this cut-off low system accurately, which probably explains in part the underestimation of black carbon deposition over Tibet in previous modeling studies. Another model deficiency of underestimating pollution transport from the south is due to the complexity of terrain, leading to enhanced transport. It is therefore challenging for coarse-resolution global climate models to properly represent the effects of long-range transport of pollutants on the Tibetan environment and the subsequent consequence for regional climate forcing.
Atzori, Matteo; Morra, Elena; Tesi, Lorenzo; Albino, Andrea; Chiesa, Mario; Sorace, Lorenzo; Sessoli, Roberta
2016-09-07
In the search for long-lived quantum coherence in spin systems, vanadium(IV) complexes have shown record phase memory times among molecular systems. When nuclear spin-free ligands are employed, vanadium(IV) complexes can show at low temperature sufficiently long quantum coherence times, Tm, to perform quantum operations, but their use in real devices operating at room temperature is still hampered by the rapid decrease of T1 caused by the efficient spin-phonon coupling. In this work we have investigated the effect of different coordination environments on the magnetization dynamics and the quantum coherence of two vanadium(IV)-based potential molecular spin qubits in the solid state by introducing a unique structural difference, i.e., an oxovanadium(IV) in a square pyramidal versus a vanadium(IV) in an octahedral environment featuring the same coordinating ligand, namely, the 1,3-dithiole-2-thione-4,5-dithiolate. This investigation, performed by a combined approach of alternate current (ac) susceptibility measurements and continuous wave (CW) and pulsed electron paramagnetic resonance (EPR) spectroscopies revealed that the effectiveness of the vanadyl moiety in enhancing quantum coherence up to room temperature is related to a less effective mechanism of spin-lattice relaxation that can be quantitatively evaluated by the exponent n (ca. 3) of the temperature dependence of the relaxation rate. A more rapid collapse is observed for the non-oxo counterpart (n = 4) hampering the observation of quantum coherence at room temperature. Record coherence time at room temperature (1.04 μs) and Rabi oscillations are also observed for the vanadyl derivative in a very high concentrated material (5 ± 1%) as a result of the additional benefit provided by the use of a nuclear spin-free ligand.
Li, Guijun; Zhu, Changhua; Gan, Lijun; Ng, Denny; Xia, Kai
2015-03-01
We used auxin-signalling mutants, auxin transport mutants, and auxin-related marker lines to show that exogenously applied GA enhances auxin-induced root inhibition by affecting auxin signalling and transport. Variation in root elongation is valuable when studying the interactions of phytohormones. Auxins influence the biosynthesis and signalling of gibberellins (GAs), but the influence of GAs on auxins in root elongation is poorly understood. This study was conducted to investigate the effect of GA3 on Arabidopsis root elongation in the presence of auxin. Root elongation was inhibited in roots treated with both IAA and GA3, compared to IAA alone, and the effect was dose dependent. Further experiments showed that GA3 could modulate auxin signalling based on root elongation in auxin-signalling mutants and the expression of auxin-responsive reporters. The GA3-enhanced inhibition of root elongation observed in the wild type was not found in the auxin-signalling mutants tir1-1 and axr1-3. GA3 increased DR5::GUS expression in the root meristem and elongation zones, and IAA2::GUS in the columella. The DR5rev::GFP signal was enhanced in columella cells of the root caps and in the elongation zone in GA3-treated seedling roots. A reduction was observed in the stele of PAC-treated roots. We also examined the effect of GA3 on auxin transport. The enhanced responsiveness caused by GA3 was not observed in the auxin influx mutant aux1-7 or the efflux mutant eir1-1. Additional molecular data demonstrated that GA3 could promote auxin transport via AUX1 and PIN proteins. However, GA3-induced PIN gene expression did not fully explain GA-enhanced PIN protein accumulation. These results suggest that GA3 is involved in auxin-mediated primary root elongation by modulating auxin signalling and transport, and thus enhances root responsiveness to exogenous IAA.
DEFF Research Database (Denmark)
Broe, Jacob; Keller, Ole
2002-01-01
It is predicted that the Goos-Hänchen effect can be resonantly enhanced by placing a metallic quantum well (ultrathin film) at the dielectric-vacuum (air) interface. We study the enhancement of the phenomenon, as it appears in frustrated total internal reflection with p-polarized light, both...... by depositing quantum wells on the glass-vacuum interfaces to obtain a better spatial photon localization....
Energy Technology Data Exchange (ETDEWEB)
Guzmán, Álvaro, E-mail: guzman@die.upm.es; Yamamoto, Kenji; Ulloa, J. M.; Hierro, Adrian [Instituto de Sistemas Optoelectrónicos y Microtecnología y Dept. Ingeniería Electrónica, Universidad Politécnica de Madrid, ETSI de Telecomunicación, Avda. Complutense 30, 28040 Madrid (Spain); Llorens, J. M. [IMM-Instituto de Microelectrónica de Madrid (CNM-CSIC), Isaac Newton 8, PTM, E-28760 Tres Cantos, Madrid (Spain)
2015-07-06
InAs/GaAs{sub 1−x}Sb{sub x} Quantum Dot (QD) infrared photodetectors are analyzed by photocurrent spectroscopy. We observe that the integrated responsivity of the devices is improved with the increasing Sb mole fraction in the capping layer, up to 4.2 times for x = 17%. Since the QD layers are not vertically aligned, the vertical transport of the carriers photogenerated within the QDs takes place mainly through the bulk material and the wetting layer of the additional QD regions. The lower thickness of the wetting layer for high Sb contents results in a reduced capture probability of the photocarriers, thus increasing the photoconductive gain and hence, the responsivity of the device. The growth of not vertically aligned consecutive QD layers with a thinner wetting layer opens a possibility to improve the performance of quantum dot infrared photodetectors.
Wade, Jennifer S; Desai, Tejal A
2014-08-01
Large molecular weight drug delivery to the posterior eye is challenging due to cellular barriers that hinder drug transport. Understanding how to enhance transport across the retinal barrier is important for the design of new drug delivery systems. A novel mechanism to enhance drug transport is the use of geometric properties, which has not been extensively explored in the retina. Planar SU-8/Poly(ethyleneglycol)dimethacrylate microdevices were constructed using photolithography to deliver FITC dextran across an in vitro retinal model. The model consists of retinal pigment epithelial (RPE) cells grown to confluence on transwell inserts, which provides an environment to investigate the influence of geometry on paracellular and transcellular delivery of encapsulated large molecules. Planar microdevices enhanced transport of large molecular weight dextrans across different models of RPE in a size dependent fashion. Increased drug permeation across the RPE was observed with the addition of microdevices as compared to a traditional bolus of FITC dextran. This phenomena was initiated by a non-toxic interaction between the microdevices and the retinal tight junction proteins. Suggesting that increased drug transport occurs via a paracellular pathway. These experiments provide evidence to support the future use of planar unidirectional microdevices for delivery of biologics in ocular applications.
Zhang, Chenguang; Liu, Shaowen; Liu, Xingwei; Deng, Fei; Xiong, Yan; Tsai, Fang-Chang
2018-03-01
A photoelectric conversion efficiency (PCE) of 4.9% was obtained under 100 mW cm -2 illumination by quantum-dot-sensitized solar cells (QDSSCs) using a CdS/Mn : CdSe sensitizer. CdS quantum dots (QDs) were deposited on a TiO 2 mesoporous oxide film by successive ionic layer absorption and reaction. Mn 2+ doping into CdSe QDs is an innovative and simple method-chemical bath co-deposition, that is, mixing the Mn ion source with CdSe precursor solution for Mn : CdSe QD deposition. Compared with the CdS/CdSe sensitizer without Mn 2+ incorporation, the PCE was increased from 3.4% to 4.9%. The effects of Mn 2+ doping on the chemical, physical and photovoltaic properties of the QDSSCs were investigated by energy dispersive spectrometry, absorption spectroscopy, photocurrent density-voltage characteristics and electrochemical impedance spectroscopy. Mn-doped CdSe QDs in QDSSCs can obtain superior light absorption, faster electron transport and slower charge recombination than CdSe QDs.
Gu, Guiru; Vaillancourt, Jarrod; Lu, Xuejun
2014-10-20
In this paper, we analyze near-field vector components of a metallic circular disk array (MCDA) plasmonic optical antenna and their contribution to quantum dot infrared photodetector (QDIP) enhancement. The near-field vector components of the MCDA optical antenna and their distribution in the QD active region are simulated. The near-field overlap integral with the QD active region is calculated at different wavelengths and compared with the QDIP enhancement spectrum. The x-component (E(x)) of the near-field vector shows a larger intensity overlap integral and stronger correlation with the QDIP enhancement than E(z) and thus is determined to be the major near-field component to the QDIP enhancement.
Design and Implementation of Quantum Dot Enhanced Next Generation Photovoltaic Devices
Polly, Stephen Jade
Photovoltaics are an essential enabling technology providing power both where it would be impractical to deliver otherwise and where sustainably produced--and recently, economically competitive--energy is demanded. Significant effort has gone into increasing the efficiency of these devices since their initial development in the 1950s. The most dramatic enhancements have been from the judicious choice of material used for photon collection, with current state of the art (SOA) conversion efficiencies reaching 46%. Further improvements may be engineered through exploration of next-generation methodologies, such as the incorporation of quantum dots (QDs), to maximally exploit the solar spectrum and develop solar cells producing both large current densities and large voltages compared to current SOA. In this work, the electrical, optical, and mechanical properties of GaAs solar cells incorporating nanostructured InAs QDs, strain balanced with GaP, were studied. QDs allow for an increase in the current generation capabilities of the bulk GaAs semiconductor through absorption of sub-bandgap photons via bound states in the low-bandgap, low-dimensional material. QDs alter the recombination dynamics of charge carriers in the photovoltaic device, which typically led to an undesirable reduction in voltage of more than 200 mV. The addition of dopant, necessary to explore the effects of an intermediate band solar cell, showed a voltage recovery of 121 mV, with no positive or negative effects on sub-bandgap collection. Advanced characterization and data analysis techniques were developed, combining photoreflectance and temperature-dependent photoluminescence, to investigate the activation energy of bound states in the QD, which were shown to undesirably decrease by 34 meV to 40 meV with the addition of doping. Simulation of alternative structures that may help to increase this activation energy were performed using alternative strain balancing designs, and a general strain
Energy Technology Data Exchange (ETDEWEB)
Muthalif, Mohammed Panthakkal Abdul [Department of Polymer Science and Chemical Engineering, Pusan National University, Geumjeong-Ku, Jangjeong-Dong, Busan 609-735 (Korea, Republic of); Lee, Young-Seok [School of Electrical Engineering, Pusan National University, Geumjeong-Ku, Jangjeong-Dong, Busan 609-735 (Korea, Republic of); Sunesh, Chozhidakath Damodharan [Department of Polymer Science and Chemical Engineering, Pusan National University, Geumjeong-Ku, Jangjeong-Dong, Busan 609-735 (Korea, Republic of); Kim, Hee-Je [School of Electrical Engineering, Pusan National University, Geumjeong-Ku, Jangjeong-Dong, Busan 609-735 (Korea, Republic of); Choe, Youngson, E-mail: choe@pusan.ac.kr [Department of Polymer Science and Chemical Engineering, Pusan National University, Geumjeong-Ku, Jangjeong-Dong, Busan 609-735 (Korea, Republic of)
2017-02-28
Highlights: • Cu-doped CdS QDs were deposited on TiO{sub 2} by SILAR method. • Cu-doped CdS electrodes contributes reduction of charge recombination and longer electron lifetime. • A promising power conversion efficiency of 3% is obtained for the Cu-doped CdS Quantum dot sensitized solar cell. - Abstract: In this article, we have systematically probed the effect of Cu-doping in CdS quantum dots (QDs) to enhance the photovoltaic performance of the quantum dot-sensitized solar cells (QDSSCs). The Cu-doped CdS photoanodes were prepared by successive ionic layer adsorption and reaction (SILAR) method and the corresponding cell devices were fabricated using CuS counter electrodes with a polysulfide electrolyte. The photovoltaic performance results demonstrate that 3 mM Cu-doped CdS QDs based QDSSCs exhibit the efficiency (η) of 3% including J{sub SC} = 9.40 mA cm{sup −2}, V{sub OC} = 0.637 V, FF = 0.501, which are higher than those with bare CdS (η = 2.05%, J{sub SC} = 7.12 mA cm{sup −2}, V{sub OC} = 0.588 V, FF = 0.489). The structural, topographical and optical properties of the thin films have been studied with the help of X-ray diffraction pattern (XRD), atomic force microscopy (AFM) and UV–vis spectrophotometer. Electrochemical impedance spectroscopy (EIS) and open circuit voltage decay (OCVD) measurements indicate that Cu-dopant can inhibit the charge recombination at the photoanode/electrolyte interface and extend the lifetime of electrons. These results reveal that incorporation of copper metal in CdS QDs is a simple and effective method to improve the photovoltaic properties of QDSSCs.
DEFF Research Database (Denmark)
Durisic, Nela; Bachir, Alexia I; Kolin, David L
2007-01-01
Semiconductor nanocrystals or quantum dots (QDs) are becoming widely used as fluorescent labels for biological applications. Here we demonstrate that fluorescence fluctuation analysis of their diffusional mobility using temporal image correlation spectroscopy is highly susceptible to systematic...... application of the image correlation methods for measurement of the diffusion coefficient of glycosyl phosphatidylinositol-anchored proteins tagged with QDs as imaged on living fibroblasts Udgivelsesdato: 2007-Aug-15...
Dielectric coating and surface plasmon enhancement of multi-color quantum-well structures
DEFF Research Database (Denmark)
Fadil, Ahmed; Iida, Daisuke; Ou, Yiyu
We fabricate a multi-colored quantum-well structure as a prototype towards monolithic white light-emitting diodes, and modify the emission intensities of different colors by introducing dielectric and Ag nanoparticle coating.......We fabricate a multi-colored quantum-well structure as a prototype towards monolithic white light-emitting diodes, and modify the emission intensities of different colors by introducing dielectric and Ag nanoparticle coating....
Energy Technology Data Exchange (ETDEWEB)
Wing, Waylin J.; Sadeghi, Seyed M., E-mail: seyed.sadeghi@uah.edu; Gutha, Rithvik R.; Campbell, Quinn [Department of Physics, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States); Mao, Chuanbin [Department of Chemistry and Biochemistry, Stephenson Life Sciences Research Center, University of Oklahoma, Norman, Oklahoma 73019 (United States)
2015-09-28
We investigate the shape and size effects of gold metallic nanoparticles on the enhancement of exciton-plasmon coupling and emission of semiconductor quantum dots induced via the simultaneous impact of metal-oxide and plasmonic effects. This enhancement occurs when metallic nanoparticle arrays are separated from the quantum dots by a layered thin film consisting of a high index dielectric material (silicon) and aluminum oxide. Our results show that adding the aluminum oxide layer can increase the degree of polarization of quantum dot emission induced by metallic nanorods by nearly two times, when these nanorods have large aspect ratios. We show when the aspect ratio of these nanorods is reduced to half, the aluminum oxide loses its impact, leading to no improvement in the degree of polarization. These results suggest that a silicon/aluminum oxide layer can significantly enhance exciton-plasmon coupling when quantum dots are in the vicinity of metallic nanoantennas with high aspect ratios.
Hipp, J Aaron; Manteiga, Alicia; Burgess, Amanda; Stylianou, Abby; Pless, Robert
2016-01-01
Active transportation opportunities and infrastructure are an important component of a community's design, livability, and health. Features of the built environment influence active transportation, but objective study of the natural experiment effects of built environment improvements on active transportation is challenging. The purpose of this study was to develop and present a novel method of active transportation research using webcams and crowdsourcing, and to determine if crosswalk enhancement was associated with changes in active transportation rates, including across a variety of weather conditions. The 20,529 publicly available webcam images from two street intersections in Washington, DC, USA were used to examine the impact of an improved crosswalk on active transportation. A crowdsource, Amazon Mechanical Turk, annotated image data. Temperature data were collected from the National Oceanic and Atmospheric Administration, and precipitation data were annotated from images by trained research assistants. Summary analyses demonstrated slight, bi-directional differences in the percent of images with pedestrians and bicyclists captured before and after the enhancement of the crosswalks. Chi-square analyses revealed these changes were not significant. In general, pedestrian presence increased in images captured during moderate temperatures compared to images captured during hot or cold temperatures. Chi-square analyses indicated the crosswalk improvement may have encouraged walking and biking in uncomfortable outdoor conditions (P transportation. The use of webcams to collect active transportation data has applications for community policymakers, planners, and health professionals. Future research will work to validate this method in a variety of settings as well as across different built environment and community policy initiatives.
Single molecule charge transport : From a quantum mechanical to a classical description
Kocherzhenko, A.A.; Grozema, F.C.; Siebbeles, L.D.A.
2010-01-01
This paper explores charge transport at the single molecule level. The conductive properties of both small organic molecules and conjugated polymers (molecular wires) are considered. In particular, the reasons for the transition from fully coherent to incoherent charge transport and the approaches
A Green-function approach to transport phenomena in quantum pumps
Arrachea, Liliana
2005-01-01
We present a general treatment to study transport phenomena in systems described by tight-binding Hamiltonians coupled to reservoirs and with one or more time-periodic potentials. We apply this treatment to the study of transport phenomena in a double barrier structure with one and two harmonic potentials. Among other properties, we discuss the origin of the sign of the net current.
Mazzeo, Paolo P; Maini, Lucia; Petrolati, Alex; Fattori, Valeria; Shankland, Kenneth; Braga, Dario
2014-07-07
Organo-copper(i) halide complexes with a Cu4I4 cubane core and cyclic amines as ligands have been synthesized and their crystal structures have been defined. Their solid state photophysical properties have been measured and correlated with the crystal structure and packing. A unique and remarkably high luminescence quantum yield (76%) has been measured for one of the complexes having the cubane clusters arranged in a columnar structure and held together by N-HI hydrogen bonds. This high luminescence quantum yield is correlated with a slow radiationless deactivation rate of the excited state and suggests a rather strong enhancement of the cubane core rigidity bestowed by the hydrogen bond pattern. Some preliminary thin film deposition experiments show that these compounds could be considered to be good candidates for applications in electroluminescent devices because of their bright luminescence, low cost and relatively easy synthesis processes.
Energy Technology Data Exchange (ETDEWEB)
Ngai, J.H.; Segal, Y.; Su, D.; Zhu, Y.; Walker, F.J.; Ismail-Beigi, S.; Le Hur, K.; Ahn, C.H.
2010-06-21
Electron gases created by modulating the charge density near interfaces and surfaces of insulating SrTiO{sub 3} offer a wide range of tunable behavior. Here, we utilize the nonlinear dielectric response of SrTiO{sub 3} to electrostatically manipulate the spatial confinement of an electron gas relative to an interface, where scattering is enhanced. Magnetotransport measurements reveal that the electron gas can be tuned from weakly localized to classical transport regimes. This crossover in transport demonstrates that elastic scattering can be electrostatically controlled, providing another degree of tunability for electron gases in SrTiO{sub 3}.
Zygmanski, Piotr; Sajo, Erno
2016-01-01
We review radiation transport and clinical beam modelling for gold nanoparticle dose-enhanced radiotherapy using X-rays. We focus on the nanoscale radiation transport and its relation to macroscopic dosimetry for monoenergetic and clinical beams. Among other aspects, we discuss Monte Carlo and deterministic methods and their applications to predicting dose enhancement using various metrics.
Samant, Mugdha D; Jackson, Courtney M; Felix, Carina L; Jones, Anthony J; Goodrich, David W; Foster, Barbara A; Huss, Wendy J
2015-05-15
Multi-drug resistance (MDR)-ATP binding cassette (ABC) transporters, ABCB1, ABCC1, and ABCG2 participate in the efflux of steroid hormones, estrogens, and androgens, which regulate prostate development and differentiation. The role of MDR-ABC efflux transporters in prostate epithelial proliferation and differentiation remains unclear. We hypothesized that MDR-ABC transporters regulate prostate differentiation and epithelium regeneration. Prostate epithelial differentiation was studied using histology, sphere formation assay, and prostate regeneration induced by cycles of repeated androgen withdrawal and replacement. Embryonic deletion of Abcg2 resulted in a decreased number of luminal cells in the prostate and increased sphere formation efficiency, indicating an imbalance in the prostate epithelial differentiation pattern. Decreased luminal cell number in the Abcg2 null prostate implies reduced differentiation. Enhanced sphere formation efficiency in Abcg2 null prostate cells implies activation of the stem/progenitor cells. Prostate regeneration was associated with profound activation of the stem/progenitor cells, indicating the role of Abcg2 in maintaining stem/progenitor cell pool. Since embryonic deletion of Abcg2 may result in compensation by other ABC transporters, pharmacological inhibition of MDR-ABC efflux was performed. Pharmacological inhibition of MDR-ABC efflux enhanced prostate epithelial differentiation in sphere culture and during prostate regeneration. In conclusion, Abcg2 deletion leads to activation of the stem/progenitor cells and enhances differentiating divisions; and pharmacological inhibition of MDR-ABC efflux leads to epithelial differentiation. Our study demonstrates for the first time that MDR-ABC efflux transporter inhibition results in enhanced prostate epithelial cell differentiation.
Energy Technology Data Exchange (ETDEWEB)
Rogacheva, E. I.; Budnik, A. V.; Sipatov, A. Yu.; Nashchekina, O. N. [National Technical University “Kharkov Polytechnic Institute,” 21 Frunze St., Kharkov 61002 (Ukraine); Dresselhaus, M. S. [Department of Electrical Engineering and Computer Science and Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139 (United States)
2015-02-02
The dependences of the electrical conductivity, the Hall coefficient, and the Seebeck coefficient on the layer thickness d (d = 18−600 nm) of p-type topological insulator Bi{sub 2}Te{sub 3} thin films grown by thermal evaporation in vacuum on glass substrates were obtained at room temperature. In the thickness range of d = 18–100 nm, sustained oscillations with a substantial amplitude were revealed. The observed oscillations are well approximated by a harmonic function with a period Δd = (9.5 ± 0.5) nm. At d > 100 nm, the transport coefficients practically do not change as d is increased. The oscillations of the kinetic properties are attributed to the quantum size effects due to the hole confinement in the Bi{sub 2}Te{sub 3} quantum wells. The results of the theoretical calculations of Δd within the framework of a model of an infinitely deep potential well are in good agreement with the experimental results. It is suggested that the substantial amplitude of the oscillations and their sustained character as a function of d are connected with the topologically protected gapless surface states of Bi{sub 2}Te{sub 3} and are inherent to topological insulators.
Photogenerated carriers transport behaviors in L-cysteine capped ZnSe core-shell quantum dots
Shan, Qingsong; Li, Kuiying; Xue, Zhenjie; Lin, Yingying; Yin, Hua; Zhu, Ruiping
2016-02-01
The photoexcited carrier transport behavior of zinc selenide (ZnSe) quantum dots (QDs) with core-shell structure is studied because of their unique photoelectronic characteristics. The surface photovoltaic (SPV) properties of self-assembled ZnSe/ZnS/L-Cys core-shell QDs were probed via electric field induced surface photovoltage and transient photovoltage (TPV) measurements supplemented by Fourier transform infrared, laser Raman, absorption, and photoluminescence spectroscopies. The ZnSe QDs displayed p-type SPV characteristics with a broader stronger SPV response over the whole ultraviolet-to-near-infrared range compared with those of other core-shell QDs in the same group. The relationship between the SPV phase value of the QDs and external bias was revealed in their SPV phase spectrum. The wide transient photovoltage response region from 3.3 × 10-8 to 2 × 10-3 s was closely related to the long diffusion distance of photoexcited free charge carriers in the interfacial space-charge region of the QDs. The strong SPV response corresponding to the ZnSe core mainly originated from an obvious quantum tunneling effect in the QDs.
Photogenerated carriers transport behaviors in L-cysteine capped ZnSe core-shell quantum dots
Energy Technology Data Exchange (ETDEWEB)
Shan, Qingsong; Li, Kuiying, E-mail: kuiyingli@ysu.edu.cn; Lin, Yingying; Yin, Hua; Zhu, Ruiping [State Key Laboratory of Metastable Materials Manufacture Technology and Science, Yanshan University, Qinhuangdao 066004 (China); Xue, Zhenjie [Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)
2016-02-07
The photoexcited carrier transport behavior of zinc selenide (ZnSe) quantum dots (QDs) with core–shell structure is studied because of their unique photoelectronic characteristics. The surface photovoltaic (SPV) properties of self-assembled ZnSe/ZnS/L-Cys core–shell QDs were probed via electric field induced surface photovoltage and transient photovoltage (TPV) measurements supplemented by Fourier transform infrared, laser Raman, absorption, and photoluminescence spectroscopies. The ZnSe QDs displayed p-type SPV characteristics with a broader stronger SPV response over the whole ultraviolet-to-near-infrared range compared with those of other core–shell QDs in the same group. The relationship between the SPV phase value of the QDs and external bias was revealed in their SPV phase spectrum. The wide transient photovoltage response region from 3.3 × 10{sup −8} to 2 × 10{sup −3} s was closely related to the long diffusion distance of photoexcited free charge carriers in the interfacial space–charge region of the QDs. The strong SPV response corresponding to the ZnSe core mainly originated from an obvious quantum tunneling effect in the QDs.
Frequency and thermal effects on the enhancement of transdermal transport by sonophoresis.
Merino, Gustavo; Kalia, Yogeshvar N; Delgado-Charro, M Begoña; Potts, Russell O; Guy, Richard H
2003-02-14
The aims of this work were: (i) to examine the role of ultrasound (US) frequency and intensity on the transport of glucose and mannitol across porcine skin in vitro, (ii) to quantify the energy delivered to the skin during application of low-frequency sonophoresis, and (iii) to 'deconvolute' the thermal effect, induced by US application to the skin, to the enhanced permeability of the cutaneous barrier. Low- (20 kHz) and high-frequency (10 MHz) sonophoresis were first compared. Only low frequency US resulted in significantly increased permeation. Low-frequency, US-induced enhancement of mannitol transport was symmetric; that is, mannitol flux was the same when 'delivered' or 'extracted' from a donor solution (in both cases, the US probe was present on the surface side of the skin). Calorimetry was used to quantify the US energy delivered by the sonicator. Subsequently, the US-enhanced transdermal transport of mannitol, during which a significant (and US intensity-dependent) temperature increase occurred, was compared to that provoked, in the absence of sonophoresis, by a comparable thermal effect. Only 25% of this enhancement was attributable to the increased temperature induced by US. It follows that another mechanism, most probably cavitation, is principally responsible for the lowered skin barrier function observed.
Energy Technology Data Exchange (ETDEWEB)
Goodman, Samuel M.; Singh, Vivek [Department of Chemical and Biological Engineering, University of Colorado Boulder, 3415 Colorado Avenue, Boulder, Colorado 80303 (United States); Noh, Hyunwoo [Department of Chemical and Biological Engineering, University of Colorado Boulder, 3415 Colorado Avenue, Boulder, Colorado 80303 (United States); Materials Science and Engineering Program and Department of Nanoengineering, University of California, 9500 Gilman Drive, La Jolla, San Diego, California 92093 (United States); Cha, Jennifer N. [Department of Chemical and Biological Engineering, University of Colorado Boulder, 3415 Colorado Avenue, Boulder, Colorado 80303 (United States); Materials Science and Engineering Program and Department of Nanoengineering, University of California, 9500 Gilman Drive, La Jolla, San Diego, California 92093 (United States); Materials Science and Engineering, University of Colorado Boulder, 3415 Colorado Avenue, Boulder, Colorado 80303 (United States); Nagpal, Prashant, E-mail: pnagpal@colorado.edu [Department of Chemical and Biological Engineering, University of Colorado Boulder, 3415 Colorado Avenue, Boulder, Colorado 80303 (United States); Materials Science and Engineering, University of Colorado Boulder, 3415 Colorado Avenue, Boulder, Colorado 80303 (United States); BioFrontiers Institute, University of Colorado Boulder, 3415 Colorado Avenue, Boulder, Colorado 80303 (United States); Renewable and Sustainable Energy Institute, University of Colorado Boulder, 2445 Kittredge Loop, Boulder, Colorado 80309 (United States)
2015-02-23
Quantum dot (QD), or semiconductor nanocrystal, thin films are being explored for making solution-processable devices due to their size- and shape-tunable bandgap and discrete higher energy electronic states. While DNA has been extensively used for the self-assembly of nanocrystals, it has not been investigated for the simultaneous conduction of multiple energy charges or excitons via exciton shelves (ES) formed in QD-DNA nano-bioelectronic thin films. Here, we present studies on charge conduction through exciton shelves, which are formed via chemically coupled QDs and DNA, between electronic states of the QDs and the HOMO-LUMO levels in the complementary DNA nucleobases. While several challenges need to be addressed in optimizing the formation of devices using QD-DNA thin films, a higher charge collection efficiency for hot-carriers and our detailed investigations of charge transport mechanism in these thin films highlight their potential for applications in nano-bioelectronic devices and biological transducers.
Wu, Zhenhua; Luo, Kun; Yu, Jiahan; Wu, Xiaobo; Lin, Liangzhong
2018-02-01
Electron tunneling through a single magnetic barrier in a HgTe topological insulator has been theoretically investigated. We find that the perpendicular magnetic field would not lead to spin-flip of the edge states due to the conservation of the angular moment. By tuning the magnetic field and the Fermi energy, the edge channels can be transited from switch-on states to switch-off states and the current from unpolarized states can be filtered to fully spin polarized states. These features offer us an efficient way to control charge/spin transport in a HgTe/CdTe quantum well, and pave a way to construct the nanoelectronic devices utilizing the topological edge states.
Ghaderzadeh, A.; Rahbari, S. H. Ebrahimnazhad; Phirouznia, A.
2018-03-01
In this study, Rashba coupling induced Aharonov-Casher effect in a graphene based nano ring is investigated theoretically. The graphene based nano ring is considered as a central device connected to semi-infinite graphene nano ribbons. In the presence of the Rashba spin-orbit interaction, two armchair shaped edge nano ribbons are considered as semi-infinite leads. The non-equilibrium Green's function approach is utilized to obtain the quantum transport characteristics of the system. The relaxation and dephasing mechanisms within the self-consistent Born approximation is scrutinized. The Lopez-Sancho method is also applied to obtain the self-energy of the leads. We unveil that the non-equilibrium current of the system possesses measurable Aharonov-Casher oscillations with respect to the Rashba coupling strength. In addition, we have observed the same oscillations in dilute impurity regimes in which amplitude of the oscillations is shown to be suppressed as a result of the relaxations.
Pickering, Kenneth E.; Thompson, Anne M.; Dickerson, Russell R.
1989-01-01
Vertical profiles of net photochemical ozone production rates and total tropospheric column production rates were estimated using two models, a simple photochemical box model and a time-dependent one-dimensional transport/kinetics model. Photochemical production of ozone is found to dominate over destruction throughout the vertical extent of the troposphere over the central United States during typical summertime convective conditions. The column net production can be enhanced by the transport of the ozone precursors NO and NMHC from the boundary layer to the free troposphere by convective activity.
Enhanced Photon Extraction from a Nanowire Quantum Dot Using a Bottom-Up Photonic Shell
Jeannin, Mathieu; Cremel, Thibault; Häyrynen, Teppo; Gregersen, Niels; Bellet-Amalric, Edith; Nogues, Gilles; Kheng, Kuntheak
2017-11-01
Semiconductor nanowires offer the possibility to grow high-quality quantum-dot heterostructures, and, in particular, CdSe quantum dots inserted in ZnSe nanowires have demonstrated the ability to emit single photons up to room temperature. In this paper, we demonstrate a bottom-up approach to fabricate a photonic fiberlike structure around such nanowire quantum dots by depositing an oxide shell using atomic-layer deposition. Simulations suggest that the intensity collected in our NA =0.6 microscope objective can be increased by a factor 7 with respect to the bare nanowire case. Combining microphotoluminescence, decay time measurements, and numerical simulations, we obtain a fourfold increase in the collected photoluminescence from the quantum dot. We show that this improvement is due to an increase of the quantum-dot emission rate and a redirection of the emitted light. Our ex situ fabrication technique allows a precise and reproducible fabrication on a large scale. Its improved extraction efficiency is compared to state-of-the-art top-down devices.
Directory of Open Access Journals (Sweden)
Hao Yang
2017-03-01
Full Text Available A facile and effective growing strategy of graphite-like carbon nitride quantum dots (CNQDs modified on ZnO nanowire array composite electrodes has been successfully designed and prepared for the first time. The remarkable quantum enhanced properties were carefully studied by means of scanning electron microscope (SEM, transmission electron microscopy (TEM, X-ray photoelectron spectroscope (XPS, UV-vis diffuse reflectance, PEC performance, and photocatalytic hydrogen production, and the results were in good agreement. Fivefold enhanced photoelectrochemical performances of this novel hierarchical hetero-array prepared in this paper compared with pure ZnO nanowire arrays were obtained under UV-light. The effect was attributed to the remarkable charge separation between CNQDs and ZnO nanowire arrays. Additional investigations revealed that the particular structure of CNQDs/ZnO composites contributed to the separation of a photon-generation carrier and an enhanced photoelectric current. Moreover, the absorption edge of CNQD-modified ZnO nanowire arrays was slightly broadened, and the diameter was reduced as well. The photoelectrochemistry hydrogen evolution splitting water using simulated solar irradiation exhibited the foreground of a possible application of a mechanism of photoelectrochemistry hydrogen evolution over CNQDs/ZnO composite electrodes.
He, Yong
2017-06-23
We utilize the surface plasmon field of a metal nanoparticle (MNP) to show strain-mediated coupling in a quantum dot-mechanical resonator hybrid system including a quantum dot (QD) embedded within a conical nanowire (NW) and a MNP in the presence of an external field. Based on the numerical solutions of the master equation, we find that a slow oscillation, originating from the strain-mediated coupling between the QD and the NW, appears in the time evolution of the plasmon field enhancement. The results show that the period (about [Formula: see text]) of the slow oscillation is equal to that of the mechanical resonator of NW, which suggests that the time-resolved measurement of the plasmon field enhancement can be easily achieved based on the current experimental conditions. Its amplitude increases with the increasing strain-mediated coupling strength, and under certain conditions there is a linear relationship between them. The slow oscillation of the plasmon field enhancement provides valuable tools for measurements of the mechanical frequency and the strain-mediated coupling strength.
Tsai, Yu-Lin; Wang, Sheng-Wen; Huang, Jhih-Kai; Hsu, Lung-Hsing; Chiu, Ching-Hsueh; Lee, Po-Tsung; Yu, Peichen; Lin, Chien-Chung; Kuo, Hao-Chung
2015-11-30
This work demonstrates the enhanced power conversion efficiency (PCE) in InGaN/GaN multiple quantum well (MQWs) solar cells with gradually decreasing indium composition in quantum wells (GQWs) toward p-GaN as absorber. The GQW can improve the fill factor from 42% to 62% and enhance the short current density from 0.8 mA/cm2 to 0.92 mA/cm2, as compares to the typical MQW solar cells. As a result, the PCE is boosted from 0.63% to 1.11% under AM1.5G illumination. Based on simulation and experimental results, the enhanced PCE can be attributed to the improved carrier collection in GQW caused by the reduction of potential barriers and piezoelectric polarization induced fields near the p-GaN layer. The presented concept paves a way toward highly efficient InGaN-based solar cells and other GaN-related MQW devices.
He, Yong
2017-06-01
We utilize the surface plasmon field of a metal nanoparticle (MNP) to show strain-mediated coupling in a quantum dot-mechanical resonator hybrid system including a quantum dot (QD) embedded within a conical nanowire (NW) and a MNP in the presence of an external field. Based on the numerical solutions of the master equation, we find that a slow oscillation, originating from the strain-mediated coupling between the QD and the NW, appears in the time evolution of the plasmon field enhancement. The results show that the period (about 2 μ s) of the slow oscillation is equal to that of the mechanical resonator of NW, which suggests that the time-resolved measurement of the plasmon field enhancement can be easily achieved based on the current experimental conditions. Its amplitude increases with the increasing strain-mediated coupling strength, and under certain conditions there is a linear relationship between them. The slow oscillation of the plasmon field enhancement provides valuable tools for measurements of the mechanical frequency and the strain-mediated coupling strength.
Le Gouët, Jean-Louis; Moiseev, Sergey
2012-06-01
Interaction of quantum radiation with multi-particle ensembles has sparked off intense research efforts during the past decade. Emblematic of this field is the quantum memory scheme, where a quantum state of light is mapped onto an ensemble of atoms and then recovered in its original shape. While opening new access to the basics of light-atom interaction, quantum memory also appears as a key element for information processing applications, such as linear optics quantum computation and long-distance quantum communication via quantum repeaters. Not surprisingly, it is far from trivial to practically recover a stored quantum state of light and, although impressive progress has already been accomplished, researchers are still struggling to reach this ambitious objective. This special issue provides an account of the state-of-the-art in a fast-moving research area that makes physicists, engineers and chemists work together at the forefront of their discipline, involving quantum fields and atoms in different media, magnetic resonance techniques and material science. Various strategies have been considered to store and retrieve quantum light. The explored designs belong to three main—while still overlapping—classes. In architectures derived from photon echo, information is mapped over the spectral components of inhomogeneously broadened absorption bands, such as those encountered in rare earth ion doped crystals and atomic gases in external gradient magnetic field. Protocols based on electromagnetic induced transparency also rely on resonant excitation and are ideally suited to the homogeneous absorption lines offered by laser cooled atomic clouds or ion Coulomb crystals. Finally off-resonance approaches are illustrated by Faraday and Raman processes. Coupling with an optical cavity may enhance the storage process, even for negligibly small atom number. Multiple scattering is also proposed as a way to enlarge the quantum interaction distance of light with matter. The
Zhao, Kui
2016-07-13
We demonstrate that local and long range orders of poly(3-hexylthiophene) (P3HT) semicrystalline films can be synergistically improved by combining chemical functionalization of the dielectric surface with solution-state disentanglement and pre-aggregation of P3HT in a theta solvent, leading to a very significant enhancement of the field effect carrier mobility. The pre-aggregation and surface functionalization effects combine to enhance the carrier mobility nearly 100-fold as compared with standard film preparation by spin-coating, and nearly 10-fold increase over the benefits of pre-aggregation alone. In situ quartz crystal microbalance with dissipation (QCM-D) experiments reveal enhanced deposition of pre-aggregates on surfaces modified with an alkyl-terminated self-assembled monolayer (SAM) in comparison to un-aggregated polymer chains. Additional investigations reveal the combined pre-aggregation and surface functionalization significantly enhances local order of the conjugated polymer through planarization and extension of the conjugated backbone of the polymer which clearly translate to significant improvements of carrier transport at the semiconductor-dielectric interface in organic thin film transistors. This study points to opportunities in combining complementary routes, such as well-known pre-aggregation with substrate chemical functionalization, to enhance the polymer self-assembly and improve its interfacial order with benefits for transport properties.
Quantum transport in graphene in presence of strain-induced pseudo-Landau levels
DEFF Research Database (Denmark)
Settnes, Mikkel; Leconte, Nicolas; Barrios-Vargas, Jose E.
2016-01-01
up to several hundreds of Tesla, values inaccessible by real magnetic fields. Strain-induced pLLs yield enhanced scattering effects across the energy spectrum resulting in lower mean free path and enhanced localization effects. In the vicinity of the zeroth order pLL, we demonstrate an anomalous...
Chirped InAs/InP quantum-dash laser with enhanced broad spectrum of stimulated emission
Khan, Mohammed Zahed Mustafa
2013-03-01
We report on the demonstration of 50 nm (full-width at half-maximum) broadband stimulated emission from a chirped AlGaInAs barrier thickness multi-stack InAs/InP quantum dash (Qdash) laser. The 2 ?m wide uncoated Fabry-Perot (FP) ridge-waveguide laser exhibits a total power of 0.18 W, corresponding to an average spectral power density of 3.5 mW/nm, under pulsed current conditions. Intentional extended inhomogeneity across the Qdash stacks have been attributed to the enhancement of broadband emission. © 2013 American Institute of Physics.
Lu, Zhisong; Guo, Chun Xian; Yang, Hong Bin; Qiao, Yan; Guo, Jun; Li, Chang Ming
2011-01-15
Although CdTe nanocrystal has been applied in quantum dot (QD)-based solar cells, there is no report on a graphene-CdTe QD hybrid system and its photoresponses. In this work, graphene-CdTe QD composed nanosheets were one-step synthesized in aqueous solution using a hydrothermal method and demonstrated enhanced photoresponses, rendering potentials in optoelectronics applications. This work could provide an environmental-friendly and universal approach to fabricate graphene-based hybrid nanomaterials for various applications. Copyright © 2010 Elsevier Inc. All rights reserved.
DEFF Research Database (Denmark)
Chaban, Vitaly V.; Prezhdo, Victor; Prezhdo, Oleg
2013-01-01
Nonadiabatic molecular dynamics combined with time-domain density functional theory are used to study electron transfer (ET) from a CdSe quantum dot (QD) to the C-60 fullerene, occurring in several types of hybrid organic/inorganic nanocomposites. By unveiling the time dependence of the ET process......, it leads to a notably weaker QD-C-60 interaction than a lengthy molecular bridge. We show that the ET rate in a nonbonded mixture of QDs and C-60 can be enhanced by doping. The photoinduced ET is promoted primarily by mid- and low-frequency vibrations. The study establishes the basic design principles...
Spin Transport in a Rashba Ring-Quantum Dot System Pumped by Microwave Fields
International Nuclear Information System (INIS)
Zhang Lin; Wang Jun
2011-01-01
We report a theoretical study on producing electrically spin-polarized current in the Rashba ring with parallel double dots embedded, which are subject to two time-dependent microwave fields. By means of the Keldysh Green's function method, we present an analytic result of the pumped current at adiabatic limit and demonstrate that the interplay between the quantum pumping effect and spin-dependent quantum interference can lead to an arbitrarily controllable spin-polarized current in the device. The magnitude and direction of the charge and spin current can be effectively modulated by system parameters such as the pumping phase difference, Rashba precession phase, and the dynamic phase difference of electron traveling in two arms of ring; moreover, the spin-polarization degree of the charge current can also be tuned in the range [-∞, +∞]. Our findings may shed light on the all-electric way to produce the controllable spin-polarized charge current in the field of spintronics. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Chen, Yanli; Tao, Qiang; Fu, Wuyou; Yang, Haibin; Zhou, Xiaoming; Su, Shi; Ding, Dong; Mu, Yannan; Li, Xue; Li, Minghui
2014-08-28
The enhanced photoelectric performance of quantum dot sensitized solar cells via hydrogenated TiO2 is proposed. The best energy conversion efficiency is 1.5 times higher than cells without hydrogen treatment. We demonstrated that introducing oxygen vacancies by hydrogenation is an effective and feasible method for enhanced photoelectric performance.
Cluster-state quantum computing enhanced by high-fidelity generalized measurements.
Biggerstaff, D N; Kaltenbaek, R; Hamel, D R; Weihs, G; Rudolph, T; Resch, K J
2009-12-11
We introduce and implement a technique to extend the quantum computational power of cluster states by replacing some projective measurements with generalized quantum measurements (POVMs). As an experimental demonstration we fully realize an arbitrary three-qubit cluster computation by implementing a tunable linear-optical POVM, as well as fast active feedforward, on a two-qubit photonic cluster state. Over 206 different computations, the average output fidelity is 0.9832+/-0.0002; furthermore the error contribution from our POVM device and feedforward is only of O(10(-3)), less than some recent thresholds for fault-tolerant cluster computing.
DEFF Research Database (Denmark)
Chen, Yaohui; Mørk, Jesper
2011-01-01
In this paper we review our theoretical work on slow and fast light effects in quantum dot semiconductor optical amplifiers (QD SOAs), in particular we investigate the carrier dynamical contributions to the dynamic gain grating and cross gain modulation induced by unique ultrafast inter-subband c......In this paper we review our theoretical work on slow and fast light effects in quantum dot semiconductor optical amplifiers (QD SOAs), in particular we investigate the carrier dynamical contributions to the dynamic gain grating and cross gain modulation induced by unique ultrafast inter...
Heat transport in the XXZ spin chain: from ballistic to diffusive regimes and dephasing enhancement
International Nuclear Information System (INIS)
Mendoza-Arenas, J J; Al-Assam, S; Clark, S R; Jaksch, D
2013-01-01
In this work we study the heat transport in an XXZ spin-1/2 Heisenberg chain with homogeneous magnetic field, incoherently driven out of equilibrium by reservoirs at the boundaries. We focus on the effect of bulk dephasing (energy-dissipative) processes in different parameter regimes of the system. The non-equilibrium steady state of the chain is obtained by simulating its evolution under the corresponding Lindblad master equation, using the time evolving block decimation method. In the absence of dephasing, the heat transport is ballistic for weak interactions, while being diffusive in the strongly interacting regime, as evidenced by the heat current scaling with the system size. When bulk dephasing takes place in the system, diffusive transport is induced in the weakly interacting regime, with the heat current monotonically decreasing with the dephasing rate. In contrast, in the strongly interacting regime, the heat current can be significantly enhanced by dephasing for systems of small size. (paper)
DEFF Research Database (Denmark)
Larsen, Brian Roland; Holm, Rikke; Vilsen, Bente
2016-01-01
, in addition, Na+/K+-ATPase-mediated K+ clearance could be governed by astrocytic [Na+]i. During most neuronal activity, glutamate is released in the synaptic cleft and is re-absorbed by astrocytic Na+-coupled glutamate transporters, thereby elevating [Na+]i. It thus remains unresolved whether the different Na......+/K+-ATPase isoforms are controlled by [K+]o or [Na+]i during neuronal activity. Hippocampal slice recordings of stimulus-induced [K+]o transients with ion-sensitive microelectrodes revealed reduced Na+/K+-ATPase-mediated K+ management upon parallel inhibition of the glutamate transporter. The apparent intracellular...... isoforms than the β2 isoform. In summary, enhanced astrocytic Na+/K+-ATPase-dependent K+ clearance was obtained with parallel glutamate transport activity. The astrocytic Na+/K+-ATPase isoform constellation α2β1 appeared to be specifically geared to respond to the [Na+]i transients associated with activity...
Azagury, Aharon; Amar-Lewis, Eliz; Appel, Reut; Hallak, Mordechai; Kost, Joseph
2017-08-01
Chemical penetration enhancers (CPEs) have long been used for mass transport enhancement across membranes. Many CPEs are used in a solution or gel and could be a solvent. The use of CPEs is mainly limited due to their toxicity/irritation levels. This study presents the evaluation of encapsulated CPEs in nano-sized polymeric particles on the chorioamnion (CA) membrane mass transport. CPEs' mass encapsulated in nanoparticles was decreased by 10,000-fold. Interestingly, this approach resulted in a 6-fold increase in mass transport across the CA. This approach may also be used with other CPEs' base applications necessitating lower CPE concentration. Applying Ultrasound (US) has shown to increase the release rate of and also the mass transport across the CA membrane. It is proposed that encapsulated CPEs penetrate into the CA membrane thus prolonging their exposure, possibly extending their penetration into the CA membrane, while insonation also deepens their penetration into the CA membrane. Copyright © 2017 Elsevier B.V. All rights reserved.
Reactive Transport Modeling of Microbe-mediated Fe (II) Oxidation for Enhanced Oil Recovery
Surasani, V.; Li, L.
2011-12-01
Microbially Enhanced Oil Recovery (MEOR) aims to improve the recovery of entrapped heavy oil in depleted reservoirs using microbe-based technology. Reservoir ecosystems often contain diverse microbial communities those can interact with subsurface fluids and minerals through a network of nutrients and energy fluxes. Microbe-mediated reactions products include gases, biosurfactants, biopolymers those can alter the properties of oil and interfacial interactions between oil, brine, and rocks. In addition, the produced biomass and mineral precipitates can change the reservoir permeability profile and increase sweeping efficiency. Under subsurface conditions, the injection of nitrate and Fe (II) as the electron acceptor and donor allows bacteria to grow. The reaction products include minerals such as Fe(OH)3 and nitrogen containing gases. These reaction products can have large impact on oil and reservoir properties and can enhance the recovery of trapped oil. This work aims to understand the Fe(II) oxidation by nitrate under conditions relevant to MEOR. Reactive transport modeling is used to simulate the fluid flow, transport, and reactions involved in this process. Here we developed a complex reactive network for microbial mediated nitrate-dependent Fe (II) oxidation that involves both thermodynamic controlled aqueous reactions and kinetic controlled Fe (II) mineral reaction. Reactive transport modeling is used to understand and quantify the coupling between flow, transport, and reaction processes. Our results identify key parameter controls those are important for the alteration of permeability profile under field conditions.
International Nuclear Information System (INIS)
Biwer, B.M.; LePoire, D.J.; Chen, S.Y.
1996-01-01
The RISKIND computer program was developed for the analysis of radiological consequences and health risks to individuals and the collective population from exposures associated with the transportation of spent nuclear fuel (SNF) or other radioactive materials. The code is intended to provide scenario-specific analyses when evaluating alternatives for environmental assessment activities, including those for major federal actions involving radioactive material transport as required by the National Environmental Policy Act (NEPA). As such, rigorous procedures have been implemented to enhance the code's credibility and strenuous efforts have been made to enhance ease of use of the code. To increase the code's reliability and credibility, a new version of RISKIND was produced under a quality assurance plan that covered code development and testing, and a peer review process was conducted. During development of the new version, the flexibility and ease of use of RISKIND were enhanced through several major changes: (1) a Windows trademark point-and-click interface replaced the old DOS menu system, (2) the remaining model input parameters were added to the interface, (3) databases were updated, (4) the program output was revised, and (5) on-line help has been added. RISKIND has been well received by users and has been established as a key component in radiological transportation risk assessments through its acceptance by the U.S. Department of Energy community in recent environmental impact statements (EISs) and its continued use in the current preparation of several EISs
Arango, Yulieth C.; Huang, Liubing; Chen, Chaoyu; Avila, Jose; Asensio, Maria C.; Grützmacher, Detlev; Lüth, Hans; Lu, Jia Grace; Schäpers, Thomas
2016-01-01
We report on low-temperature transport and electronic band structure of p-type Sb2Te3 nanowires, grown by chemical vapor deposition. Magnetoresistance measurements unravel quantum interference phenomena, which depend on the cross-sectional dimensions of the nanowires. The observation of periodic Aharonov-Bohm-type oscillations is attributed to transport in topologically protected surface states in the Sb2Te3 nanowires. The study of universal conductance fluctuations demonstrates coherent transport along the Aharonov-Bohm paths encircling the rectangular cross-section of the nanowires. We use nanoscale angle-resolved photoemission spectroscopy on single nanowires (nano-ARPES) to provide direct experimental evidence on the nontrivial topological character of those surface states. The compiled study of the bandstructure and the magnetotransport response unambiguosly points out the presence of topologically protected surface states in the nanowires and their substantial contribution to the quantum transport effects, as well as the hole doping and Fermi velocity among other key issues. The results are consistent with the theoretical description of quantum transport in intrinsically doped quasi-one-dimensional topological insulator nanowires. PMID:27581169
Mullin, Jonathan; Valley, Nicholas; Blaber, Martin G; Schatz, George C
2012-09-27
Multiscale models that combine quantum mechanics and classical electrodynamics are presented, which allow for the evaluation of surface-enhanced Raman (SERS) and hyper-Raman scattering spectra (SEHRS) for both chemical (CHEM) and electrodynamic (EM) enhancement mechanisms. In these models, time-dependent density functional theory (TDDFT) for a system consisting of the adsorbed molecule and a metal cluster fragment of the metal particle is coupled to Mie theory for the metal particle, with the surface of the cluster being overlaid with the surface of the metal particle. In model A, the electromagnetic enhancement from plasmon-excitation of the metal particle is combined with the chemical enhancement associated with a static treatment of the molecule-metal structure to determine overall spectra. In model B, the frequency dependence of the Raman spectrum of the isolated molecule is combined with the enhancements determined in model A to refine the enhancement estimate. An equivalent theory at the level of model A is developed for hyper-Raman spectra calculations. Application to pyridine interacting with a 20 nm diameter silver sphere is presented, including comparisons with an earlier model (denoted G), which combines plasmon enhanced fields with gas-phase Raman (or hyper-Raman) spectra. The EM enhancement factor for spherical particles at 357 nm is found to be 10(4) and 10(6) for SERS and SEHRS, respectively. Including both chemical and electromagnetic mechanisms at the level of model A leads to enhancements on the order of 10(4) and 10(9) for SERS and SEHRS.
Akhavan, Nima Dehdashti; Afzalian, Aryan; Lee, Chi-Woo; Yan, Ran; Ferain, Isabelle; Razavi, Pedram; Yu, Ran; Fagas, Giorgos; Colinge, Jean-Pierre
2010-08-01
In this paper we investigate the effects of intravalley acoustic phonon scattering on the quantum transport and on the electrical characteristics of multigate silicon nanowire metal-oxide-semiconductor field-effect transistors. We show that acoustic phonons cause a shift and broadening of the local DOS in the nanowire, which modifies the electrical characteristics of the device. The influence of scattering on off-state and on-state currents is investigated for different values of channel length. In the ballistic transport regime, source-to-drain tunneling current is predominant, whereas in the presence of acoustic phonons, diffusion becomes the dominant current transport mechanism. A three-dimensional quantum mechanical device simulator based on the nonequilibrium Green's function formalism in uncoupled-mode space has been developed to extract device parameters in the presence of electron-phonon interactions. Electron-phonon scattering is accounted for by adopting the self-consistent Born approximation and using the deformation potential theory.
International Nuclear Information System (INIS)
Bauer, Thilo; Jäger, Christof M.; Jordan, Meredith J. T.; Clark, Timothy
2015-01-01
We have developed a multi-agent quantum Monte Carlo model to describe the spatial dynamics of multiple majority charge carriers during conduction of electric current in the channel of organic field-effect transistors. The charge carriers are treated by a neglect of diatomic differential overlap Hamiltonian using a lattice of hydrogen-like basis functions. The local ionization energy and local electron affinity defined previously map the bulk structure of the transistor channel to external potentials for the simulations of electron- and hole-conduction, respectively. The model is designed without a specific charge-transport mechanism like hopping- or band-transport in mind and does not arbitrarily localize charge. An electrode model allows dynamic injection and depletion of charge carriers according to source-drain voltage. The field-effect is modeled by using the source-gate voltage in a Metropolis-like acceptance criterion. Although the current cannot be calculated because the simulations have no time axis, using the number of Monte Carlo moves as pseudo-time gives results that resemble experimental I/V curves
In Vivo EPR Resolution Enhancement Using Techniques Known from Quantum Computing Spin Technology.
Rahimi, Robabeh; Halpern, Howard J; Takui, Takeji
2017-01-01
A crucial issue with in vivo biological/medical EPR is its low signal-to-noise ratio, giving rise to the low spectroscopic resolution. We propose quantum hyperpolarization techniques based on 'Heat Bath Algorithmic Cooling', allowing possible approaches for improving the resolution in magnetic resonance spectroscopy and imaging.
Quantum nondemolition measurement with a nonclassical meter input and an electro-optic enhancement
DEFF Research Database (Denmark)
Andersen, Ulrik Lund; Buchler, B.C.; Bachor, H.A.
2002-01-01
Optical quantum nondemolition measurements are performed using a beamsplitter with a nonclassical meter input and a electro-optic feedforward loop. The nonclassical meter input is provided by a stable 4.5 dB amplitude squeezed source generated by an optical parametric amplifier. We show...
DEFF Research Database (Denmark)
Utko, Pawel; Hansen, Jørn Bindslev; Lindelof, Poul Erik
2007-01-01
We have investigated the response of the acoustoelectric-current driven by a surface-acoustic wave through a quantum point contact in the closed-channel regime. Under proper conditions, the current develops plateaus at integer multiples of ef when the frequency f of the surface-acoustic wave...... or the gate voltage V-g of the point contact is varied. A pronounced 1.1 MHz beat period of the current indicates that the interference of the surface-acoustic wave with reflected waves matters. This is supported by the results obtained after a second independent beam of surface-acoustic wave was added......, though at different current values, as if they were superposed on each other. Their presence could result from two independent quantization mechanisms for the acoustoelectric-current. We point out that short potential barriers determining the properties of our nominally long constrictions could lead...