Two-Channel Kondo Effect in a Modified Single Electron Transistor
Oreg, Yuval; Goldhaber-Gordon, David
2003-04-01
We suggest a simple system of two electron droplets which should display two-channel Kondo behavior at experimentally accessible temperatures. Stabilization of the two-channel Kondo fixed point requires fine control of the electrochemical potential in each droplet, which can be achieved by adjusting voltages on nearby gate electrodes. We study the conditions for obtaining this type of two-channel Kondo behavior, discuss the experimentally observable consequences, and explore the generalization to the multichannel Kondo case.
Charge Fractionalization in the Two-Channel Kondo Effect
Landau, L. Aviad; Cornfeld, Eyal; Sela, Eran
2018-05-01
The phenomenon of charge fractionalization describes the emergence of novel excitations with fractional quantum numbers, as predicted in strongly correlated systems such as spin liquids. We elucidate that precisely such an unusual effect may occur in the simplest possible non-Fermi liquid, the two-channel Kondo effect. To bring this concept down to experimental test, we study nonequilibrium transport through a device realizing the charge two-channel Kondo critical point in a recent experiment by Iftikhar et al. [Nature (London) 526, 233 (2015), 10.1038/nature15384]. The shot noise at low voltages is predicted to result in a universal Fano factor e*/e =1 /2 . This allows us to experimentally identify elementary transport processes of emergent fermions carrying half-integer charge.
From four- to two-channel Kondo effect in junctions of XY spin chains
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Domenico Giuliano
2016-08-01
Full Text Available We consider the Kondo effect in Y-junctions of anisotropic XY models in an applied magnetic field along the critical lines characterized by a gapless excitation spectrum. We find that, while the boundary interaction Hamiltonian describing the junction can be recasted in the form of a four-channel, spin-1/2 antiferromagnetic Kondo Hamiltonian, the number of channels effectively participating in the Kondo effect depends on the chain parameters, as well as on the boundary couplings at the junction. The system evolves from an effective four-channel topological Kondo effect for a junction of XX-chains with symmetric boundary couplings into a two-channel one at a junction of three quantum critical Ising chains. The effective number of Kondo channels depends on the properties of the boundary and of the bulk. The XX-line is a “critical” line, where a four-channel topological Kondo effect can be recovered by fine-tuning the boundary parameter, while along the line in parameter space connecting the XX-line and the critical Ising point the junction is effectively equivalent to a two-channel topological Kondo Hamiltonian. Using a renormalization group approach, we determine the flow of the boundary couplings, which allows us to define and estimate the critical couplings and Kondo temperatures of the different Kondo (pair channels. Finally, we study the local transverse magnetization in the center of the Y-junction, eventually arguing that it provides an effective tool to monitor the onset of the two-channel Kondo effect.
From four- to two-channel Kondo effect in junctions of XY spin chains
International Nuclear Information System (INIS)
Giuliano, Domenico; Sodano, Pasquale; Tagliacozzo, Arturo; Trombettoni, Andrea
2016-01-01
We consider the Kondo effect in Y-junctions of anisotropic XY models in an applied magnetic field along the critical lines characterized by a gapless excitation spectrum. We find that, while the boundary interaction Hamiltonian describing the junction can be recasted in the form of a four-channel, spin-1/2 antiferromagnetic Kondo Hamiltonian, the number of channels effectively participating in the Kondo effect depends on the chain parameters, as well as on the boundary couplings at the junction. The system evolves from an effective four-channel topological Kondo effect for a junction of XX-chains with symmetric boundary couplings into a two-channel one at a junction of three quantum critical Ising chains. The effective number of Kondo channels depends on the properties of the boundary and of the bulk. The XX-line is a “critical” line, where a four-channel topological Kondo effect can be recovered by fine-tuning the boundary parameter, while along the line in parameter space connecting the XX-line and the critical Ising point the junction is effectively equivalent to a two-channel topological Kondo Hamiltonian. Using a renormalization group approach, we determine the flow of the boundary couplings, which allows us to define and estimate the critical couplings and Kondo temperatures of the different Kondo (pair) channels. Finally, we study the local transverse magnetization in the center of the Y-junction, eventually arguing that it provides an effective tool to monitor the onset of the two-channel Kondo effect.
From four- to two-channel Kondo effect in junctions of XY spin chains
Energy Technology Data Exchange (ETDEWEB)
Giuliano, Domenico, E-mail: domenico.giuliano@fis.unical.it [Dipartimento di Fisica, Università della Calabria, Arcavacata di Rende I-87036, Cosenza (Italy); INFN, Gruppo collegato di Cosenza, Arcavacata di Rende I-87036, Cosenza (Italy); Sodano, Pasquale, E-mail: pasquale.sodano02@gmail.com [International Institute of Physics, Universidade Federal do Rio Grande do Norte, 59078-400 Natal, RN (Brazil); Departemento de Física Teorica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, RN (Brazil); Tagliacozzo, Arturo, E-mail: arturo.tagliacozzo@na.infn.it [INFN, Gruppo collegato di Cosenza, Arcavacata di Rende I-87036, Cosenza (Italy); Dipartimento di Fisica, Università di Napoli “Federico II”, Monte S. Angelo-Via Cintia, I-80126 Napoli (Italy); CNR-SPIN, Monte S. Angelo-Via Cintia, I-80126 Napoli (Italy); Trombettoni, Andrea, E-mail: andreatr@sissa.it [CNR-IOM DEMOCRITOS Simulation Center, Via Bonomea 265, I-34136 Trieste (Italy); SISSA and INFN, Sezione di Trieste, Via Bonomea 265, I-34136 Trieste (Italy)
2016-08-15
We consider the Kondo effect in Y-junctions of anisotropic XY models in an applied magnetic field along the critical lines characterized by a gapless excitation spectrum. We find that, while the boundary interaction Hamiltonian describing the junction can be recasted in the form of a four-channel, spin-1/2 antiferromagnetic Kondo Hamiltonian, the number of channels effectively participating in the Kondo effect depends on the chain parameters, as well as on the boundary couplings at the junction. The system evolves from an effective four-channel topological Kondo effect for a junction of XX-chains with symmetric boundary couplings into a two-channel one at a junction of three quantum critical Ising chains. The effective number of Kondo channels depends on the properties of the boundary and of the bulk. The XX-line is a “critical” line, where a four-channel topological Kondo effect can be recovered by fine-tuning the boundary parameter, while along the line in parameter space connecting the XX-line and the critical Ising point the junction is effectively equivalent to a two-channel topological Kondo Hamiltonian. Using a renormalization group approach, we determine the flow of the boundary couplings, which allows us to define and estimate the critical couplings and Kondo temperatures of the different Kondo (pair) channels. Finally, we study the local transverse magnetization in the center of the Y-junction, eventually arguing that it provides an effective tool to monitor the onset of the two-channel Kondo effect.
Emery-Kivelson solution of the two-channel Kondo problem
Sengupta, Anirvan M.; Georges, Antoine
1994-04-01
We consider the two-channel Kondo model in the Emery-Kivelson approach, and calculate the total susceptibility enhancement due to the impurity χimp=χ-χbulk. We find that χimp exactly vanishes at the solvable point, in a completely analogous way to the singular part of the specific heat Cimp. A perturbative calculation around the solvable point yields the generic behavior χimp~log(1/T), Cimp~T logT and the known universal value of the Wilson ratio RW=8/3. From this calculation, the Kondo temperature can be identified and is found to behave as the inverse square of the perturbation parameter. The small-field, zero-temperature behavior χimp~log(1/h) is also recovered.
International Nuclear Information System (INIS)
Zhang Yumei; Chen Hong.
1995-09-01
The effects of the repulsion between the electrons on the two-channel Kondo problem are studied by use of the bosonization technique. Following Emery and Kivelson, we define a special case in the spin density wave sector, in which the impurity spin is actually detached from the dynamics of the electrons. The model is thus mapped to a local Sine-Gordon system. For weak repulsion, the basic features of the overscreening picture are maintained. However, at sufficient strong repulsion the system is driven into the weak coupling regime, hence an overscreening-underscreening transition emerges. (author). 22 refs
Zhuravlev, A. K.; Anokhin, A. O.; Irkhin, V. Yu.
2018-02-01
Simple scaling consideration and NRG solution of the one- and two-channel Kondo model in the presence of a logarithmic Van Hove singularity at the Fermi level is given. The temperature dependences of local and impurity magnetic susceptibility and impurity entropy are calculated. The low-temperature behavior of the impurity susceptibility and impurity entropy turns out to be non-universal in the Kondo sense and independent of the s-d coupling J. The resonant level model solution in the strong coupling regime confirms the NRG results. In the two-channel case the local susceptibility demonstrates a non-Fermi-liquid power-law behavior.
Two-Channel Kondo Physics due to As Vacancies in the Layered Compound ZrAs1.58Se0.39
Kirchner, Stefan; Cichorek, T.; Bochenek, L.; Schmidt, M.; Niewa, R.; Czuluccki, A.; Auffermann, G.; Steglich, F.; Kniep, R.
We address the origin of the magnetic-field independent - | A | T 1 / 2 term observed in the low-temperature resistivity of several As-based metallic systems of the PbFCl structure type. For the layered compound ZrAs1.58Se0.39, we show that vacancies in the square nets of As give rise to the low-temperature transport anomaly over a wide temperature regime of almost two decades in temperature. This low-temperature behavior is in line with the non-magnetic version of the two-channel Kondo effect, whose origin we ascribe to a dynamic Jahn-Teller effect operating at the vacancy-carrying As layer with a C4 symmetry. The pair-breaking nature of the dynamical defects in the square nets of As explains the low superconducting transition temperature Tc 0 . 14 K of ZrAs1.58Se0.39, as compared to the free-of-vacancies homologue ZrP1.54S0.46 (Tc 3 . 7 K). Our findings should be relevant to a wide class of metals with disordered pnictogen layers.
Self-sustained oscillations in nanoelectromechanical systems induced by Kondo resonance
International Nuclear Information System (INIS)
Song, Taegeun; Kiselev, Mikhail N; Kikoin, Konstantin; Shekhter, Robert I; Gorelik, Leonid Y
2014-01-01
We investigate the instability and dynamical properties of nanoelectromechanical systems represented by a single-electron device containing movable quantum dots attached to a vibrating cantilever via asymmetric tunnel contacts. The Kondo resonance in electron tunneling between the source and shuttle facilitates self-sustained oscillations originating from the strong coupling of mechanical and electronic/spin degrees of freedom. We analyze a stability diagram for the two-channel Kondo shuttling regime due to limitations given by the electromotive force acting on a moving shuttle, and find that the saturation oscillation amplitude is associated with the retardation effect of the Kondo cloud. The results shed light on possible ways to experimentally realize the Kondo-cloud dynamical probe by using high mechanical dissipation tunability as well as supersensitive detection of mechanical displacement
Self-sustained oscillations in nanoelectromechanical systems induced by Kondo resonance
Song, Taegeun; Kiselev, Mikhail N.; Kikoin, Konstantin; Shekhter, Robert I.; Gorelik, Leonid Y.
2014-03-01
We investigate the instability and dynamical properties of nanoelectromechanical systems represented by a single-electron device containing movable quantum dots attached to a vibrating cantilever via asymmetric tunnel contacts. The Kondo resonance in electron tunneling between the source and shuttle facilitates self-sustained oscillations originating from the strong coupling of mechanical and electronic/spin degrees of freedom. We analyze a stability diagram for the two-channel Kondo shuttling regime due to limitations given by the electromotive force acting on a moving shuttle, and find that the saturation oscillation amplitude is associated with the retardation effect of the Kondo cloud. The results shed light on possible ways to experimentally realize the Kondo-cloud dynamical probe by using high mechanical dissipation tunability as well as supersensitive detection of mechanical displacement.
Response of Kondo lattice systems to pressure
International Nuclear Information System (INIS)
Thompson, J.D.; Borges, H.A.; Fisk, Z.; Horn, S.; Parks, R.D.; Wells, G.L.
1987-01-01
Yb-based Kondo lattice systems (YbAgCu 4 , YbCu 2 Si 2 , YbRh 2 Si 2 ) represent an interesting class of materials in which it is possible to study systematically the development of heavy electron behavior through the application of pressure. Certainly, additional experiments are required to determine to what extent Yb compounds are mirror images of their Ce counterparts. Finally, pressure reveals the presence of competing interactions for which a simple model exists that qualitatively accounts for the pressure response observed in a large number of Ce, U and Yb-based Kondo lattice systems
Polarized object detection in crabs: a two-channel system.
Basnak, Melanie Ailín; Pérez-Schuster, Verónica; Hermitte, Gabriela; Berón de Astrada, Martín
2018-05-25
Many animal species take advantage of polarization vision for vital tasks such as orientation, communication and contrast enhancement. Previous studies have suggested that decapod crustaceans use a two-channel polarization system for contrast enhancement. Here, we characterize the polarization contrast sensitivity in a grapsid crab . We estimated the polarization contrast sensitivity of the animals by quantifying both their escape response and changes in heart rate when presented with polarized motion stimuli. The motion stimulus consisted of an expanding disk with an 82 deg polarization difference between the object and the background. More than 90% of animals responded by freezing or trying to avoid the polarized stimulus. In addition, we co-rotated the electric vector (e-vector) orientation of the light from the object and background by increments of 30 deg and found that the animals' escape response varied periodically with a 90 deg period. Maximum escape responses were obtained for object and background e-vectors near the vertical and horizontal orientations. Changes in cardiac response showed parallel results but also a minimum response when e-vectors of object and background were shifted by 45 deg with respect to the maxima. These results are consistent with an orthogonal receptor arrangement for the detection of polarized light, in which two channels are aligned with the vertical and horizontal orientations. It has been hypothesized that animals with object-based polarization vision rely on a two-channel detection system analogous to that of color processing in dichromats. Our results, obtained by systematically varying the e-vectors of object and background, provide strong empirical support for this theoretical model of polarized object detection. © 2018. Published by The Company of Biologists Ltd.
Development of a Two-Channel Simultaneous Photoplethysmography Recording System
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Kim Soon Chong
2013-09-01
Full Text Available Multi-site photoplethysmograph (PPG recording enables researchers to study the vascular and hemodynamic properties of human subjects. Currently, there is no commercial system available in the market to perform either one channel or multi-channel PPG recording. PPG is an optoelectronic technique that measures changes in blood volume associated with cardiac contraction. The measurements can be obtained from fingertips, ear lobes and toes due to their low absorption and high degree of vasculature. The main objective of this project is to develop a two-channel simultaneous PPG recording system to acquire PPG signals from two different physiological sites using a Nellcor equivalent PPG probe. MATLAB software was used during the development phase to ensure rapid prototyping. The experiment results show that there was no inter -channel delay in the developed two-channel PPG system. Our preliminary results show that the delays between the left and the right arm were from 4 to 12 ms in three healthy random subjects. The system is portable, powered by universal serial bus (USB and allows the user to do the PPG data acquisition in a clinical setting.
Voltage Quench Dynamics of a Kondo System.
Antipov, Andrey E; Dong, Qiaoyuan; Gull, Emanuel
2016-01-22
We examine the dynamics of a correlated quantum dot in the mixed valence regime. We perform numerically exact calculations of the current after a quantum quench from equilibrium by rapidly applying a bias voltage in a wide range of initial temperatures. The current exhibits short equilibration times and saturates upon the decrease of temperature at all times, indicating Kondo behavior both in the transient regime and in the steady state. The time-dependent current saturation temperature connects the equilibrium Kondo temperature to a substantially increased value at voltages outside of the linear response. These signatures are directly observable by experiments in the time domain.
International Nuclear Information System (INIS)
Posske, Thore Hagen
2016-01-01
Topological insulators are electronic phases that insulate in the bulk and accommodate a peculiar, metallic edge liquid with a spin-dependent dispersion. They are regarded to be of considerable future use in spintronics and for quantum computation. Besides determining the intrinsic properties of this rather novel electronic phase, considering its combination with well-known physical systems can generate genuinely new physics. In this thesis, we report on such combinations including topological insulators. Specifically, we analyze an attached Rashba impurity, a Kondo dot in the two channel setup, magnetic impurities on the surface of a strong three-dimensional topological insulator, the proximity coupling of the latter system to a superconductor, and hybrid systems consisting of a topological insulator and a semimetal. Let us summarize our primary results. Firstly, we determine an analytical formula for the Kondo cloud and describe its possible detection in current correlations far away from the Kondo region. We thereby rely on and extend the method of refermionizable points. Furthermore, we find a class of gapless topological superconductors and semimetals, which accommodate edge states that behave similarly to the ones of globally gapped topological phases. Unexpectedly, we also find edge states that change their chirality when affected by sufficiently strong disorder. We regard the presented research helpful in future classifications and applications of systems containing topological insulators, of which we propose some examples.
Energy Technology Data Exchange (ETDEWEB)
Posske, Thore Hagen
2016-02-26
Topological insulators are electronic phases that insulate in the bulk and accommodate a peculiar, metallic edge liquid with a spin-dependent dispersion. They are regarded to be of considerable future use in spintronics and for quantum computation. Besides determining the intrinsic properties of this rather novel electronic phase, considering its combination with well-known physical systems can generate genuinely new physics. In this thesis, we report on such combinations including topological insulators. Specifically, we analyze an attached Rashba impurity, a Kondo dot in the two channel setup, magnetic impurities on the surface of a strong three-dimensional topological insulator, the proximity coupling of the latter system to a superconductor, and hybrid systems consisting of a topological insulator and a semimetal. Let us summarize our primary results. Firstly, we determine an analytical formula for the Kondo cloud and describe its possible detection in current correlations far away from the Kondo region. We thereby rely on and extend the method of refermionizable points. Furthermore, we find a class of gapless topological superconductors and semimetals, which accommodate edge states that behave similarly to the ones of globally gapped topological phases. Unexpectedly, we also find edge states that change their chirality when affected by sufficiently strong disorder. We regard the presented research helpful in future classifications and applications of systems containing topological insulators, of which we propose some examples.
Kondo effect in three-dimensional Dirac and Weyl systems
Mitchell, Andrew K.; Fritz, Lars
2015-01-01
Magnetic impurities in three-dimensional Dirac and Weyl systems are shown to exhibit a fascinatingly diverse range of Kondo physics, with distinctive experimental spectroscopic signatures. When the Fermi level is precisely at the Dirac point, Dirac semimetals are in fact unlikely candidates for a
Three stage Kondo effect in a three quantum dot system
Chiappe, Guillermo; Costa Ribeiro, Laercio; Hamad, Ignacio; Victoriano Anda, Enrique
2014-03-01
In this work we study the transport properties of a series connected three quantum dot (QD) system with local strong Coulomb interaction and with one of the extremity QD connected to two metallic leads. We evaluate the local density of states (LDOS) in the QDs and the conductance between the metallic leads considering different magnitudes for the coupling between the central and the extremity QD which is not connected to the leads (side QDs). For small magnitudes of this coupling the LDOS of the QD coupled to the leads present a Kondo resonance with a dip and a very tiny peak at the Fermi level. The widths of these structures are associated to three energy scales, or three Kondo temperatures, which characterizes the three stage Kondo regime. Increasing the coupling between the side QDs we observe a transition to the conventional Kondo regime. We use the multi-configuration Lanczos calculations and the finite U slave-boson mean-field theory. The results present qualitative and quantitative agreement.
Nonequilibrium Quasiparticle Distribution Induced by Kondo Defects
Kroha, J.; Zawadowski, A.
2002-04-01
It is shown that in resistive nanowires out of equilibrium containing either single- or two-channel Kondo impurities the distribution function f(E,U) obeys scaling behavior in terms of the quasiparticle energy E and the bias voltage U. The numerically calculated f(E,U) curves explain quantitatively recent experiments on Cu and Au nanowires. The systematics of the impurity concentration cimp extracted from the comparison between theory and results on various Cu and Au samples strongly suggests that in these systems the scaling arises from magnetic Kondo impurities.
Nuclear orientation studies of manganese in copper Kondo system
International Nuclear Information System (INIS)
Bakalyar, D.
1977-08-01
The internal field seen by the 54 Mn nuclei in a dilute (about 1 part per billion) manganese in copper Kondo system was measured using nuclear orientation. The measurements were made at temperatures on the order of 4 mK in applied fields of 5 kG to 40 kG. Temperatures were measured using a 60 Co in nickel nuclear orientation thermometer and were achieved by adiabatically demagnetizing an ingot of the hyperfine enhanced nuclear coolant PrCu 6 from temperatures of about 30 mK (the mixing chamber temperature of a dilution refrigerator). The data was temperature independent but there was evidence of iteractions between the manganese atoms at manganese concentrations of 1 / 2 part per million. The data was interpreted by assuming that the internal field consisted of the hyperfine field minus the applied field (i.e. the hyperfine field and applied field were aligned in opposite directions). The hyperfine field versus applied field data was compared to three approximate solutions to the Kondo Hamiltonian. Two of the solutions, one by Luther and Emery and the other by Goetze and Schlottmann, fit the data very well. The third solution, that proposed by Ishii, does not fit the data. Fitted to the data, the Luther-Emery solution predicts a saturation value of the hyperfine field of 303 kG whereas the Goetze-Schlottmann solution predicts a saturation value of 297 kG. The hyperfine field is only beginning to reach its saturation value with applied fields of 40 kG
Quantum phase transitions in multi-impurity and lattice Kondo systems
International Nuclear Information System (INIS)
Nejati, Ammar
2017-01-01
The main purpose of this dissertation is to provide a detailed development of a self-consistent perturbative renormalization group (RG) method to investigate the quantum phases and quantum phase transitions of multi-impurity Kondo systems (e.g., two impurities or a lattice of impurities). The essence of the RG method is an extension of the standard ''poor man's scaling'' by including the dynamical effects of the magnetic fluctuations in the Kondo vertex. Such magnetic fluctuations arise due to the indirect carrier-mediated exchange interaction (RKKY interaction) between the impurities and compete with the Kondo effect to determine the ground-state. The aim is to take the most 'economic' route and avoid intensive numerical computations as far as possible. In general, it is shown in detail how a relatively small amount of such magnetic fluctuations can suppress and ultimately, destroy the Kondo-screened phase in a universal manner, and without incurring a magnetic instability in the system. The renormalization group method and its extensions are further applied to several distinct experimental realization of the multi-impurity Kondo effect; namely, Kondo adatoms studied via scanning tunneling spectroscopy, a highly-tunable double-quantum-dot system based on semiconducting heterostructures, and finally, the heavy fermionic compounds as Kondo lattices. We demonstrate the qualitative and quantitative agreement of the RG theory with the experimental findings, which supports the validity of the method. In the case of Kondo lattices, we further include the possibility of a magnetic ordering in the lattice to see whether a magnetic ordering can happen simultaneously with or before the Kondo breakdown (or even prevent it altogether). In the last chapter, we consider the fate of the local moments in the absence of full Kondo screening while Kondo fluctuations are still present. This partially-screened phase needs itself an extensive study
Quantum phase transitions in multi-impurity and lattice Kondo systems
Energy Technology Data Exchange (ETDEWEB)
Nejati, Ammar
2017-01-16
The main purpose of this dissertation is to provide a detailed development of a self-consistent perturbative renormalization group (RG) method to investigate the quantum phases and quantum phase transitions of multi-impurity Kondo systems (e.g., two impurities or a lattice of impurities). The essence of the RG method is an extension of the standard ''poor man's scaling'' by including the dynamical effects of the magnetic fluctuations in the Kondo vertex. Such magnetic fluctuations arise due to the indirect carrier-mediated exchange interaction (RKKY interaction) between the impurities and compete with the Kondo effect to determine the ground-state. The aim is to take the most 'economic' route and avoid intensive numerical computations as far as possible. In general, it is shown in detail how a relatively small amount of such magnetic fluctuations can suppress and ultimately, destroy the Kondo-screened phase in a universal manner, and without incurring a magnetic instability in the system. The renormalization group method and its extensions are further applied to several distinct experimental realization of the multi-impurity Kondo effect; namely, Kondo adatoms studied via scanning tunneling spectroscopy, a highly-tunable double-quantum-dot system based on semiconducting heterostructures, and finally, the heavy fermionic compounds as Kondo lattices. We demonstrate the qualitative and quantitative agreement of the RG theory with the experimental findings, which supports the validity of the method. In the case of Kondo lattices, we further include the possibility of a magnetic ordering in the lattice to see whether a magnetic ordering can happen simultaneously with or before the Kondo breakdown (or even prevent it altogether). In the last chapter, we consider the fate of the local moments in the absence of full Kondo screening while Kondo fluctuations are still present. This partially-screened phase needs itself an extensive study
Hazard rate for a two-channel protective system subject to a high demand rate
International Nuclear Information System (INIS)
Oliveira, L.F.; Youngblood, R.; Melo, P.F.F.
1989-01-01
A basic figure of merit associated with a protective system for an industrial plant is the number of accidents expected to occur in the plant within a given period of time, with the system installed. By definition, in a plant equipped with a protective system, an accident can only happen if an initiating event (a demand) occurs while the protective system is unavailable, that is, while it is in one of its possible failed states. This means that the hazard rate or accident frequency depends on the demand rate and on the unavailability of the protective systems. It has long been recognized that the demand rate influences the unavailability of the protective system, and practical expressions incorporating that effect have been developed for single-channel (Lees, 1982) and multi-channel (Kumamoto and Henley 1978) protective systems. The effect has also been incorporated into a Markovian treatment of a plant protection system (Papazoglou and Cho, 1985). In a previous paper (Oliveira and Netto, 1987) a Markovian approach was used to derive analytical expressions for the evaluation of the plant hazard rate for a single-channel protective system, properly accounting for the effects of the demand and the repair rates. In this paper the authors present an extension of that model to the case of a plant equipped with a two-channel protective system
Directory of Open Access Journals (Sweden)
Kihong Shin
2015-01-01
Full Text Available Most existing techniques for machinery health monitoring that utilize measured vibration signals usually require measurement points to be as close as possible to the expected fault components of interest. This is particularly important for implementing condition-based maintenance since the incipient fault signal power may be too small to be detected if a sensor is located further away from the fault source. However, a measurement sensor is often not attached to the ideal point due to geometric or environmental restrictions. In such a case, many of the conventional diagnostic techniques may not be successfully applicable. In this paper, a two-channel analysis method is proposed to overcome such difficulty. It uses two vibration signals simultaneously measured at arbitrary points in a machine. The proposed method is described theoretically by introducing a fictitious system frequency response function. It is then verified experimentally for bearing fault detection. The results show that the suggested method may be a good alternative when ideal points for measurement sensors are not readily available.
Majorana bound states in two-channel time-reversal-symmetric nanowire systems
DEFF Research Database (Denmark)
Gaidamauskas, Erikas; Paaske, Jens; Flensberg, Karsten
2014-01-01
We consider time-reversal-symmetric two-channel semiconducting quantum wires proximity coupled to a conventional s-wave superconductor. We analyze the requirements for a non-trivial topological phase, and find that necessary conditions are 1) the determinant of the pairing matrix in channel space...
Koga, M.; Matsumoto, M.; Kusunose, H.
2018-05-01
We study a local antisymmetric spin-orbit (ASO) coupling effect on a triangular-triple-quantum-dot (TTQD) system as a theoretical proposal for a new application of the Kondo physics to nanoscale devices. The electric polarization induced by the Kondo effect is strongly correlated with the spin configurations and molecular orbital degrees of freedom in the TTQD. In particular, an abrupt sign reversal of the emergent electric polarization is associated with a quantum critical point in a magnetic field, which can also be controlled by the ASO coupling that changes the mixing weight of different orbital components in the TTQD ground state.
Energy Technology Data Exchange (ETDEWEB)
Gnida, D., E-mail: d.gnida@int.pan.wroc.pl [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wrocław (Poland); Dominyuk, N.; Zaremba, V. [Inorganic Chemistry Department, Ivan Franko Lviv National University, Kyryla and Mephodiya Str. 6, 79005 Lviv (Ukraine); Kaczorowski, D. [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wrocław (Poland)
2015-02-15
Highlights: • Interplay of Kondo and RKKY interactions in the presence of nonmagnetic disorder. • Suppression of the coherent Kondo state by nonmagnetic impurities. • Observation of quantum interference phenomena in Ce-based Kondo system. • Coexistence of incoherent Kondo effect and Altshuler-Aronov quantum correction. - Abstract: The alloy system CePd{sub 1−x}Ge{sub x}In with 0.1⩽x⩽0.4 was investigated by means of heat capacity and electrical resistivity measurements. Its low-temperature behavior has been found to be governed by the interplay of Kondo effect and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions in the presence of atomic disorder in nonmagnetic atoms sublattice. The coherent Kondo state, observed for CePdIn, gradually vanishes with increasing the Ge-content. The incoherent Kondo state, which characterizes Ge-rich alloys, appears very sensitive to applied magnetic field. The observed systematic changes in the temperature- and field-dependent electrical transport in CePd{sub 1−x}Ge{sub x}In manifest the important role of quantum correction due to electron-electron interactions in weakly localized regime.
Lai, Hsin-Hua; Nica, Emilian; Si, Qimiao
Motivated by the properties of the heavy-fermion Ce3Pd20Si6 compound which exhibits both antiferro-magnetic (AFM) and antiferro-quadrupolar (AFQ) orders, we study a simplified quantum non-linear sigma model for spin-1 systems, with generalized multi-pole Kondo couplings to conduction electrons. We first consider the case when an SU(3) symmetry relates the spin and quadrupolar channels. We then analyze the effect of breaking the SU(3) symmetry, so that the interaction parameters in the spin and quadrupolar sectors are no longer equivalent, and different stages of Kondo screenings are allowed. A renormalization group analysis is used to analyze the interplay between the Kondo effect and the AFM/AFQ orders. Our work paves the way for understanding the global phase diagram in settings beyond the prototypical spin-1/2 cases. We also discuss similar considerations in the non-Kramers systems such as the heavy fermion compound PrV2Al20
Numerical simulations of heavy fermion systems. From He-3 bilayers to topological Kondo insulators
International Nuclear Information System (INIS)
Werner, Jan
2015-01-01
In this thesis the results of model calculations based on an extended Periodic Anderson Model are presented. The three particle ring exchange, which is the dominant magnetic exchange process in layered He-3, is included in the model. In addition, the model incorporates the constraint of no double occupancy by taking the limit of large local Coulomb repulsion. By means of Cellular DMFT, the model is investigated for a range of values of the chemical potential μ and inverse temperature β=1/T. The method is a cluster extension to the Dynamical Mean-Field Theory (DMFT), and allows to systematically include non-local correlations beyond the DMFT. The auxiliary cluster model is solved by a hybridization expansion CTQMC cluster solver, which provides unbiased, numerically exact results for the Green's function and other observables of interest. As a first step, the onset of Fermi liquid coherence is studied. At low enough temperature, the self-energy is found to exhibit a linear dependence on Matsubara frequency. Meanwhile, the spin susceptibility crossed over from a Curie-Weiss law to a Pauli law. The heavy fermion state appears at a characteristic coherence scale T coh . While the density is rather high for small filling, for larger filling T coh is increasingly suppressed. This involves a decreasing quasiparticle residue Z∝T coh and an enhanced mass renormalization m * /m∝T coh -1 . Extrapolation leads to a critical filling, where the coherence scale is expected to vanish at a quantum critical point. At the same time, the effective mass diverges. This corresponds to a breakdown of the Kondo effect, which is responsible for the formation of quasiparticles, due to a vanishing of the effective hybridization between the layers. Cellular DMFT simulations are conducted for small clusters of size N c =2 and 3. Furthermore a simple two-band model for two-dimensional topological Kondo insulators is devised, which is based on a single Kramer's doublet coupled to
Yamashita, Tetsuro; Miyazaki, Ryoichi; Aoki, Yuji; Ohara, Shigeo
2012-03-01
We have succeeded in synthesizing a new Yb-based Kondo lattice system, YbNi3X9 (X = Al, Ga). Our study reveals that YbNi3Al9 shows typical features of a heavy-fermion antiferromagnet with a Néel temperature of TN = 3.4 K. All of the properties reflect a competition between the Kondo effect and the crystalline electric field (CEF) effect. The moderate heavy-fermion state leads to an enhanced Sommerfeld coefficient of 100 mJ/(mol\\cdotK2), even if ordered antiferromagnetically. On the other hand, the isostructural gallide YbNi3Ga9 is an intermediate-valence system with a Kondo temperature of TK = 570 K. A large hybridization scale can overcome the CEF splitting energy, and a moderately heavy Fermi-liquid ground state with high local moment degeneracy should form at low temperatures. Note that the quality of single-crystalline YbNi3X9 is extremely high compared with those of other Yb-based Kondo lattice compounds. We conclude that YbNi3X9 is a suitable system for investigating the electronic structure of Yb-based Kondo lattice systems from a heavy-fermion system with an antiferromagnetically ordered ground state to an intermediate-valence system.
Numerical renormalization group studies of the partially brogen SU(3) Kondo model
Energy Technology Data Exchange (ETDEWEB)
Fuh Chuo, Evaristus
2013-04-15
The two-channel Kondo (2CK) effect with its exotic ground state properties has remained difficult to realize in physical systems. At low energies, a quantum impurity with orbital degree of freedom, like a proton bound in an interstitial lattice space, comprises a 3-level system with a unique ground state and (at least) doubly degenerate rotational excitations with excitation energy {Delta}{sub 0}. When immersed in a metal, electronic angular momentum scattering induces transitions between any two of these levels (couplings J), while the electron spin is conserved. We show by extensive numerical renormalization group (NRG) calculations that without fi ne-tuning of parameters this system exhibits a 2CK fixed point, due to Kondo correlations in the excited-state doublet whose degeneracy is stabilized by the host lattice parity, while the channel symmetry (electron spin) is guaranteed by time reversal symmetry. We find a pronounced plateau in the entropy at S(T{sub K}
Numerical renormalization group studies of the partially brogen SU(3) Kondo model
International Nuclear Information System (INIS)
Fuh Chuo, Evaristus
2013-04-01
The two-channel Kondo (2CK) effect with its exotic ground state properties has remained difficult to realize in physical systems. At low energies, a quantum impurity with orbital degree of freedom, like a proton bound in an interstitial lattice space, comprises a 3-level system with a unique ground state and (at least) doubly degenerate rotational excitations with excitation energy Δ 0 . When immersed in a metal, electronic angular momentum scattering induces transitions between any two of these levels (couplings J), while the electron spin is conserved. We show by extensive numerical renormalization group (NRG) calculations that without fi ne-tuning of parameters this system exhibits a 2CK fixed point, due to Kondo correlations in the excited-state doublet whose degeneracy is stabilized by the host lattice parity, while the channel symmetry (electron spin) is guaranteed by time reversal symmetry. We find a pronounced plateau in the entropy at S(T K 0 )=k B ln 2 between the high-T value, S(T>>Δ 0 )=k B ln 3, and the 2CK ground state value, S(0)=k B ln √(2). This indicates a downward renormalization of the doublet below the non-interacting ground state, thus realizing the 2CK fixed point, in agreement with earlier conjectures. We mapped out the phase diagram of the model in the J-Δ 0 plane. The Kondo temperature T K shows non-monotonic J-dependence, characteristic for 2CK systems. Beside the two-channel Kondo effect of the model, we also study the single-channel version, which is realized by applying a strong magnetic fi eld to the conduction band electrons so that their degeneracy is lifted and consequently having only one kind of electrons scattering off the impurity. This single-channel case is easier to analyze since the Hilbert space is not as large as that of the 2CK. We equally find a downward renormalization of the excited state energy by the Kondo correlations in the SU(2) doublet. In a wide range of parameter values this stabilizes the single
Test of s-wave pairing in heavy-fermion systems due to Kondo volume collapse
International Nuclear Information System (INIS)
Svozil, K.
1987-01-01
It is proposed to utilize resonant Raman scattering on heavy-fermion superconductors as a test for Cooper pairing via an effective phonon-mediated attraction due to the Kondo volume collapse. The suggested experiment might help to discriminate between singlet and triplet pairing
Antiferromagnetism and Kondo effect in a two quantum dot system: a slave boson approach
International Nuclear Information System (INIS)
Hamad, I.J.; Anda, E.V.
2012-01-01
Full text: In a recent experiment, Jakob et. al proposed a device consisting of a cobalt atom attached to the tip of a scanning tunneling microscope (STM) which interacts with another Co atom adsorbed on a gold surface. The high capacity to tune the tip-sample distance obtained by the authors, with a sub-picometre resolution, enabled the control of the electronic interaction between the two Co atoms and allowed the access to a very rich set of physical phenomena, specifically, those associated to the interplay of the antiferromagnetic interaction between the spins of the Co atoms and the Kondo correlation with the electronic reservoir spins. As well, it is possible to carefully study the geometrical aspects of the experimental disposition creating Fano anti resonances in the differential conductance as a function of the applied potential. In order to reproduce the physics observed in such an experiment we elaborate a model consisting of two sites where the electrons are highly correlated, that simulates the two Co atoms. Each atom interacts with an electronic reservoir and between themselves by means of a directed coupling and also, indirectly, through a coupling between the two electronic reservoirs. The many- body system is solved using a Slave Boson Formalism, solving the problem in the mean field approximation for finite values of U, the Coulomb electronic repulsion at the Co sites. Unlike the NRG calculations developed in the mentioned work, which partially explain the measurements, our results carries the physics information associated to the direct coupling between the Co atoms that permits to study the different regimes and the geometrical implications on the conductance results. Our study is able to explain the experimental results in all the parameter space. (author)
Numerical simulations of heavy fermion systems. From He-3 bilayers to topological Kondo insulators
Energy Technology Data Exchange (ETDEWEB)
Werner, Jan
2015-03-27
In this thesis the results of model calculations based on an extended Periodic Anderson Model are presented. The three particle ring exchange, which is the dominant magnetic exchange process in layered He-3, is included in the model. In addition, the model incorporates the constraint of no double occupancy by taking the limit of large local Coulomb repulsion. By means of Cellular DMFT, the model is investigated for a range of values of the chemical potential μ and inverse temperature β=1/T. The method is a cluster extension to the Dynamical Mean-Field Theory (DMFT), and allows to systematically include non-local correlations beyond the DMFT. The auxiliary cluster model is solved by a hybridization expansion CTQMC cluster solver, which provides unbiased, numerically exact results for the Green's function and other observables of interest. As a first step, the onset of Fermi liquid coherence is studied. At low enough temperature, the self-energy is found to exhibit a linear dependence on Matsubara frequency. Meanwhile, the spin susceptibility crossed over from a Curie-Weiss law to a Pauli law. The heavy fermion state appears at a characteristic coherence scale T{sub coh}. While the density is rather high for small filling, for larger filling T{sub coh} is increasingly suppressed. This involves a decreasing quasiparticle residue Z∝T{sub coh} and an enhanced mass renormalization m{sup *}/m∝T{sub coh}{sup -1}. Extrapolation leads to a critical filling, where the coherence scale is expected to vanish at a quantum critical point. At the same time, the effective mass diverges. This corresponds to a breakdown of the Kondo effect, which is responsible for the formation of quasiparticles, due to a vanishing of the effective hybridization between the layers. Cellular DMFT simulations are conducted for small clusters of size N{sub c}=2 and 3. Furthermore a simple two-band model for two-dimensional topological Kondo insulators is devised, which is based on a single
International Nuclear Information System (INIS)
Nguyen-Dang, T.T.; Chateauneuf, F.; Atabek, O.; He, X.
1995-01-01
The description of the wave-packet time-resolved dynamics in a two-channel molecular system driven by a cw laser field is considered within the time-independent Floquet representation. It is shown that, at high field intensity, the wave-packet motions are governed solely by the pair of adiabatic dressed potential-energy surfaces (PES's) associated with a single Brillouin zone. The same expressions of the wave-packet motions in terms of the adiabatic PES's are obtained within a short-time approximation, thereby furnishing a new numerical algorithm for the wave-packet propagation in a laser-driven two-channel system at any intensity. Numerical tests of this algorithm are presented. The numerical results establish unambiguously the adiabaticity of nuclear motions at high field intensities
Electrical resistivity of the Kondo system Ce{sub 1-x}La{sub x}Pt{sub 2}Si{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Bouziane, K.; Du Plessis, P. de V [f-Electron Magnetism and Heavy-Fermion Physics Programme, Department of Physics, University of the Witwatersrand, Private Bag 3, PO Wits 2050, Johannesburg (South Africa)
1999-04-19
The electrical resistivities of the Kondo system Ce{sub 1-x}La{sub x}Pt{sub 2}Si{sub 2} (0 {<=} x {<=} 1) are reported. It is observed that the resistivities of the alloy samples are reduced considerably as a result of annealing the samples. The results furthermore indicate the evolution from dense Kondo behaviour to single-ion incoherent Kondo scattering as x is increased. The resistivity in the dense Kondo regime shows a maximum which drops from T{sub max}=62 K for CePt{sub 2}Si{sub 2} to T{sub max}=36 K for x=0.2. Using the relationship T{sub max} {proportional_to} T{sub K} {proportional_to} exp(-1/JN(E{sub F})) where T{sub K} is the Kondo temperature, J is the exchange integral and N(E{sub F}) is the density of states at the Fermi level E{sub F}, and the experimentally observed values of T{sub max}(X) leads to vertical bar JN(E{sub F})vertical bar {sub 0} = 0.0645 {+-} 0.0004. (author)
International Nuclear Information System (INIS)
Dumoulin, Louis; Le Fur, Daniel
1976-01-01
Very low temperature superconducting tunneling experiments on CuFe(12.10 -6 ) backed by superconducting lead show a band of localized states next to the gap edge. There is no quantitative agreement with the perturbative approach of Mueller-Hartmann Zittartz in this system where the Kondo temperature is larger than the superconductive T(c) [fr
International Nuclear Information System (INIS)
Bouis, F.
1999-01-01
Two strongly correlated electron systems are considered in this work, Kondo insulators and high Tc cuprates. Experiments and theory suggest on one hand that the Kondo screening occurs on a rather short length scale and on the other hand that the Kondo coupling is renormalized to infinity in the low energy limit. The strong coupling limit is then the logical approach although the real coupling is moderate. A systematic development is performed around this limit in the first part. The band structure of these materials is reproduced within this scheme. Magnetic fluctuations are also studied. The antiferromagnetic transition is examined in the case where fermionic excitations are shifted to high energy. In the second part, the Popov and Fedotov representation of spins is used to formulate the Kondo and the antiferromagnetic Heisenberg model in terms of a non-polynomial action of boson fields. In the third part the properties of high Tc cuprates are explained by a change of topology of the Fermi surface. This phenomenon would happen near the point of optimal doping and zero temperature. It results in the appearance of a density wave phase in the under-doped regime. The possibility that this phase has a non-conventional symmetry is considered. The phase diagram that described the interaction and coexistence of density wave and superconductivity is established in the mean-field approximation. The similarities with the experimental observations are numerous in particular those concerning the pseudo-gap and the behavior of the resistivity near optimal doping. (author)
International Nuclear Information System (INIS)
Kauch, Anna; Byczuk, Krzysztof
2012-01-01
The variational local moment approach (VLMA) solution of the single impurity Anderson model is presented. It generalizes the local moment approach of Logan et al. by invoking the variational principle to determine the lengths of local moments and orbital occupancies. We show that VLMA is a comprehensive, conserving and thermodynamically consistent approximation and treats both Fermi and non-Fermi liquid regimes as well as local moment phases on equal footing. We tested VLMA on selected problems. We solved the single- and multi-orbital impurity Anderson model in various regions of parameters, where different types of Kondo effects occur. The application of VLMA as an impurity solver of the dynamical mean-field theory, used to solve the multi-orbital Hubbard model, is also addressed.
International Nuclear Information System (INIS)
Reass, W.A.; Wurden, G.A.
1997-01-01
The operational characteristics and performance of the two channel 10 Megawatt MHD feedback control system as installed by Los Alamos National Laboratory on the Columbia University HBT-EP tokamak are described. In the present configuration, driving independent 300 microH saddle coil sets, each channel can deliver 1100 Amperes and 16 kV peak to peak. Full power bandwidth is about 12 kHz, with capabilities at reduced power to 30 kHz. The present system topology is designed to suppress magnetohydrodynamic activity with m=2, n=1 symmetry. Application of either static (single phase) or rotating (twin phased) magnetic perturbations shows the ability to spin up or slow down the plasma, and also prevent (or cause) so-called ''mode-locking''. Open loop and active feedback experiments using a digital signal processor (DSP) have been performed on the HBT-EP tokamak and initial results show the ability to manipulate the plasma MHD mode frequency
Two-channel neutron boron meter
International Nuclear Information System (INIS)
Chen Yongqing; Yin Guowei; Chai Songshan; Deng Zhaoping; Zhou Bin
1993-09-01
The two-channel neutron boron meter is a continuous on-line measuring device to measure boron concentration of primary cooling liquid of reactors. The neutron-leakage-compensation method is taken in the measuring mechanism. In the primary measuring configuration, the mini-boron-water annulus and two-channel and central calibration loop are adopted. The calibration ring and constant-temperature of boron-water can be remotely controlled by secondary instruments. With the microcomputer data processing system the boron concentration is automatically measured and calibrated in on-line mode. The meter has many advantages such as high accuracy, fast response, multi-applications, high reliability and convenience
Gomez-Mendoza, M; Marin, M Luisa; Miranda, Miguel A
2014-11-14
The aim of the present work is to develop two-channel emitters to probe local hydrophobicity by means of fluorescence quenching within different biomimetic supramolecular environments. To achieve this goal, the dansyl (Dns) and tryptophan (Trp) fluorophores have been covalently attached to cholic acid (CA) in order to ensure simultaneous incorporation of the two emitting units into the same compartment. In principle, the two fluorophores of the synthesized Dns-CA-Trp probes could either exhibit an orthogonal behavior or display excited state interactions. The fluorescence spectra of 3β-Dns-CA-Trp showed a residual Trp emission band at ca. 350 nm and an enhanced Dns maximum in the 500-550 nm region. This reveals a partial intramolecular energy transfer, which is consistent with the Dns and Trp singlet energies. Thus, the two photoactive units are not orthogonal; nevertheless, 3β-Dns-CA-Trp seems appropriate as a two-channel reporter for the supramolecular systems of interest. Fluorescence quenching of 3β-Dns-CA-Trp by iodide (which remains essentially in bulk water) was examined within sodium cholate, sodium taurocholate, sodium deoxycholate and mixed micelles. Interestingly, a decrease in the emission intensity of the two bands was observed with increasing iodide concentrations. The most remarkable effect was observed for mixed micelles, where the quenching rate constants were one order of magnitude lower than in solution. As anticipated, the quenching efficiency by iodide decreased with increasing hydrophobicity of the microenvironment, a trend that can be correlated with the relative accessibility of the probe to the ionic quencher.
Energy Technology Data Exchange (ETDEWEB)
Očko, M., E-mail: ocko@ifs.hr [Institute of Physics, Bijenička c 46, 10000 Zagreb (Croatia); Center of Excellence for Advanced Materials and Sensing Devices, Ruđer Bošković Institute, Bijenička c. 54, Zagreb (Croatia); Zadro, K. [Department of Physics, University of Zagreb, Bijenička c. 32, 10000 Zagreb (Croatia); Drobac, Đ.; Aviani, I.; Salamon, K. [Institute of Physics, Bijenička c 46, 10000 Zagreb (Croatia); Mixson, D.; Bauer, E.D.; Sarrao, J.L. [Los Alamos National Laboratory, Mail Stop K 764, Los Alamos, NM 87545 (United States)
2016-11-01
In order to study Kondo ferromagnetism, particularly of the CePt compound, we investigate the magnetic properties of the Ce{sub x}La{sub 1−x}Pt alloy system in the temperature range from 1.8 K to 320 K. The results of these investigations can be summarized as follows: dc-susceptibility can be described by the Curie–Weiss law at higher temperatures down to about 100 K, but also at the low temperatures above the phase transition. At higher temperatures, the extracted Curie–Weiss constant, θ{sub p}, is negative in contrast to the low temperatures, where θ{sub C} is positive. The extracted effective magnetic moment from the higher temperatures is the same for all the alloys and is close to the theoretical value of the isolated Ce{sup 3+} ion, μ=2.54 μ{sub B}, indicating the hybridization is weak and, and consequently, Kondo interaction is weak. These observations confirm the main important conclusions inferred from an earlier transport properties investigation of this alloy system. The Curie temperature extracted by various approaches was compared to the extraction from the ac-susceptibility measurements. We show that its concentration dependence is not consistent with Doniach's diagram. Hence, RKKY interaction is not responsible for the ferromagnetism in this alloy system. - Highlights: • We have found that for Ce{sub x}La{sub 1−x}Pt the temperature of the ferromagnetic transition linearly depends on x. • The Kondo temperature is independent of x. • Hence, RKKY interaction is not responsible for the ferromagnetism. • The lattice parameters show that direct exchange interaction is possible. • We expect that the investigations of Ce{sub x}Y{sub 1−x} will confirm our conclusions.
Energy Technology Data Exchange (ETDEWEB)
Bouis, F
1999-10-14
Two strongly correlated electron systems are considered in this work, Kondo insulators and high Tc cuprates. Experiments and theory suggest on one hand that the Kondo screening occurs on a rather short length scale and on the other hand that the Kondo coupling is renormalized to infinity in the low energy limit. The strong coupling limit is then the logical approach although the real coupling is moderate. A systematic development is performed around this limit in the first part. The band structure of these materials is reproduced within this scheme. Magnetic fluctuations are also studied. The antiferromagnetic transition is examined in the case where fermionic excitations are shifted to high energy. In the second part, the Popov and Fedotov representation of spins is used to formulate the Kondo and the antiferromagnetic Heisenberg model in terms of a non-polynomial action of boson fields. In the third part the properties of high Tc cuprates are explained by a change of topology of the Fermi surface. This phenomenon would happen near the point of optimal doping and zero temperature. It results in the appearance of a density wave phase in the under-doped regime. The possibility that this phase has a non-conventional symmetry is considered. The phase diagram that described the interaction and coexistence of density wave and superconductivity is established in the mean-field approximation. The similarities with the experimental observations are numerous in particular those concerning the pseudo-gap and the behavior of the resistivity near optimal doping. (author)
The Kondo effect in ferromagnetic atomic contacts.
Calvo, M Reyes; Fernández-Rossier, Joaquín; Palacios, Juan José; Jacob, David; Natelson, Douglas; Untiedt, Carlos
2009-04-30
Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk, electronic conduction in these materials takes place mainly through the s and p electrons, whereas the magnetic moments are mostly in the narrow d-electron bands, where they tend to align. This general picture may change at the nanoscale because electrons at the surfaces of materials experience interactions that differ from those in the bulk. Here we show direct evidence for such changes: electronic transport in atomic-scale contacts of pure ferromagnets (iron, cobalt and nickel), despite their strong bulk ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of local magnetic moments by the conduction electrons below a characteristic temperature. The Kondo effect creates a sharp resonance at the Fermi energy, affecting the electrical properties of the system; this appears as a Fano-Kondo resonance in the conductance characteristics as observed in other artificial nanostructures. The study of hundreds of contacts shows material-dependent log-normal distributions of the resonance width that arise naturally from Kondo theory. These resonances broaden and disappear with increasing temperature, also as in standard Kondo systems. Our observations, supported by calculations, imply that coordination changes can significantly modify magnetism at the nanoscale. Therefore, in addition to standard micromagnetic physics, strong electronic correlations along with atomic-scale geometry need to be considered when investigating the magnetic properties of magnetic nanostructures.
Impurity quadrupole Kondo ground state in a dilute Pr system Y1-xPrxIr2Zn20
Yamane, Yu; Onimaru, Takahiro; Uenishi, Kazuto; Wakiya, Kazuhei; Matsumoto, Keisuke T.; Umeo, Kazunori; Takabatake, Toshiro
2018-05-01
The electrical resistivity ρ and specific heat C of a dilute Pr system Y1-xPrxIr2Zn20 for 0 ≤ x ≤ 0.44 were measured to study the phenomena arising from active quadrupoles of the Pr3+ ion with 4f2 configuration. On cooling, ρ's of all samples monotonically decrease, while the residual resistivity ratio ρ(300 K)/ρ(3 K) drastically decreases with x. In the whole range x ≤ 0.44, the magnetic contribution to the specific heat divided by temperature Cm/T shows a broad maximum at around 10 K, which can be reproduced by a two-level model with a first-excited triplet separated by 30 K from a ground state doublet. This indicates that the crystalline electric field ground state of the Pr ions remains in the Γ3 doublet for the cubic Td point group. On cooling, the Cm/T data for x = 0.085 and 0.44 approach constant values at Texpected from the random two-level model. By contrast, Cm/T for x = 0.044 increases continuously down to 0.08 K, suggesting a non-Fermi liquid state due to the impurity quadrupole Kondo effect.
Fano-Kondo and the Kondo box regimes crossover in a quantum dot coupled to a quantum box
Apel, Victor M.; Orellana, Pedro A.; Pacheco, Monica; Anda, Enrique V.
2013-12-01
In this work, we study the Kondo effect of a quantum dot (QD) connected to leads and to a discrete set of one-particle states provided by a quantum box represented by a quantum ring (QR) pierced by a magnetic flux side attached to the QD. The interplay between the bulk Kondo effect and the so-called Kondo box regime is studied. In this system the QR energies can be continuously modified by the application of the magnetic field. The crossover between these two regimes is analyzed by changing the connection of the QD to the QR from the weak to the strong coupling regime. In the weak coupling regime, the differential conductance develops a sequence of Fano-Kondo anti-resonances due to destructive interference between the discrete quantum ring levels and the conducting Kondo channel provided by the leads. In the strong coupling regime the differential conductance has very sharp resonances when one of the Kondo discrete sub-levels characterizing the Kondo box is tuned by the applied potential. The conductance, the current fluctuations and the Fano coefficient result as being the relevant physical magnitudes to be analyzed to reveal the physical properties of these two Kondo regimes and the crossover region between them. The results were obtained by using the slave boson mean field theory (SBMFT).
International Nuclear Information System (INIS)
Kirchner, Stefan; Si Qimiao
2009-01-01
Antiferromagnetic heavy fermion metals close to their quantum critical points display a richness in their physical properties unanticipated by the traditional approach to quantum criticality, which describes the critical properties solely in terms of fluctuations of the order parameter. This has led to the question as to how the Kondo effect gets destroyed as the system undergoes a phase change. In one approach to the problem, Kondo lattice systems are studied through a self-consistent Bose-Fermi Kondo model within the extended dynamical mean field theory. The quantum phase transition of the Kondo lattice is thus mapped onto that of a sub-Ohmic Bose-Fermi Kondo model. In the present article we address some aspects of the failure of the standard order-parameter functional for the Kondo-destroying quantum critical point of the Bose-Fermi Kondo model.
Engineering the Kondo state in two-dimensional semiconducting phosphorene
Babar, Rohit; Kabir, Mukul
2018-01-01
Correlated interaction between dilute localized impurity electrons and the itinerant host conduction electrons in metals gives rise to the conventional many-body Kondo effect below sufficiently low temperature. In sharp contrast to these conventional Kondo systems, we report an intrinsic, robust, and high-temperature Kondo state in two-dimensional semiconducting phosphorene. While absorbed at a thermodynamically stable lattice defect, Cr impurity triggers an electronic phase transition in phosphorene to provide conduction electrons, which strongly interact with the localized moment generated at the Cr site. These manifest into the intrinsic Kondo state, where the impurity moment is quenched in multiple stages and at temperatures in the 40-200 K range. Further, along with a much smaller extension of the Kondo cloud, the predicted Kondo state is shown to be robust under uniaxial strain and layer thickness, which greatly simplifies its future experimental realization. We predict the present study will open up new avenues in Kondo physics and trigger further theoretical and experimental studies.
Electron spin resonance in Yb-based Kondo-lattice systems
International Nuclear Information System (INIS)
Wykhoff, Jan
2010-01-01
The systems Yb 1-w A 1-w (Rh 1-x Co x )(Si 1-y Ge y ) 2 with A=La respectively Lu, as well as YbIr 2 Si 2 are studied. The measurements are presented sortedly for systems, dopings, and external parameters. Beside these external parameters furthermore the orientation of the sample related to the quasistatic magnetic field and the microwave magnetic field was varied.
Quantum Monte Carlo Simulation of Frustrated Kondo Lattice Models
Sato, Toshihiro; Assaad, Fakher F.; Grover, Tarun
2018-03-01
The absence of the negative sign problem in quantum Monte Carlo simulations of spin and fermion systems has different origins. World-line based algorithms for spins require positivity of matrix elements whereas auxiliary field approaches for fermions depend on symmetries such as particle-hole symmetry. For negative-sign-free spin and fermionic systems, we show that one can formulate a negative-sign-free auxiliary field quantum Monte Carlo algorithm that allows Kondo coupling of fermions with the spins. Using this general approach, we study a half-filled Kondo lattice model on the honeycomb lattice with geometric frustration. In addition to the conventional Kondo insulator and antiferromagnetically ordered phases, we find a partial Kondo screened state where spins are selectively screened so as to alleviate frustration, and the lattice rotation symmetry is broken nematically.
Kettemann, S.; Mucciolo, E. R.; Varga, I.; Slevin, K.
2012-03-01
Dilute magnetic impurities in a disordered Fermi liquid are considered close to the Anderson metal-insulator transition (AMIT). Critical power-law correlations between electron wave functions at different energies in the vicinity of the AMIT result in the formation of pseudogaps of the local density of states. Magnetic impurities can remain unscreened at such sites. We determine the density of the resulting free magnetic moments in the zero-temperature limit. While it is finite on the insulating side of the AMIT, it vanishes at the AMIT, and decays with a power law as function of the distance to the AMIT. Since the fluctuating spins of these free magnetic moments break the time-reversal symmetry of the conduction electrons, we find a shift of the AMIT, and the appearance of a semimetal phase. The distribution function of the Kondo temperature TK is derived at the AMIT, in the metallic phase, and in the insulator phase. This allows us to find the quantum phase diagram in an external magnetic field B and at finite temperature T. We calculate the resulting magnetic susceptibility, the specific heat, and the spin relaxation rate as a function of temperature. We find a phase diagram with finite-temperature transitions among insulator, critical semimetal, and metal phases. These new types of phase transitions are caused by the interplay between Kondo screening and Anderson localization, with the latter being shifted by the appearance of the temperature-dependent spin-flip scattering rate. Accordingly, we name them Kondo-Anderson transitions.
International Nuclear Information System (INIS)
Zhang Guangming; Yu Lu
2000-04-01
The ground-state phase diagram of a half-filled anisotropic Kondo lattice model is calculated within a mean-field theory. For small transverse exchange coupling J perpendicular perpendicular c1 , the ground state shows an antiferromagnetic long-range order with finite staggered magnetizations of both localized spins and conduction electrons. When J perpendicular > J perpendicular c2 , the long-range order is destroyed and the system is in a disordered Kondo singlet state with a hybridization gap. Both ground states can describe the low-temperature phases of Kondo insulating compounds. Between these two distinct phases, there may be a coexistent regime as a result of the balance between local Kondo screening and magnetic interactions. (author)
Extended Two-Channel Kondo Phase of a Rotational Quantum Defect in a Fermi Gas
International Nuclear Information System (INIS)
Chuo, E Fuh; Ballmann, K; Kroha, J; Borda, L
2014-01-01
We show by numerical renormalization group calculations that a quantum defect with a two-dimensional rotational degree of freedom, immersed in a bath of fermionic particles with angular momentum scattering, exhibits an extended 2CK phase without fine-tuning of parameters. It is stabilized by a correlation effect which causes the states with angular momentum m=±1 to be the lowest energy states of the defect. This level crossing with the noninteracting m = 0 ground state is signaled by a plateau in the temperature-dependent impurity entropy at S(T) = k_B ln 2, before the 2CK ground state value S(0) = k_B In √2 is reached.
Kondo length in bosonic lattices
Giuliano, Domenico; Sodano, Pasquale; Trombettoni, Andrea
2017-09-01
Motivated by the fact that the low-energy properties of the Kondo model can be effectively simulated in spin chains, we study the realization of the effect with bond impurities in ultracold bosonic lattices at half filling. After presenting a discussion of the effective theory and of the mapping of the bosonic chain onto a lattice spin Hamiltonian, we provide estimates for the Kondo length as a function of the parameters of the bosonic model. We point out that the Kondo length can be extracted from the integrated real-space correlation functions, which are experimentally accessible quantities in experiments with cold atoms.
Effects of pressure on doped Kondo insulators
International Nuclear Information System (INIS)
Lee, Chengchung; Xu, Wang
1999-08-01
The effects of pressure on the doped Kondo insulators (KI) are studied in the framework of the slave-boson mean-field theory under the coherent potential approximation (CPA). A unified picture for both electron-type KI and hole-type KI is presented. The density of states of the f-electrons under the applied pressures and its variation with the concentration of the Kondo holes are calculated self-consistently. The specific heat coefficient, the zero-temperature magnetic susceptibility as well as the low temperature electric resistivity of the doped KI under various pressures are obtained. The two contrasting pressure-dependent effects observed in the doped KI systems can be naturally explained within a microscopic model. (author)
International Nuclear Information System (INIS)
Fazekas, P.; Kee Haeyoung.
1993-06-01
A multi-channel generalization of Doniach's Kondo necklace model is formulated, and its phase diagram studied in the mean-field approximation. Our intention is to introduce the possible simplest model which displays some of the features expected from the overscreened Kondo lattice. The N conduction electron channels are represented by N sets of pseudospins τ J , j = 1 1,..., N which are all antiferromagnetically coupled to a periodic array of modul S = 1/2 spins. Exploiting permutation symmetry in the channel index j allows us to write down the self-consistency equation for general N. For N > 2, we find that the critical temperature is rising with increasing Kondo interaction; we interpret this effect by pointing out that the Kondo coupling creates the composite pseudospin objects which undergo an ordering transition. The relevance of our findings to the underlying fermionic multi-channel problem is discussed. (author). 33 refs, 1 fig
Energy Technology Data Exchange (ETDEWEB)
Fazekas, P; Haeyoung, Kee
1993-06-01
A multi-channel generalization of Doniach`s Kondo necklace model is formulated, and its phase diagram studied in the mean-field approximation. Our intention is to introduce the possible simplest model which displays some of the features expected from the overscreened Kondo lattice. The N conduction electron channels are represented by N sets of pseudospins {tau}{sub J}, j = 1 1,..., N which are all antiferromagnetically coupled to a periodic array of modul S = 1/2 spins. Exploiting permutation symmetry in the channel index j allows us to write down the self-consistency equation for general N. For N > 2, we find that the critical temperature is rising with increasing Kondo interaction; we interpret this effect by pointing out that the Kondo coupling creates the composite pseudospin objects which undergo an ordering transition. The relevance of our findings to the underlying fermionic multi-channel problem is discussed. (author). 33 refs, 1 fig.
Quantum phase transitions and anomalous Hall effect in a pyrochlore Kondo lattice
Grefe, Sarah; Ding, Wenxin; Si, Qimiao
The metallic variant of the pyrochlore iridates Pr2Ir2O7 has shown characteristics of a possible chiral spin liquid state [PRL 96 087204 (2006), PRL 98, 057203 (2007), Nature 463, 210 (2010)] and quantum criticality [Nat. Mater. 13, 356 (2014)]. An important question surrounding the significant anomalous Hall response observed in Pr2Ir2O7 is the nature of the f-electron local moments, including their Kondo coupling with the conduction d-electrons. The heavy effective mass and related thermodynamic characteristics indicate the involvement of the Kondo effect in this system's electronic properties. In this work, we study the effects of Kondo coupling on candidate time-reversal-symmetry-breaking spin liquid states on the pyrochlore lattice. Representing the f-moments as slave fermions Kondo-coupled to conduction electrons, we study the competition between Kondo-singlet formation and chiral spin correlations and determine the zero-temperature phase diagram. We derive an effective chiral interaction between the local moments and the conduction electrons and calculate the anomalous Hall response across the quantum phase transition from the Kondo destroyed phase to the Kondo screened phase. We discuss our results' implications for Pr2Ir2O7 and related frustrated Kondo-lattice systems.
Quantum phase transitions and anomalous Hall effect in frustrated Kondo lattices
Paschen, Silke; Grefe, Sarah Elaine; Ding, Wenxin; Si, Qimiao
Among the pyrochlore iridates, the metallic compound Pr2 Ir2O7 (Pr-227) has shown characteristics of a possible chiral spin liquid state and quantum criticality. An important question surrounding the significant anomalous Hall response observed in Pr-227 is the nature of the f-electron local moments, including their Kondo coupling with the conduction d-electrons. The heavy effective mass and related thermodynamic characteristics indicate the involvement of the Kondo effect in this system's electronic properties. In this work, we study the effects of Kondo coupling on candidate time-reversal-symmetry-breaking spin liquid states on frustrated lattices. Representing the f-moments as slave fermions Kondo-coupled to conduction electrons, we study the competition between Kondo-singlet formation and chiral spin correlations. We derive an effective chiral interaction between the local moments and the conduction electrons and calculate the anomalous Hall response across the quantum phase transition from the Kondo destroyed phase to the Kondo screened phase. We discuss our results' implications for Pr-227 and related frustrated Kondo-lattice systems.
Fermi surfaces in Kondo insulators
Liu, Hsu; Hartstein, Máté; Wallace, Gregory J.; Davies, Alexander J.; Ciomaga Hatnean, Monica; Johannes, Michelle D.; Shitsevalova, Natalya; Balakrishnan, Geetha; Sebastian, Suchitra E.
2018-04-01
We report magnetic quantum oscillations measured using torque magnetisation in the Kondo insulator YbB12 and discuss the potential origin of the underlying Fermi surface. Observed quantum oscillations as well as complementary quantities such as a finite linear specific heat capacity in YbB12 exhibit similarities with the Kondo insulator SmB6, yet also crucial differences. Small heavy Fermi sections are observed in YbB12 with similarities to the neighbouring heavy fermion semimetallic Fermi surface, in contrast to large light Fermi surface sections in SmB6 which are more similar to the conduction electron Fermi surface. A rich spectrum of theoretical models is suggested to explain the origin across different Kondo insulating families of a bulk Fermi surface potentially from novel itinerant quasiparticles that couple to magnetic fields, yet do not couple to weak DC electric fields.
Kondo and mixed-valence regimes in multilevel quantum dots
International Nuclear Information System (INIS)
Chudnovskiy, A. L.; Ulloa, S. E.
2001-01-01
We investigate the dependence of the ground state of a multilevel quantum dot on the coupling to an external fermionic system and on the interactions in the dot. As the coupling to the external system increases, the rearrangement of the effective energy levels in the dot signals the transition from the Kondo regime to a mixed-valence (MV) regime. The MV regime in a two-level dot is characterized by an intrinsic mixing of the levels in the dot, resulting in nonperturbative subtunneling and supertunneling phenomena that strongly influence the Kondo effect
Kondo effect in a deformed molecule coupled asymmetrically to ferromagnetic electrodes
International Nuclear Information System (INIS)
Rui-Qiang, Wang; Kai-Ming, Jiang
2009-01-01
The nonequilibrium Kondo effect is studied in a molecule quantum dot coupled asymmetrically to two ferromagnetic electrodes by employing the nonequilibrium Green function technique. The current-induced deformation of the molecule is taken into account, modeled as interactions with a phonon system, and phonon-assisted Kondo satellites arise on both sides of the usual main Kondo peak. In the antiparallel electrode configuration, the Kondo satellites can be split only for the asymmetric dot-lead couplings, distinguished from the parallel configuration where splitting also exists, even though it is for symmetric case. We also analyze how to compensate the splitting and restore the suppressed zero-bias Kondo resonance. It is shown that one can change the TMR ratio significantly from a negative dip to a positive peak only by slightly modulating a local external magnetic field, whose value is greatly dependent on the electron–phonon coupling strength. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Uralets, V P; Semenova, V A; Yakushin, M A; Semenov, V A
1983-11-25
A method is described for analysis of multi-component mixtures of steroid metabolites in biological fluids by means of capillary gas chromatography with glass and fused-silica columns and simultaneous detection of methoxylamine-trimethylsilyl derivatives with universal flame-ionization and selective nitrogen alkali flameionization detectors. A data system was applied to the on-line treatment of the results. Computer programs were designed for precise calculation of Kováts retention indices from the known values for selected natural urinary steroids. The programs allow the selection of nitrogen-containing components, normalized chromatogram plotting for both detection channels and qualitative and quantitative analysis. Results are presented on the detection of metabolites of methandrostenolone, 17 alpha-methyltestosterone, 19-nortestosterone and fluoxymesterone.
Two-Channel Dielectric Wake Field Accelerator
International Nuclear Information System (INIS)
Hirshfield, Jay L.
2012-01-01
Experimental results are reported for test beam acceleration and deflection in a two-channel, cm-scale, rectangular dielectric-lined wakefield accelerator structure energized by a 14-MeV drive beam. The dominant waveguide mode of the structure is at ∼30 GHz, and the structure is configured to exhibit a high transformer ratio (∼12:1). Accelerated bunches in the narrow secondary channel of the structure are continuously energized via Cherenkov radiation that is emitted by a drive bunch moving in the wider primary channel. Observed energy gains and losses, transverse deflections, and changes in the test bunch charge distribution compare favorably with predictions of theory.
A S=1 underscreened Kondo lattice model
International Nuclear Information System (INIS)
Perkins, N.B.; Nunez-Regueiro, M.D.; Iglesias, J.R.; Coqblin, B.
2006-01-01
The underscreened Kondo lattice model presented here includes both an intra-site Kondo exchange interaction J K between the conduction band and localized 5f electrons described by S=1 spins, and an inter-site exchange f-f interaction J H . We write both localized and itinerant spins in a Fermionic representation, and then use a mean-field approximation. We obtain a coexistence of Kondo effect and magnetism which can account for the behavior of some Uranium compounds
International Nuclear Information System (INIS)
Wang Ruiqiang; Jiang Kaiming
2010-01-01
We adopt the nonequilibrium Green's function method to theoretically study the Kondo effect in a deformed molecule, which is treated as an electron-phonon interaction (EPI) system. The self-energy for phonon part is calculated in the standard many-body diagrammatic expansion up to the second order in EPI strength. We find that the multiple phonon-assisted Kondo satellites arise besides the usual Kondo resonance. In the antiparallel magnetic configuration the splitting of main Kondo peak and phonon-assisted satellites only happen for asymmetrical dot-lead couplings, but it is free from the symmetry for the parallel magnetic configuration. The EPI strength and vibrational frequency can enhance the spin splitting of both main Kondo and satellites. It is shown that the suppressed zero-bias Kondo resonance can be restored by applying an external magnetic field, whose magnitude is dependent on the phononic effect remarkably. Although the asymmetry in tunnel coupling has no contribution to the restoration of spin splitting of Kondo peak, it can shrink the external field needed to switch tunneling magnetoresistance ratio between large negative dip and large positive peak. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Detecting Kondo Entanglement by Electron Conductance
Yoo, Gwangsu; Lee, S.-S. B.; Sim, H.-S.
2018-04-01
Quantum entanglement between an impurity spin and electrons nearby is a key property of the single-channel Kondo effects. We show that the entanglement can be detected by measuring electron conductance through a double quantum dot in an orbital Kondo regime. We derive a relation between the entanglement and the conductance, when the SU(2) spin symmetry of the regime is weakly broken. The relation reflects the universal form of many-body states near the Kondo fixed point. Using it, the spatial distribution of the entanglement—hence, the Kondo cloud—can be detected, with breaking of the symmetry spatially nonuniformly by electrical means.
Thermodynamics of the topological Kondo model
Directory of Open Access Journals (Sweden)
Francesco Buccheri
2015-07-01
Full Text Available Using the thermodynamic Bethe ansatz, we investigate the topological Kondo model, which describes a set of one-dimensional external wires, pertinently coupled to a central region hosting a set of Majorana bound states. After a short review of the Bethe ansatz solution, we study the system at finite temperature and derive its free energy for arbitrary (even and odd number of external wires. We then analyse the ground state energy as a function of the number of external wires and of their couplings to the Majorana bound states. Then, we compute, both for small and large temperatures, the entropy of the Majorana degrees of freedom localized within the central region and connected to the external wires. Our exact computation of the impurity entropy provides evidence of the importance of fermion parity symmetry in the realization of the topological Kondo model. Finally, we also obtain the low-temperature behaviour of the specific heat of the Majorana bound states, which provides a signature of the non-Fermi-liquid nature of the strongly coupled fixed point.
Thermodynamics of the topological Kondo model
Energy Technology Data Exchange (ETDEWEB)
Buccheri, Francesco, E-mail: buccheri@iip.ufrn.br [International Institute of Physics, Universidade Federal do Rio Grande do Norte, 59078-400 Natal, RN (Brazil); Babujian, Hrachya [International Institute of Physics, Universidade Federal do Rio Grande do Norte, 59078-400 Natal, RN (Brazil); Yerevan Physics Institute, Alikhanian Brothers 2, Yerevan, 375036 (Armenia); Korepin, Vladimir E. [International Institute of Physics, Universidade Federal do Rio Grande do Norte, 59078-400 Natal, RN (Brazil); C. N. Yang Institute for Theoretical Physics, Stony Brook University, NY 11794 (United States); Sodano, Pasquale [International Institute of Physics, Universidade Federal do Rio Grande do Norte, 59078-400 Natal, RN (Brazil); Departemento de Fisíca Teorica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, RN (Brazil); Trombettoni, Andrea [CNR-IOM DEMOCRITOS Simulation Center, Via Bonomea 265, I-34136 Trieste (Italy); SISSA and INFN, Sezione di Trieste, Via Bonomea 265, I-34136 Trieste (Italy)
2015-07-15
Using the thermodynamic Bethe ansatz, we investigate the topological Kondo model, which describes a set of one-dimensional external wires, pertinently coupled to a central region hosting a set of Majorana bound states. After a short review of the Bethe ansatz solution, we study the system at finite temperature and derive its free energy for arbitrary (even and odd) number of external wires. We then analyse the ground state energy as a function of the number of external wires and of their couplings to the Majorana bound states. Then, we compute, both for small and large temperatures, the entropy of the Majorana degrees of freedom localized within the central region and connected to the external wires. Our exact computation of the impurity entropy provides evidence of the importance of fermion parity symmetry in the realization of the topological Kondo model. Finally, we also obtain the low-temperature behaviour of the specific heat of the Majorana bound states, which provides a signature of the non-Fermi-liquid nature of the strongly coupled fixed point.
Devil's staircase in Kondo semimetals
International Nuclear Information System (INIS)
Ueda, K.; Shibata, N.; Science Univ. of Tokyo; Ishii, C.
1996-01-01
Complex magnetic phase diagrams of the trivalent cerium monopnictides are widely known as an example of the devil's staircase. We present an effective Hamiltonian for CeX which explains their complex magnetic phase diagrams in a unified way. The effective Hamiltonian consists of semimetallic conduction bands and localized f spins. A new feature is the inter-band transitions with spin exchange which frustrates with the usual intra-band Kondo couplings. (orig.)
Prediction of femtosecond oscillations in the transient current of a quantum dot in the Kondo regime
Goker, A.; Manchon, Aurelien; Schwingenschlö gl, Udo; Zhu, Zhiyong
2010-01-01
of a gate voltage. For an asymmetrically coupled system, we observe that the instantaneous conductance in the Kondo time scale exhibits beating with distinct frequencies, which are proportional to the separation between the Fermi level and the sharp
The Kondo effect of an adatom in graphene and its scanning tunneling spectroscopy
International Nuclear Information System (INIS)
Li Lin; Ni Yangyang; Zhong Yin; Fang Tiefeng; Luo Honggang
2013-01-01
We study the Kondo effect of a single magnetic adatom on the surface of graphene. The unique linear dispersion relation near the Dirac points in graphene makes it easier for the magnetic atom to form a local magnetic moment, which simply means that the Kondo resonance can be observed in a wider parameter region than in the metallic host. Our study indicates that the Kondo resonance, whenever the chemical potential is tuned away from the Dirac points, can indeed occur ranging from the Kondo regime, to the mixed valence, even to the empty orbital regime defined in the conventional metal host. While the Kondo resonance appears as a sharp peak in the Kondo regime, it has a peak-dip structure and/or an anti-resonance in the mixed valence and empty orbital regimes, which result from the Fano resonance due to the significant background due to dramatic broadening of the impurity level in graphene. We also study the scanning tunneling microscopy (STM) spectra of the adatom and they show obvious particle–hole asymmetry when the chemical potential is tuned by the gate voltages applied to the graphene. Finally, we explore the influence of the direct tunneling channel between the STM tip and the graphene on the Kondo resonance and find that the lineshape of the Kondo resonance is unaffected, which can be attributed to an unusually large asymmetry factor in graphene. Our study indicates that graphene is an ideal platform to systematically study Kondo physics and these results are useful to further stimulate relevant experimental studies on the system. (paper)
Prats, J. M.; Lopez-Aguilar, F.
1996-01-01
Using unitary transformations, we express the Kondo lattice Hamiltonian in terms of fermionic operators that annihilate the ground state of the interacting system and that represent the best possible approximations to the actual charged excitations. In this way, we obtain an effective Hamiltonian which, for small couplings, consists in a kinetic term for conduction electrons and holes, an RKKY-like term, and a renormalized Kondo interaction. The physical picture of the system implied by this ...
The Kondo temperature of a two-dimensional electron gas with Rashba spin–orbit coupling
International Nuclear Information System (INIS)
Chen, Liang; Lin, Hai-Qing; Sun, Jinhua; Tang, Ho-Kin
2016-01-01
We use the Hirsch–Fye quantum Monte Carlo method to study the single magnetic impurity problem in a two-dimensional electron gas with Rashba spin–orbit coupling. We calculate the spin susceptibility for various values of spin–orbit coupling, Hubbard interaction, and chemical potential. The Kondo temperatures for different parameters are estimated by fitting the universal curves of spin susceptibility. We find that the Kondo temperature is almost a linear function of Rashba spin–orbit energy when the chemical potential is close to the edge of the conduction band. When the chemical potential is far away from the band edge, the Kondo temperature is independent of the spin–orbit coupling. These results demonstrate that, for single impurity problems in this system, the most important reason to change the Kondo temperature is the divergence of density of states near the band edge, and the divergence is induced by the Rashba spin–orbit coupling. (paper)
Thermoelectric Phenomena in a Quantum Dot Attached to Ferromagnetic Leads in Kondo Regime
International Nuclear Information System (INIS)
Chen Qiao; Zhao Li-Li
2014-01-01
We have studied the thermoelectric properties through ferromagnetic leads-QD coupled system (F-QD-F) in the Kondo regime by nonequilibrium Green's functions method. The spin-flip effect induced by ferromagnetic leads and Kondo effect influence the thermoelectric properties significantly. The peak-valley structure emerges at the low temperature due to Kondo resonance, and the peak-valley structure also relies on the polarization angle θ, the spin-dependent linewidth function Γ γσ and the energy level of QD ∈ d . Novel resonant peak also emerges in the curve of ZT c versus polarization angle θ. The Kondo effect suppresses the figure of merit ZT c and the spin-dependent figure of merit ZT s . In addition, the spin-dependent figure of merit ZT s is relate with the gap between Γ γ↑ and Γ γ↓ . (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Two-Channel Transparency-Optimized Control Architectures in Bilateral Teleoperation With Time Delay.
Kim, Jonghyun; Chang, Pyung Hun; Park, Hyung-Soon
2013-01-01
This paper introduces transparency-optimized control architectures (TOCAs) using two communication channels. Two classes of two-channel TOCAs are found, thereby showing that two channels are sufficient to achieve transparency. These TOCAs achieve a greater level of transparency but poorer stability than three-channel TOCAs and four-channel TOCAs. Stability of the two-channel TOCAs has been enhanced while minimizing transparency degradation by adding a filter; and a combined use of the two classes of two-channel TOCAs is proposed for both free space and constrained motion, which involve switching between two TOCAs for transition between free space and constrained motions. The stability condition of the switched teleoperation system is derived for practical applications. Through the one degree-of-freedom (DOF) experiment, the proposed two-channel TOCAs were shown to operate stably, while achieving better transparency under time delay than the other TOCAs.
Two-Channel Transparency-Optimized Control Architectures in Bilateral Teleoperation With Time Delay
Kim, Jonghyun; Chang, Pyung Hun; Park, Hyung-Soon
2013-01-01
This paper introduces transparency-optimized control architectures (TOCAs) using two communication channels. Two classes of two-channel TOCAs are found, thereby showing that two channels are sufficient to achieve transparency. These TOCAs achieve a greater level of transparency but poorer stability than three-channel TOCAs and four-channel TOCAs. Stability of the two-channel TOCAs has been enhanced while minimizing transparency degradation by adding a filter; and a combined use of the two classes of two-channel TOCAs is proposed for both free space and constrained motion, which involve switching between two TOCAs for transition between free space and constrained motions. The stability condition of the switched teleoperation system is derived for practical applications. Through the one degree-of-freedom (DOF) experiment, the proposed two-channel TOCAs were shown to operate stably, while achieving better transparency under time delay than the other TOCAs. PMID:23833548
Two-color Fermi-liquid theory for transport through a multilevel Kondo impurity
Karki, D. B.; Mora, Christophe; von Delft, Jan; Kiselev, Mikhail N.
2018-05-01
We consider a quantum dot with K ≥2 orbital levels occupied by two electrons connected to two electric terminals. The generic model is given by a multilevel Anderson Hamiltonian. The weak-coupling theory at the particle-hole symmetric point is governed by a two-channel S =1 Kondo model characterized by intrinsic channels asymmetry. Based on a conformal field theory approach we derived an effective Hamiltonian at a strong-coupling fixed point. The Hamiltonian capturing the low-energy physics of a two-stage Kondo screening represents the quantum impurity by a two-color local Fermi liquid. Using nonequilibrium (Keldysh) perturbation theory around the strong-coupling fixed point we analyze the transport properties of the model at finite temperature, Zeeman magnetic field, and source-drain voltage applied across the quantum dot. We compute the Fermi-liquid transport constants and discuss different universality classes associated with emergent symmetries.
Fano–Kondo Effect in a Triple Quantum Dots Coupled to Ferromagnetic Leads
International Nuclear Information System (INIS)
Ai-Hua, Bi; Shao-Quan, Wu; Tao, Hou; Wei-Li, Sun
2008-01-01
Using the Keldysh nonequilibrium Green function and equation-of-motion technique, we have qualitatively studied the spin-dependent transport of a triple-QD system in the Kondo regime. It is shown that the Kondo resonance and Fano interference coexist, and in this system the Fano–Kondo effect shows dip behaviours richer than that in the T-shaped QDs. The interdot coupling, the energy level of the side coupled QDs and the spin polarization strength greatly influence the DOS of the central quantum dot QD 0 . Either the increase of the coupling strength between the two QDs or that of the energy levels of the side coupled QDs enhances the Kondo resonance. Especially, the Kondo resonance is strengthened greatly when the side dot energy is fixed at the Fermi energy. Meanwhile, the Kondo resonance splits for the spin-up and spin-down configurations due to the polarization: the down-spin resonance is enhanced, and the up-spin resonance is suppressed. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Energy Technology Data Exchange (ETDEWEB)
Wykhoff, Jan
2010-07-07
The systems Yb{sub 1-w}A{sub 1-w}(Rh{sub 1-x}Co{sub x})(Si{sub 1-y}Ge{sub y}){sub 2} with A=La respectively Lu, as well as YbIr{sub 2}Si{sub 2} are studied. The measurements are presented sortedly for systems, dopings, and external parameters. Beside these external parameters furthermore the orientation of the sample related to the quasistatic magnetic field and the microwave magnetic field was varied.
Quantum quenches in a holographic Kondo model
Erdmenger, Johanna; Flory, Mario; Newrzella, Max-Niklas; Strydom, Migael; Wu, Jackson M. S.
2017-04-01
We study non-equilibrium dynamics and quantum quenches in a recent gauge/gravity duality model for a strongly coupled system interacting with a magnetic impurity with SU( N ) spin. At large N , it is convenient to write the impurity spin as a bilinear in Abrikosov fermions. The model describes an RG flow triggered by the marginally relevant Kondo operator. There is a phase transition at a critical temperature, below which an operator condenses which involves both an electron and an Abrikosov fermion field. This corresponds to a holographic superconductor in AdS2 and models the impurity screening. We quench the Kondo coupling either by a Gaussian pulse or by a hyperbolic tangent, the latter taking the system from the condensed to the uncondensed phase or vice-versa. We study the time dependence of the condensate induced by this quench. The timescale for equilibration is generically given by the leading quasinormal mode of the dual gravity model. This mode also governs the formation of the screening cloud, which is obtained as the decrease of impurity degrees of freedom with time. In the condensed phase, the leading quasinormal mode is imaginary and the relaxation of the condensate is over-damped. For quenches whose final state is close to the critical point of the large N phase transition, we study the critical slowing down and obtain the combination of critical exponents zν = 1. When the final state is exactly at the phase transition, we find that the exponential ringing of the quasinormal modes is replaced by a power-law behaviour of the form ˜ t - a sin( b log t). This indicates the emergence of a discrete scale invariance.
Quantum quenches in a holographic Kondo model
Energy Technology Data Exchange (ETDEWEB)
Erdmenger, Johanna [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut),Föhringer Ring 6, 80805, Munich (Germany); Institut für Theoretische Physik und Astrophysik, Julius-Maximilians-Universität Würzburg,Am Hubland, 97074 Würzburg (Germany); Flory, Mario [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut),Föhringer Ring 6, 80805, Munich (Germany); Institute of Physics, Jagiellonian University,Łojasiewicza 11, 30-348 Kraków (Poland); Newrzella, Max-Niklas; Strydom, Migael [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut),Föhringer Ring 6, 80805, Munich (Germany); Wu, Jackson M. S. [Department of Physics and Astronomy, University of Alabama,Tuscaloosa, AL 35487 (United States)
2017-04-10
We study non-equilibrium dynamics and quantum quenches in a recent gauge/ gravity duality model for a strongly coupled system interacting with a magnetic impurity with SU(N) spin. At large N, it is convenient to write the impurity spin as a bilinear in Abrikosov fermions. The model describes an RG flow triggered by the marginally relevant Kondo operator. There is a phase transition at a critical temperature, below which an operator condenses which involves both an electron and an Abrikosov fermion field. This corresponds to a holographic superconductor in AdS{sub 2} and models the impurity screening. We quench the Kondo coupling either by a Gaussian pulse or by a hyperbolic tangent, the latter taking the system from the condensed to the uncondensed phase or vice-versa. We study the time dependence of the condensate induced by this quench. The timescale for equilibration is generically given by the leading quasinormal mode of the dual gravity model. This mode also governs the formation of the screening cloud, which is obtained as the decrease of impurity degrees of freedom with time. In the condensed phase, the leading quasinormal mode is imaginary and the relaxation of the condensate is over-damped. For quenches whose final state is close to the critical point of the large N phase transition, we study the critical slowing down and obtain the combination of critical exponents zν=1. When the final state is exactly at the phase transition, we find that the exponential ringing of the quasinormal modes is replaced by a power-law behaviour of the form ∼t{sup −a}sin (blog t). This indicates the emergence of a discrete scale invariance.
Phase diagram of the Kondo-Heisenberg model on honeycomb lattice with geometrical frustration
Li, Huan; Song, Hai-Feng; Liu, Yu
2016-11-01
We calculated the phase diagram of the Kondo-Heisenberg model on a two-dimensional honeycomb lattice with both nearest-neighbor and next-nearest-neighbor antiferromagnetic spin exchanges, to investigate the interplay between RKKY and Kondo interactions in the presence of magnetic frustration. Within a mean-field decoupling technology in slave-fermion representation, we derived the zero-temperature phase diagram as a function of Kondo coupling J k and frustration strength Q. The geometrical frustration can destroy the magnetic order, driving the original antiferromagnetic (AF) phase to non-magnetic valence bond solids (VBS). In addition, we found two distinct VBS. As J k is increased, a phase transition from AF to Kondo paramagnetic (KP) phase occurs, without the intermediate phase coexisting AF order with Kondo screening found in square lattice systems. In the KP phase, the enhancement of frustration weakens the Kondo screening effect, resulting in a phase transition from KP to VBS. We also found a process to recover the AF order from VBS by increasing J k in a wide range of frustration strength. Our work may provide predictions for future experimental observation of new processes of quantum phase transitions in frustrated heavy-fermion compounds.
Interplay between Kondo and Majorana Interactions in Quantum Dots
Directory of Open Access Journals (Sweden)
Meng Cheng
2014-09-01
Full Text Available We study the properties of a quantum dot coupled to a topological superconductor and a normal lead and discuss the interplay between Kondo-and Majorana-induced couplings in quantum dots. The latter appears due to the presence of Majorana zero-energy modes localized, for example, at the ends of the one-dimensional superconductor. We investigate the phase diagram of the system as a function of Kondo and Majorana interactions using a renormalization-group analysis, a slave-boson mean-field theory, and numerical simulations using the density-matrix renormalization-group method. We show that, in addition to the well-known Kondo fixed point, the system may flow to a new fixed point controlled by the Majorana-induced coupling, which is characterized by nontrivial correlations between a localized spin on the dot and the fermion parity of the topological superconductor and the normal lead. We compute several measurable quantities, such as differential tunneling conductance and impurity-spin susceptibility, which highlight some peculiar features characteristic to the Majorana fixed point.
Quantum quench of Kondo correlations in optical absorption.
Latta, C; Haupt, F; Hanl, M; Weichselbaum, A; Claassen, M; Wuester, W; Fallahi, P; Faelt, S; Glazman, L; von Delft, J; Türeci, H E; Imamoglu, A
2011-06-29
The interaction between a single confined spin and the spins of an electron reservoir leads to one of the most remarkable phenomena of many-body physics--the Kondo effect. Electronic transport measurements on single artificial atoms, or quantum dots, have made it possible to study the effect in great detail. Here we report optical measurements on a single semiconductor quantum dot tunnel-coupled to a degenerate electron gas which show that absorption of a single photon leads to an abrupt change in the system Hamiltonian and a quantum quench of Kondo correlations. By inferring the characteristic power-law exponents from the experimental absorption line shapes, we find a unique signature of the quench in the form of an Anderson orthogonality catastrophe, induced by a vanishing overlap between the initial and final many-body wavefunctions. We show that the power-law exponent that determines the degree of orthogonality can be tuned using an external magnetic field, which unequivocally demonstrates that the observed absorption line shape originates from Kondo correlations. Our experiments demonstrate that optical measurements on single artificial atoms offer new perspectives on many-body phenomena previously studied using transport spectroscopy only.
Spin-1 two-impurity Kondo problem on a lattice
Allerdt, A.; Žitko, R.; Feiguin, A. E.
2018-01-01
We present an extensive study of the two-impurity Kondo problem for spin-1 adatoms on a square lattice using an exact canonical transformation to map the problem onto an effective one-dimensional system that can be numerically solved using the density matrix renormalization group method. We provide a simple intuitive picture and identify the different regimes, depending on the distance between the two impurities, Kondo coupling JK, longitudinal anisotropy D , and transverse anisotropy E . In the isotropic case, two impurities on opposite (the same) sublattices have a singlet (triplet) ground state. However, the energy difference between the triplet ground state and the singlet excited state is very small and we expect an effectively fourfold-degenerate ground state, i.e., two decoupled impurities. For large enough JK the impurities are practically uncorrelated forming two independent underscreened states with the conduction electrons, a clear nonperturbative effect. When the impurities are entangled in an RKKY-like state, Kondo correlations persist and the two effects coexist: the impurities are underscreened, and the dangling spin-1 /2 degrees of freedom are responsible for the interimpurity entanglement. We analyze the effects of magnetic anisotropy in the development of quasiclassical correlations.
Kondo peak splitting and Kondo dip in single molecular magnet junctions
Energy Technology Data Exchange (ETDEWEB)
Niu, Pengbin, E-mail: 120233951@qq.com [Institute of Solid State Physics, Shanxi Datong University, Datong 037009 (China); Shi, Yunlong; Sun, Zhu [Institute of Solid State Physics, Shanxi Datong University, Datong 037009 (China); Nie, Yi-Hang [Institute of Theoretical Physics, Shanxi University, Taiyuan 030006 (China); Luo, Hong-Gang [Center for Interdisciplinary Studies & Key Laboratory for Magnetism and Magnetic Materials of the MoE, Lanzhou University, Lanzhou 730000 (China); Beijing Computational Science Research Center, Beijing 100084 (China)
2016-01-15
Many factors containing bias, spin–orbit coupling, magnetic fields applied, and so on can strongly influence the Kondo effect, and one of the consequences is Kondo peak splitting (KPS). It is natural that KPS should also appear when another spin degree of freedom is involved. In this work we study the KPS effects of single molecular magnets (SMM) coupled with two metallic leads in low-temperature regime. It is found that the Kondo transport properties are strongly influenced by the exchange coupling and anisotropy of the magnetic core. By employing Green's function method in Hubbard operator representation, we give an analytical expression for local retarded Green's function of SMM and discussed its low-temperature transport properties. We find that the anisotropy term behaves as a magnetic field and the splitting behavior of exchange coupling is quite similar to the spin–orbit coupling. These splitting behaviors are explained by introducing inter-level or intra-level transitions, which account for the seven-peak splitting structure. Moreover, we find a Kondo dip at Fermi level under proper parameters. These Kondo peak splitting behaviors in SMM deepen our understanding to Kondo physics and should be observed in the future experiments. - Highlights: • We study Kondo peak splitting in single molecular magnets. • We study Kondo effect by Hubbard operator Green's function method. • We find Kondo peak splitting structures and a Kondo dip at Fermi level. • The exchange coupling and magnetic anisotropy induce fine splitting structure. • The splitting structures are explained by inter-level or intra-level transitions.
Frustrated quantum magnetism in the Kondo lattice on the zigzag ladder
Peschke, Matthias; Rausch, Roman; Potthoff, Michael
2018-03-01
The interplay between the Kondo effect, indirect magnetic interaction, and geometrical frustration is studied in the Kondo lattice on the one-dimensional zigzag ladder. Using the density-matrix renormalization group, the ground-state and various short- and long-range spin- and density-correlation functions are calculated for the model at half filling as a function of the antiferromagnetic Kondo interaction down to J =0.3 t , where t is the nearest-neighbor hopping on the zigzag ladder. Geometrical frustration is shown to lead to at least two critical points: Starting from the strong-J limit, where almost local Kondo screening dominates and where the system is a nonmagnetic Kondo insulator, antiferromagnetic correlations between nearest-neighbor and next-nearest-neighbor local spins become stronger and stronger, until at Jcdim≈0.89 t frustration is alleviated by a spontaneous breaking of translational symmetry and a corresponding transition to a dimerized state. This is characterized by antiferromagnetic correlations along the legs and by alternating antiferro- and ferromagnetic correlations on the rungs of the ladder. A mechanism of partial Kondo screening that has been suggested for the Kondo lattice on the two-dimensional triangular lattice is not realized in the one-dimensional case. Furthermore, within the symmetry-broken dimerized state, there is a magnetic transition to a 90∘ quantum spin spiral with quasi-long-range order at Jcmag≈0.84 t . The quantum-critical point is characterized by a closure of the spin gap (with decreasing J ) and a divergence of the spin-correlation length and of the spin-structure factor S (q ) at wave vector q =π /2 . This is opposed to the model on the one-dimensional bipartite chain, which is known to have a finite spin gap for all J >0 at half filling.
Filling-enforced nonsymmorphic Kondo semimetals in two dimensions
Pixley, J. H.; Lee, SungBin; Brandom, B.; Parameswaran, S. A.
2017-08-01
We study the competition between Kondo screening and frustrated magnetism on the nonsymmorphic Shastry-Sutherland Kondo lattice at a filling of two conduction electrons per unit cell. This model is known to host a set of gapless partially Kondo screened phases intermediate between the Kondo-destroyed paramagnet and the heavy Fermi liquid. Based on crystal symmetries, we argue that (i) both the paramagnet and the heavy Fermi liquid are semimetals protected by a glide symmetry; and (ii) partial Kondo screening breaks the symmetry, removing this protection and allowing the partially Kondo screened phase to be deformed into a Kondo insulator via a Lifshitz transition. We confirm these results using large-N mean-field theory and then use nonperturbative arguments to derive a generalized Luttinger sum rule constraining the phase structure of two-dimensional nonsymmorphic Kondo lattices beyond the mean-field limit.
From Kondo to local singlet state in graphene nanoribbons with magnetic impurities
Diniz, G. S.; Luiz, G. I.; Latgé, A.; Vernek, E.
2018-03-01
A detailed analysis of the Kondo effect of a magnetic impurity in a zigzag graphene nanoribbon is addressed. An adatom is coupled to the graphene nanoribbon via a hybridization amplitude Γimp in a hollow- or top-site configuration. In addition, the adatom is also weakly coupled to a metallic scanning tunnel microscope (STM) tip by a hybridization function Γtip that provides a Kondo screening of its magnetic moment. The entire system is described by an Anderson-like Hamiltonian whose low-temperature physics is accessed by employing the numerical renormalization-group approach, which allows us to obtain the thermodynamic properties used to compute the Kondo temperature of the system. We find two screening regimes when the adatom is close to the edge of the zigzag graphene nanoribbon: (1) a weak-coupling regime (Γimp≪Γtip ), in which the edge states produce an enhancement of the Kondo temperature TK, and (2) a strong-coupling regime (Γimp≫Γtip ), in which a local singlet is formed, to the detriment of the Kondo screening by the STM tip. These two regimes can be clearly distinguished by the dependence of their characteristic temperature T* on the coupling between the adatom and the carbon sites of the graphene nanoribbon Vimp. We observe that in the weak-coupling regime T* increases exponentially with Vimp2. Differently, in the strong-coupling regime, T* increases linearly with Vimp2.
Two channel EEG thought pattern classifier.
Craig, D A; Nguyen, H T; Burchey, H A
2006-01-01
This paper presents a real-time electro-encephalogram (EEG) identification system with the goal of achieving hands free control. With two EEG electrodes placed on the scalp of the user, EEG signals are amplified and digitised directly using a ProComp+ encoder and transferred to the host computer through the RS232 interface. Using a real-time multilayer neural network, the actual classification for the control of a powered wheelchair has a very fast response. It can detect changes in the user's thought pattern in 1 second. Using only two EEG electrodes at positions O(1) and C(4) the system can classify three mental commands (forward, left and right) with an accuracy of more than 79 %
Lateral spin-orbit coupling and the Kondo effect in quantum dots
Vernek, Edson; Ngo, Anh; Ulloa, Sergio
2010-03-01
We present studies of the Coulomb blockade and Kondo regimes of transport of a quantum dot connected to current leads through spin-polarizing quantum point contacts (QPCs) [1]. This configuration, arising from the effect of lateral spin-orbit fields, results in spin-polarized currents even in the absence of external magnetic fields and greatly affects the correlations in the dot. Using an equation-of-motion technique and numerical renormalization group calculations we obtain the conductance and spin polarization for this system under different parameter regimes. Our results show that both the Coulomb blockade and Kondo regimes exhibit non-zero spin-polarized conductance. We analyze the role that the spin-dependent tunneling amplitudes of the QPC play in determining the charge and net magnetic moment in the dot. We find that the Kondo regime exhibits a strongly dependent Kondo temperature on the QPC polarizability. These effects, controllable by lateral gate voltages, may provide a new approach for exploring Kondo correlations, as well as possible spin devices. Supported by NSF DMR-MWN and PIRE. [1] P. Debray et al., Nature Nanotech. 4, 759 (2009).
Sapkota, Keshab R.; Maloney, F. Scott; Wang, Wenyong
2018-04-01
In this work, we report unusual observations of Kondo effect and coexistence of Kondo effect and ferromagnetism in indium tin oxide (ITO) nanowires that were synthesized without incorporating any magnetic impurities. The temperature-dependent resistivity (ρ -T ) data exhibited an upturn below 80 K and then tended to saturate below 10 K. The ρ -T and magnetoresistance data were analyzed using the n -channel Kondo model, and from the obtained values of S =1 and n ˜1 , the nanowires were expected to be an underscreened Kondo system. A model was also proposed to explain the formation of localized S =1 spin centers in the ITO nanowires. This work could provide insights into the understanding of spin-related novel phenomena in metal oxide nanostructures.
Prediction of femtosecond oscillations in the transient current of a quantum dot in the Kondo regime
Goker, A.
2010-10-11
We invoke the time-dependent noncrossing approximation in order to study the effects of the density of states of gold contacts on the instantaneous conductance of a single electron transistor which is abruptly moved into the Kondo regime by means of a gate voltage. For an asymmetrically coupled system, we observe that the instantaneous conductance in the Kondo time scale exhibits beating with distinct frequencies, which are proportional to the separation between the Fermi level and the sharp features in the density of states of gold. Increasing the ambient temperature or bias quenches the amplitude of the oscillations. We attribute the oscillations to interference between the emerging Kondo resonance and van-Hove singularities in the density of state. In addition, we propose an experimental realization of this model.
Exploring the anisotropic Kondo model in and out of equilibrium with alkaline-earth atoms
Kanász-Nagy, Márton; Ashida, Yuto; Shi, Tao; Moca, Cǎtǎlin Paşcu; Ikeda, Tatsuhiko N.; Fölling, Simon; Cirac, J. Ignacio; Zaránd, Gergely; Demler, Eugene A.
2018-04-01
We propose a scheme to realize the Kondo model with tunable anisotropy using alkaline-earth atoms in an optical lattice. The new feature of our setup is Floquet engineering of interactions using time-dependent Zeeman shifts, that can be realized either using state-dependent optical Stark shifts or magnetic fields. The properties of the resulting Kondo model strongly depend on the anisotropy of the ferromagnetic interactions. In particular, easy-plane couplings give rise to Kondo singlet formation even though microscopic interactions are all ferromagnetic. We discuss both equilibrium and dynamical properties of the system that can be measured with ultracold atoms, including the impurity spin susceptibility, the impurity spin relaxation rate, as well as the equilibrium and dynamical spin correlations between the impurity and the ferromagnetic bath atoms. We analyze the nonequilibrium time evolution of the system using a variational non-Gaussian approach, which allows us to explore coherent dynamics over both short and long timescales, as set by the bandwidth and the Kondo singlet formation, respectively. In the quench-type experiments, when the Kondo interaction is suddenly switched on, we find that real-time dynamics shows crossovers reminiscent of poor man's renormalization group flow used to describe equilibrium systems. For bare easy-plane ferromagnetic couplings, this allows us to follow the formation of the Kondo screening cloud as the dynamics crosses over from ferromagnetic to antiferromagnetic behavior. On the other side of the phase diagram, our scheme makes it possible to measure quantum corrections to the well-known Korringa law describing the temperature dependence of the impurity spin relaxation rate. Theoretical results discussed in our paper can be measured using currently available experimental techniques.
Anomalously suppressed localization in the two-channel Anderson model
International Nuclear Information System (INIS)
Nguyen, Ba Phi; Kim, Kihong
2012-01-01
We study numerically the localization properties of a two-channel quasi-one-dimensional Anderson model with uncorrelated diagonal disorder within the nearest-neighbor tight-binding approximation. We calculate and analyze the disorder-averaged transmittance and the Lyapunov exponent. We find that the localization of the entire system is enhanced by increasing the interchain hopping strength t-tilde. From the numerical investigation of the energy dependence of the Lyapunov exponent for many different interchain hopping strengths, we find that apart from the band center anomaly, which usually occurs in strictly one-dimensional disordered systems, additional anomalies appear at special spectral points. They are found to be associated with the interchain hopping strength and occur at E=± t-tilde/2 and ± t-tilde. We find that the anomalies at E=± t-tilde are associated with the π-coupling occurring within one energy band and those at E=± t-tilde/2 are associated with the π-coupling occurring between two different energy bands. Despite having a similar origin, these two anomalies have distinct characteristics in their dependence on the strength of disorder. We also show that for a suitable range of parameter values, effectively delocalized states are observed in finite-size systems. (paper)
The ferromagnetic Kondo-lattice compound SmFe sub 4 P sub 1 sub 2
Takeda, N
2003-01-01
We report on the magnetic properties of a filled skutterudite compound, SmFe sub 4 P sub 1 sub 2. Magnetic susceptibility and specific heat measurements revealed a ferromagnetic transition at 1.6 K. The temperature dependence of the electrical resistivity exhibits a Kondo-lattice behaviour and the electronic specific heat coefficient attains values as large as 370 mJ mol sup - sup 1 K sup - sup 2. This compound is thereby the first Sm-based heavy-fermion system found with a ferromagnetic ground state. The Kondo temperature is estimated to be about 30 K. (letter to the editor)
Kondo effect and non-Fermi liquid behavior in metallic glasses containing Yb, Ce, and Sm
Huang, B.; Yang, Y. F.; Wang, W. H.
2013-04-01
The low temperature properties of metallic glasses containing different concentrations of ytterbium, cerium, and samarium are studied. It is found that the Kondo effect caused by exchange interactions between the conduction and 4f electrons and non-Fermi liquid behavior appear in the strongly disordered alloys. We study the origins for these unique features and demonstrate that the found Kondo effect is inherited from the crystalline counterparts. The results might have significance on investigating the strong electron-electron interaction systems with structural disorder and be helpful for designing new metallic glasses with functional properties.
International Nuclear Information System (INIS)
Nishiyama, Shinya; Matsuura, Hiroyasu; Miyake, Kazumasa
2011-01-01
In f 2 -based heavy fermion systems with a tetragonal symmetry, we investigate the magnetic field dependence of a non-fermi liquid (NFL) which arises related to the quantum critical point (QCP) due to the competition between the crystalline-electric field (CEF) singlet and the Kondo-Yosida singlet states. On the basis of the Wilson numerical renormalization group method, we find that the magnetic field less than a characteristic magnetic field H z * does not affect the characteristic temperature T F * at which the specific heat takes a maximum value. Since such H z * increases as the deviation from the QCP increases, slightly off the QCP, there are parameter regions where NFL behaviors are robust at an observable temperature range T > T F *against a magnetic field of up to H z * which is far larger than T F *. Our result suggests that such robust NFL behaviors can arise also in systems with other CEF symmetries; e.g., magnetically robust NFL behaviors observed in UBe 13 may be understood on this basis.
Importance of conduction electron correlation in a Kondo lattice, Ce₂CoSi₃.
Patil, Swapnil; Pandey, Sudhir K; Medicherla, V R R; Singh, R S; Bindu, R; Sampathkumaran, E V; Maiti, Kalobaran
2010-06-30
Kondo systems are usually described by the interaction of the correlation induced local moments with the highly itinerant conduction electrons. Here, we study the role of electron correlations among conduction electrons in the electronic structure of a Kondo lattice compound, Ce₂CoSi₃, using high resolution photoemission spectroscopy and ab initio band structure calculations, where Co 3d electrons contribute in the conduction band. High energy resolution employed in the measurements helped to reveal the signatures of Ce 4f states derived Kondo resonance features at the Fermi level and the dominance of Co 3d contributions at higher binding energies in the conduction band. The lineshape of the experimental Co 3d band is found to be significantly different from that obtained from the band structure calculations within the local density approximations, LDA. Consideration of electron-electron Coulomb repulsion, U, among Co 3d electrons within the LDA + U method leads to a better representation of experimental results. The signature of an electron correlation induced satellite feature is also observed in the Co 2p core level spectrum. These results clearly demonstrate the importance of the electron correlation among conduction electrons in deriving the microscopic description of such Kondo systems.
Temperature-Independent Fermi Surface in the Kondo Lattice YbRh_{2}Si_{2}
Directory of Open Access Journals (Sweden)
K. Kummer
2015-03-01
Full Text Available Strongly correlated electron systems are one of the central topics in contemporary solid-state physics. Prominent examples for such systems are Kondo lattices, i.e., intermetallic materials in which below a critical temperature, the Kondo temperature T_{K}, the magnetic moments become quenched and the effective masses of the conduction electrons approach the mass of a proton. In Ce- and Yb-based systems, this so-called heavy-fermion behavior is caused by interactions between the strongly localized 4f and itinerant electrons. A major and very controversially discussed issue in this context is how the localized electronic degree of freedom gets involved in the Fermi surface (FS upon increasing the interaction between both kinds of electrons or upon changing the temperature. In this paper, we show that the FS of a prototypic Kondo lattice, YbRh_{2}Si_{2}, does not change its size or shape in a wide temperature range extending from well below to far above the single-ion Kondo temperature T_{K}∼25 K of this system. This experimental observation, obtained by means of angle-resolved photoemission spectroscopy, is in remarkable contrast to the widely believed evolution from a large FS, including the 4f degrees of freedom, to a small FS, without the 4f’s, upon increasing temperature. Our results explicitly demonstrate a need to further advance in theoretical approaches based on the periodic Anderson model in order to elucidate the temperature dependence of Fermi surfaces in Kondo lattices.
Nonequilibrium Floquet States in Topological Kondo Insulators
2016-02-04
approximately 200 mW of power (given ~5 ohm sample Figure 2: Longitudinal resistance measured in SmB6 crystal with simultaneous ultrasound ...Research Triangle Park, NC 27709-2211 floquet Kondo topological ultrasound REPORT DOCUMENTATION PAGE 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 10...observation of a positive effect. Further work is required to understand the origin of the anomalous effect of ultrasound propagation on electrical
CePdAl. A frustrated Kondo lattice at a quantum critical point
Energy Technology Data Exchange (ETDEWEB)
Fritsch, Veronika [EP 6, Electronic Correlations and Magnetism, University of Augsburg (Germany); Karlsruhe Institute of Technology (Germany); Sakai, Akito; Gegenwart, Philipp [EP 6, Electronic Correlations and Magnetism, University of Augsburg (Germany); Huesges, Zita; Lucas, Stefan; Stockert, Oliver [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Kittler, Wolfram; Taubenheim, Christian; Grube, Kai; Loehneysen, Hilbert von [Karlsruhe Institute of Technology (Germany); Huang, Chien-Lung [Karlsruhe Institute of Technology (Germany); Max Planck Institute for Chemical Physics of Solids, Dresden (Germany)
2016-07-01
CePdAl is one of the rare frustrated Kondo lattice systems that can be tuned across a quantum critical point (QCP) by means of chemical pressure, i. e., the substitution of Pd by Ni. Magnetic frustration and Kondo effect are antithetic phenomena: The Kondo effect with the incipient delocalization of the magnetic moments, is not beneficial for the formation of a frustrated state. On the other hand, magnetic frustrated exchange interactions between the local moments can result in a breakdown of Kondo screening. Furthermore, the fate of frustration is unclear when approaching the QCP, since there is no simple observable to quantify the degree of frustration. We present thermodynamic and neutron scattering experiments on CePd{sub 1-x}Ni{sub x}Al close to the critical concentration x ∼0.14. Our experiments indicate that even at the QCP magnetic frustration is still present, opening the perspective to find new universality classes at such a quantum phase transition.
SU(4) Kondo effect in double quantum dots with ferromagnetic leads
Weymann, Ireneusz; Chirla, Razvan; Trocha, Piotr; Moca, Cǎtǎlin Paşcu
2018-02-01
We investigate the spin-resolved transport properties, such as the linear conductance and the tunnel magnetoresistance, of a double quantum dot device attached to ferromagnetic leads and look for signatures of the SU (4 ) symmetry in the Kondo regime. We show that the transport behavior greatly depends on the magnetic configuration of the device, and the spin-SU(2) as well as the orbital and spin-SU(4) Kondo effects become generally suppressed when the magnetic configuration of the leads varies from the antiparallel to the parallel one. Furthermore, a finite spin polarization of the leads lifts the spin degeneracy and drives the system from the SU(4) to an orbital-SU(2) Kondo state. We analyze in detail the crossover and show that the Kondo temperature between the two fixed points has a nonmonotonic dependence on the degree of spin polarization of the leads. In terms of methods used, we characterize transport by using a combination of analytical and numerical renormalization group approaches.
Negativity as the Entanglement Measure to Probe the Kondo Regime in the Spin-Chain Kondo Model
Bayat, Abolfazl; Sodano, Pasquale; Bose, Sougato
2009-01-01
We study the entanglement of an impurity at one end of a spin chain with a block of spins using negativity as a true measure of entanglement to characterize the unique features of the gapless Kondo regime in the spin chain Kondo model. For this spin chain in the Kondo regime we determine- with a true entanglement measure- the spatial extent of the Kondo screening cloud, we propose an ansatz for its ground state and demonstrate that the impurity spin is indeed maximally entangled with the clou...
International Nuclear Information System (INIS)
Dino, Wilson Agerico; Kasai, Hideaki; Rodulfo, Emmanuel Tapas; Nishi, Mayuko
2006-01-01
Manifestations of the Kondo effect on an atomic length scale on and around a magnetic atom adsorbed on a nonmagnetic surface differ depending on the spectroscopic mode of operation of the scanning tunneling microscope. Two prominent signatures of the Kondo effect that can be observed at surfaces are the development of a sharp resonance (Yosida-Kondo resonance) at the Fermi level, which broadens with increasing temperature, and the splitting of this sharp resonance upon application of an external magnetic field. Until recently, observing the temperature and magnetic field dependence has been a challenge, because the experimental conditions strongly depend on the system's critical temperature, the so-called Kondo temperature T K . In order to clearly observe the temperature dependence, one needs to choose a system with a large T K . One can thus perform the experiments at temperatures T K . However, because the applied external magnetic field necessary to observe the magnetic field dependence scales with T K , one needs to choose a system with a very small T K . This in turn means that one should perform the experiments at very low temperatures, e.g., in the mK range. Here we discuss the temperature and magnetic field dependence of the Yosida-Kondo resonance for a single magnetic atom on a metal surface, in relation to recent experimental developments
A Two-Channel Training Algorithm for Hidden Markov Model and Its Application to Lip Reading
Directory of Open Access Journals (Sweden)
Foo Say Wei
2005-01-01
Full Text Available Hidden Markov model (HMM has been a popular mathematical approach for sequence classification such as speech recognition since 1980s. In this paper, a novel two-channel training strategy is proposed for discriminative training of HMM. For the proposed training strategy, a novel separable-distance function that measures the difference between a pair of training samples is adopted as the criterion function. The symbol emission matrix of an HMM is split into two channels: a static channel to maintain the validity of the HMM and a dynamic channel that is modified to maximize the separable distance. The parameters of the two-channel HMM are estimated by iterative application of expectation-maximization (EM operations. As an example of the application of the novel approach, a hierarchical speaker-dependent visual speech recognition system is trained using the two-channel HMMs. Results of experiments on identifying a group of confusable visemes indicate that the proposed approach is able to increase the recognition accuracy by an average of 20% compared with the conventional HMMs that are trained with the Baum-Welch estimation.
Siegert pseudostate formulation of scattering theory: two-channel case
Sitnikov, G V
2003-01-01
Siegert pseudostates (SPS) are a finite basis representation of Siegert states (SS) for finite-range potentials. This paper presents a generalization of the SPS formulation of scattering theory, originally developed by Tolstikhin, Ostrovsky, and Nakamura ÝPhys. Rev. A 58, 2077 (1998)¿ for s-wave scattering in the one-channel case, to s-wave scattering in the two-channel case. This includes the investigation of the properties of orthogonality and completeness of two-channel SPS and the derivation of the SPS expansions for the two- channel Green function, wave function, and scattering matrix. Similar to the one-channel case, two types of expansions for the scattering matrix are obtained: one has a form of a sum and requires the knowledge of both the SPS eigenvalues and eigenfunctions, while the other has a form of a product and involves the eigenvalues only. As the size of the basis tends to infinity, the product formulas obtained here in terms of SPS coincide with those given by Le Couteur ÝProc. R. Soc. Lo...
Site dependence of the Kondo scale in CePd{sub 1-x}Rh{sub x} evidenced by thermopower
Energy Technology Data Exchange (ETDEWEB)
Stockert, Ulrike; Hartmann, Stefanie; Deppe, Micha; Caroca-Canales, Nubia; Geibel, Christoph; Steglich, Frank [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Sereni, Julian [Division Bajas Temperaturas, Centro Atomico Bariloche (Argentina)
2015-07-01
CePd{sub 1-x}Rh{sub x} undergoes a continuous evolution from ferromagnetic order in CePd to an intermediate-valence (IV) ground state for CeRh. Close to the disappearance of magnetic order at x{sub cr} ∼ 0.87 unusual behavior of the ac susceptibility and the specific heat was observed. It was explained with a broad distribution of local Kondo temperatures T{sub K} from below 2 K to above 50 K due to the disorder introduced by Pd-Rh exchange. The thermopower S is very sensitive to Kondo scattering even for diluted 4f systems. In Ce compounds a large positive maximum in S(T) is usually observed around T{sub K}. We studied S(T) in CePd{sub 1-x}Rh{sub x} in order to evaluate the presence of Kondo scattering and the involved energy scales. Pure CeRh shows typical IV behavior with a large maximum at 220 K and small values at low T. Already 5 % Pd substitution leads to a strong enhancement of the low-T thermopower. Even larger values are found around x{sub cr}, while the high-T maximum shifts only moderately. Our results are in line with the existence of low (local) Kondo scales in the presence of IV behavior at high Rh content x > x{sub cr}. For lower Rh content a decreasing (average) Kondo scale is found.
Nanomechanical dissipation at a tip-induced Kondo onset
Baruselli, Pier Paolo; Fabrizio, Michele; Tosatti, Erio
2017-08-01
The onset or demise of Kondo effect in a magnetic impurity on a metal surface can be triggered, as sometimes observed, by the simple mechanical nudging of a tip. Such a mechanically driven quantum phase transition must reflect in a corresponding mechanical dissipation peak; yet, this kind of signature has not been focused upon so far. Aiming at the simplest theoretical modeling, we treat the impurity as an Anderson impurity model, the tip action as a hybridization switching, and solve the problem by numerical renormalization group. Studying this model as function of temperature and magnetic field we are able to isolate the Kondo contribution to dissipation. While that is, reasonably, of the order of the Kondo energy, its temperature evolution shows a surprisingly large tail even above the Kondo temperature. The detectability of Kondo mechanical dissipation in atomic force microscopy is also discussed.
Studies on Kondo insulating FeSi
International Nuclear Information System (INIS)
Bharathi, A.; Mani, Awadhesh; Ravindran, Nithya; Mathi Jaya, S.; Sundar, C.S.; Hariharan, Y.
2000-01-01
Temperature dependent electrical resistivity measurements have been carried out in Fe (1-x) Ru x Si and FeSi (1-x) Ge x to examine the robustness of the Kondo Insulating gap to substitution in the Fe and Si sublattices. The gap is seen to decrease with Ge substitution, while for Ru substitution the gap shows an initial decrease followed by an increase at higher concentration. The results can be understood in terms of the shift in the mobility edge due to disorder and/or pressure effects in combination with changes in band structure
Vibrationally inelastic electron scattering in a two-channel approximation
Czech Academy of Sciences Publication Activity Database
Čársky, Petr; Čurík, Roman
2008-01-01
Roč. 41, č. 5 (2008), , , 055203-1-6 ISSN 0953-4075 R&D Projects: GA AV ČR IAA100400501; GA AV ČR 1ET400400413; GA AV ČR KJB400400803; GA ČR GA202/08/0631; GA MŠk ME 857 Institutional research plan: CEZ:AV0Z40400503 Keywords : inelastic electron scattering * two-channel approximation Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.089, year: 2008
Correlated evolution of colossal thermoelectric effect and Kondo insulating behavior
Directory of Open Access Journals (Sweden)
M. K. Fuccillo
2013-12-01
Full Text Available We report the magnetic and transport properties of the Ru1−xFexSb2 solid solution, showing how the colossal thermoelectric performance of FeSb2 evolves due to changes in the amount of 3d vs. 4d electron character. The physical property trends shed light on the physical picture underlying one of the best low-T thermoelectric power factors known to date. Some of the compositions warrant further study as possible n- and p-type thermoelements for Peltier cooling well below 300 K. Our findings enable us to suggest possible new Kondo insulating systems that might behave similarly to FeSb2 as advanced thermoelectrics.
Collective Kondo effect in the Anderson-Hubbard lattice
Fazekas, P.; Itai, K.
1997-02-01
The periodic Anderson model is extended by switching on a Hubbard U for the conduction electrons. We use the Gutzwiller variational method to study the nearly integral valent limit. The lattice Kondo energy contains the U-dependent chemical potential of the Hubbard subsystem in the exponent, and the correlation-induced band narrowing in the prefactor. Both effects tend to suppress the Kondo scale, which can be understood to result from the blocking of hybridization. At half-filling, we find a Brinkman-Rice-type transition from a Kondo insulator to a Mott insulator.
Correlated mean filed Ansatz for the Kondo necklace
International Nuclear Information System (INIS)
Kee, H.Y.; Fazekas, P.
1993-08-01
We study the ground state phase diagram of the pseudospin model introduced by Doniach to describe the essential physics of Kondo lattices. We use variational trial states which augment the usual mean field solution by incorporating various intersite correlations. A composite spin correlation describing the antiparallel alignment of fluctuating triplets is found to be particularly favourable for large Kondo couplings. With this trial state, the magnetic-to-Kondo transition is suppressed and the strong coupling ground state is ordered with strongly reduced moments. The relevance of the findings is discussed. (author). 19 refs, 4 figs
Kondo effect and heavy fermions in Yb compounds
International Nuclear Information System (INIS)
Bonville, P.
1987-01-01
The Kondo properties of Yb dilute alloys and intermetallics have been investigated using Moessbauer spectroscopy on 170 Yb. In the dilute alloys AuYb and LaBe 13 Yb, the Kondo logarithmic anomaly of the impurity relaxation rate has been detected, and in the concentrated Yb compounds YbBe 13 , YbP and YbAs, and YbCuAl, the manifestations of the interplay between the Kondo effect and the magnetic ordering due to the RKKY interaction have been characterized
Correlated mean filed Ansatz for the Kondo necklace
Energy Technology Data Exchange (ETDEWEB)
Kee, H Y; Fazekas, P
1993-08-01
We study the ground state phase diagram of the pseudospin model introduced by Doniach to describe the essential physics of Kondo lattices. We use variational trial states which augment the usual mean field solution by incorporating various intersite correlations. A composite spin correlation describing the antiparallel alignment of fluctuating triplets is found to be particularly favourable for large Kondo couplings. With this trial state, the magnetic-to-Kondo transition is suppressed and the strong coupling ground state is ordered with strongly reduced moments. The relevance of the findings is discussed. (author). 19 refs, 4 figs.
Heavy Fermion Materials and Quantum Phase Transitions Workshop on Frontiers of the Kondo Effect
2016-02-12
SECURITY CLASSIFICATION OF: The contemporary studies of the Kondo effect and heavy -fermion materials occur at the intersection of some of the most...magnetism. Electronic systems in this intermediate regime are particularly tunable. Correspondingly, heavy fermions have emerged as a promising setting...materials. Second, heavy -fermion materials typically contain heavy elements, and there is an increasing 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND
COAXIAL TWO-CHANNEL DIELECTRIC WAKE FIELD ACCELERATOR
Energy Technology Data Exchange (ETDEWEB)
Hirshfield, Jay L. [Omega-P, Inc.
2013-04-30
Theory, computations, and experimental apparatus are presented that describe and are intended to confirm novel properties of a coaxial two-channel dielectric wake field accelerator. In this configuration, an annular drive beam in the outer coaxial channel excites multimode wakefields which, in the inner channel, can accelerate a test beam to an energy much higher than the energy of the drive beam. This high transformer ratio is the result of judicious choice of the dielectric structure parameters, and of the phase separation between drive bunches and test bunches. A structure with cm-scale wakefields has been build for tests at the Argonne Wakefield Accelerator Laboratory, and a structure with mm-scale wakefields has been built for tests at the SLAC FACET facility. Both tests await scheduling by the respective facilities.
Interaction quench dynamics in the Kondo model in the presence of a local magnetic field.
Heyl, M; Kehrein, S
2010-09-01
In this work we investigate the quench dynamics in the Kondo model on the Toulouse line in the presence of a local magnetic field. It is shown that this setup can be realized by either applying the local magnetic field directly or by preparing the system in a macroscopically spin-polarized initial state. In the latter case, the magnetic field results from a subtlety in applying the bosonization technique where terms that are usually referred to as finite-size corrections become important in the present non-equilibrium setting. The transient dynamics are studied by analyzing exact analytical results for the local spin dynamics. The timescale for the relaxation of the local dynamical quantities turns out to be exclusively determined by the Kondo scale. In the transient regime, one observes damped oscillations in the local correlation functions with a frequency set by the magnetic field.
Tunable quantum criticality and super-ballistic transport in a "charge" Kondo circuit.
Iftikhar, Z; Anthore, A; Mitchell, A K; Parmentier, F D; Gennser, U; Ouerghi, A; Cavanna, A; Mora, C; Simon, P; Pierre, F
2018-05-03
Quantum phase transitions (QPTs) are ubiquitous in strongly-correlated materials. However the microscopic complexity of these systems impedes the quantitative understanding of QPTs. Here, we observe and thoroughly analyze the rich strongly-correlated physics in two profoundly dissimilar regimes of quantum criticality. With a circuit implementing a quantum simulator for the three-channel Kondo model, we reveal the universal scalings toward different low-temperature fixed points and along the multiple crossovers from quantum criticality. Notably, an unanticipated violation of the maximum conductance for ballistic free electrons is uncovered. The present charge pseudospin implementation of a Kondo impurity opens access to a broad variety of strongly-correlated phenomena. Copyright © 2018, American Association for the Advancement of Science.
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...
Kondo effect in single-molecule magnet transistors
Gonzalez, Gabriel; Leuenberger, Michael; Mucciolo, Eduardo
2009-03-01
We present a careful and thorough microscopic derivation of the anisotropic Kondo Hamiltonian for single-molecule magnet (SMM) transistors. When the molecule is strongly coupled to metallic leads, we show that by applying a transverse magnetic field it is possible to topologically induce or quench the Kondo effect in the conductance of a SMM with either an integer or a half-integer spin S>1/2. This topological Kondo effect is due to the Berry-phase interference between multiple quantum tunneling paths of the spin. We calculate the renormalized Berry-phase oscillations of the two Kondo peaks as a function of a transverse magnetic field by means of the poor man's scaling approach. We illustrate our findings with the SMM Ni4, which we propose as a possible candidate for the experimental observation of the conductance oscillations.
Energy Technology Data Exchange (ETDEWEB)
Gruner, T.; Caroca-Canales, N.; Deppe, M.; Geibel, C. [MPI fuer Chemische Physik fester Stoffe, 01187, Dresden (Germany); Sereni, J. [Centro Atomico Bariloche, 8400, S. C. de Bariloche (Argentina)
2011-07-01
CeTiGe is a paramagnetic Kondo lattice system with a large orbital degeneracy involved in the formation of the heavy Fermion ground state. Recently we discovered that this compound presents a huge metamagnetic transition at B{sub MMT} {approx} 13 T, with much larger anomalies in magnetization, magnetoresistance and magnetostriction than in the archetypical Kondo lattice metamagnet CeRu{sub 2}Si{sub 2}. Since CeTiGe forms in a pronounced peritectic reaction the growth of single crystals is difficult. We therefore studied the Ce-Ti-Ge ternary metallographic phase diagram to get a sound basis for future crystal growth attempts. Preliminary results of growth experiments based on these studies are promising and shall be discussed. Furthermore, Ti-rich CeTiGe was recently reported to present a high temperature phase crystallizing in the closely related CeScSi structure type. In order to study this structural instability and the effect on the physical properties, we studied the effect of substituting Sc for Ti, since pure CeScGe crystallizes in the CeScSi structure type. In well annealed samples we observed a two phase region in the range 10% - 25%-Sc-substitution. Preliminary investigations of the CeSc{sub x}Ti{sub 1-x}Ge alloy suggest it is a promising candidate for the observation of a ferromagnetic quantum critical point in a large degeneracy Kondo lattice system.
Angle-resolved photoemission on the Kondo surface alloy CePd{sub 7}
Energy Technology Data Exchange (ETDEWEB)
Mulazzi, Mattia; Seibel, Christoph; Schwab, Holger [Universitaet Wuerzburg, Experimentelle Physik VII (Germany); Shimada, Kenya; Jiang, Jiang [Graduate School of Science, Hiroshima University, Higashi-Hiroshima (Japan); Reinert, Friedrich [Universitaet Wuerzburg, Experimentelle Physik VII (Germany); Karlsruhe Institute of Technology KIT, Gemeinschaftslabor fuer Nanoanalytik, Karlsruhe (Germany)
2013-07-01
This films of the Cerium were evaporated on a Pd(001) substrate an further annealed to obtain a thin surface alloy layer of stoichiometry CePd{sub 7}, as observed by Auger spectroscopy. From LEED measurements it was possible to determine that the alloy has a (√(5) x √(5))R26.6 {sup circle} reconstruction, commensurate to the Palladium substrate. Photon-energy dependent ARPES measurements crossing the 4d-4f resonance show the presence of a strong peak near the Fermi level, having actually two components, the actual Kondo peak at the Fermi level and the spin-orbit peak at 280 meV binding energy. Resonant and non-resonant Fermi surface maps shows large intensity variations of the Pd bands, when measured at the resonance, a sign of strong hybridization between the conduction and the 4f electrons. While previous work assigns the CePd7 to the class of intermediate valence systems, our work shows that it is actually a Kondo system, with a rather high Kondo temperature.
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.
Directory of Open Access Journals (Sweden)
R Nourafkan
2009-08-01
Full Text Available It is a common knowledge that the formation of electron pairs is a necessary ingredient of any theoretical work describing superconductivity. Thus, finding the mechanism of the formation of the electron pairs is of utmost importance. There are some experiments on high transition temperature superconductors which support the electron-phonon (e-ph interactions as the pairing mechanism (ARPES, and there are others which support the spin fluctuations as their pairing mechanism (tunneling spectroscopy. In this paper, we introduce the Holstein-Kondo lattice model (H-KLM which incorporates the e-ph as well as the Kondo exchange interaction. We have used the dynamical mean field theory (DMFT to describe heavy fermion semiconductors and have employed the exact-diagonalization technique to obtain our results. The phase diagram of these systems in the parameter space of the e-ph coupling, g, and the Kondo exchange coupling, J, show that the system can be found in the Kondo insulating phase, metallic phase or the bi-polaronic phase. It is shown that these systems develop both spin gap and a charge gap, which are different and possess energies in the range of 1-100 meV. In view of the fact that both spin excitation energies and phonon energies lie in this range, we expect our work on H-KLM opens a way to formalize the theory of the high transition temperature superconductors .
Troć, R.; Gajek, Z.; Pikul, A.; Misiorek, H.; Colineau, E.; Wastin, F.
2013-07-01
The transport properties described previously [Troć , Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.85.224434 85, 224434 (2012)] as well as the magnetic and thermal properties presented in this paper, observed for single-crystalline UCu2Si2, are discussed by assuming a dual (localized-itinerant) scenario. The electronic states of the localized 5f electrons in UCu2Si2 are constructed using the effective Hamiltonian known for ionic systems, allowing us to treat the Coulomb, spin-orbital, and crystal-field interactions on equal footing. The space of parameters has been restricted in the initial steps with the aid of the angular overlap model approximation. The final crystal-field parameters, obtained from the refined steps of calculations, are relatively large (in absolute values), which we attribute to the hybridization characteristic of the metallic systems on the verge of localization. The proposed crystal-field model reproduces correctly with satisfactory accuracy the magnetic and thermal properties of UCu2Si2 in agreement also with the transport properties reported previously. Considerable crystal-field splitting of the ground multiplet of 2760 K is responsible for a large anisotropy in the magnetic behavior, observed in the whole temperature range explored.
Hybridization in Kondo lattice heavy fermions via quasiparticle scattering spectroscopy (QPS)
Narasiwodeyar, Sanjay; Dwyer, Matt; Greene, Laura; Park, Wan Kyu; Bauer, Eric; Tobash, Paul; Baumbach, Ryan; Ronning, Filip; Sarrao, John; Thompson, Joe; Canfield, Paul
2014-03-01
Band renormalization in a Kondo lattice via hybridization of the conduction band with localized states has been a hot topic over the last several years. In part, this has to do with recently reignited interest in the hidden order problem in URu2Si2. Despite recent developments regarding the electronic structure in this compound, it remains to be resolved whether the hidden order phase transition is related to the opening of a hybridization gap. Our quasiparticle scattering spectroscopy (QPS) has shown they are not related directly. This can be understood naturally since in principle band renormalization does not involve symmetry breaking. To deepen our understanding, we extend to other Kondo lattice compounds. For instance, when applied to YbAl3, a vegetable heavy-fermion system, QPS reveals conductance signatures for hybridization in a Kondo lattice such as asymmetric Fano background along with characteristic energy scales. Presenting new results on these materials, we will discuss a broader picture. The work at UIUC is supported by the NSF DMR 12-06766, the work at LANL is carried out under the auspices of the U.S. DOE, Office of Science, and the work done at Ames Lab. was supported under Contract No. DE-AC02-07CH11358.
Green's function approach to the Kondo effect in nanosized quantum corrals
Li, Q. L.; Wang, R.; Xie, K. X.; Li, X. X.; Zheng, C.; Cao, R. X.; Miao, B. F.; Sun, L.; Wang, B. G.; Ding, H. F.
2018-04-01
We present a theoretical study of the Kondo effect for a magnetic atom placed inside nanocorrals using Green's function calculations. Based on the standard mapping of the Anderson impurity model to a one-dimensional chain model, we formulate a weak-coupling theory to study the Anderson impurities in a hosting bath with a surface state. With further taking into account the multiple scattering effect of the surrounding atoms, our calculations show that the Kondo resonance width of the atom placed at the center of the nanocorral can be significantly tuned by the corral size, in good agreement with recent experiments [Q. L. Li et al., Phys. Rev. B 97, 035417 (2018), 10.1103/PhysRevB.97.035417]. The method can also be applied to the atom placed at an arbitrary position inside the corral where our calculation shows that the Kondo resonance width also oscillates as the function of its separation from the corral center. The prediction is further confirmed by the low-temperature scanning tunneling microscopy studies where a one-to-one correspondence is found. The good agreement with the experiments validates the generality of the method to the system where multiadatoms are involved.
Spin relaxation and the Kondo effect in transition metal dichalcogenide monolayers
International Nuclear Information System (INIS)
Rostami, Habib; Moghaddam, Ali G; Asgari, Reza
2016-01-01
We investigate the spin relaxation and Kondo resistivity caused by magnetic impurities in doped transition metal dichalcogenide monolayers. We show that momentum and spin relaxation times, due to the exchange interaction by magnetic impurities, are much longer when the Fermi level is inside the spin-split region of the valence band. In contrast to the spin relaxation, we find that the dependence of Kondo temperature T K on the doping is not strongly affected by the spin–orbit induced splitting, although only one of the spin species are present at each valley. This result, which is obtained using both perturbation theory and the poor man’s scaling methods, originates from the intervalley spin-flip scattering in the spin-split region. We further demonstrate the decline in the conductivity with temperatures close to T K , which can vary with the doping. Our findings reveal the qualitative difference with the Kondo physics in conventional metallic systems and other Dirac materials. (paper)
Phonon-assisted Kondo effect in single-molecule quantum dots coupled to ferromagnetic leads
International Nuclear Information System (INIS)
Yu Hui; Wen Tingdun; Liang, J.-Q.; Sun, Q.F.
2008-01-01
Based on the infinite-U Anderson model spin-polarized transport through the tunnel magnetoresistance (TMR) system of single-molecule quantum dot is investigated under the interplay of strong electron correlation and electron-phonon (e-ph) coupling. The spectral density and the nonlinear differential conductance are studied using the extended non-equilibrium Green's function method through calculating the dot-level splitting self-consistently. The results exhibit that a serial of peaks emerge on the two sides of the main Kondo peak for the antiparallel magnetic configuration of electrodes, while for the parallel case both the main and phonon-assisted satellite Kondo peaks all split up into two asymmetric peaks even at zero-bias. Correspondingly, the nonlinear differential conductance displays a set of satellite-peaks around the Kondo-peak in the presence of the e-ph interaction. Furthermore, extra maxima and minima appear in the TMR curve. The TMR alternates between the positive and the negative values along with the variation of bias voltage
Two-Channel Metal Detector Using Two Perpendicular Antennas
Directory of Open Access Journals (Sweden)
Kyoo Nam Choi
2014-01-01
Full Text Available Two-channel metal detector, having two sets of perpendicularly oriented sensor antennas, is proposed to expand detectable size, ranging from mm through cm scale, of metal sensor, while conventional metal sensor is dedicated for detection only in mm or cm scale. The characteristics of the two metal detection sensor channels were investigated, respectively, and the interference effect, while in simultaneous operation, between two sensor channels was discussed. Metal detection channel, having sensitivity in mm scale, showed detectable sensitivity to moving ferrous sphere, with diameter down to 0.7 mm, at 50 kHz exciting frequency and enhanced sensitivity distribution. And metal detection channel having sensitivity in cm scale showed more uniform sensitivity distribution with the flexibility for future modular construction. The effect of interference, while in simultaneous operation of two sensors, resulted in reduced output response, but still within usable detection range. Thus it was feasible to operate two sensors, having different sensitivity range, simultaneously and to extend detection range from mm to cm scale, within practically acceptable interference.
MAGMA: analysis of two-channel microarrays made easy.
Rehrauer, Hubert; Zoller, Stefan; Schlapbach, Ralph
2007-07-01
The web application MAGMA provides a simple and intuitive interface to identify differentially expressed genes from two-channel microarray data. While the underlying algorithms are not superior to those of similar web applications, MAGMA is particularly user friendly and can be used without prior training. The user interface guides the novice user through the most typical microarray analysis workflow consisting of data upload, annotation, normalization and statistical analysis. It automatically generates R-scripts that document MAGMA's entire data processing steps, thereby allowing the user to regenerate all results in his local R installation. The implementation of MAGMA follows the model-view-controller design pattern that strictly separates the R-based statistical data processing, the web-representation and the application logic. This modular design makes the application flexible and easily extendible by experts in one of the fields: statistical microarray analysis, web design or software development. State-of-the-art Java Server Faces technology was used to generate the web interface and to perform user input processing. MAGMA's object-oriented modular framework makes it easily extendible and applicable to other fields and demonstrates that modern Java technology is also suitable for rather small and concise academic projects. MAGMA is freely available at www.magma-fgcz.uzh.ch.
Kondo Impurities Coupled to a Helical Luttinger Liquid: RKKY-Kondo Physics Revisited.
Yevtushenko, Oleg M; Yudson, Vladimir I
2018-04-06
We show that the paradigmatic Ruderman-Kittel-Kasuya-Yosida (RKKY) description of two local magnetic moments coupled to propagating electrons breaks down in helical Luttinger liquids when the electron interaction is stronger than some critical value. In this novel regime, the Kondo effect overwhelms the RKKY interaction over all macroscopic interimpurity distances. This phenomenon is a direct consequence of the helicity (realized, for instance, at edges of a time-reversal invariant topological insulator) and does not take place in usual (nonhelical) Luttinger liquids.
Fano-Andreev effect in Quantum Dots in Kondo regime
Orellana, Pedro; Calle, Ana Maria; Pacheco, Monica; Apel, Victor
In the present work, we investigate the transport through a T-shaped double quantum dot system coupled to two normal leads and to a superconducting lead. We study the role of the superconducting lead in the quantum interferometric features of the double quantum dot and by means of a slave boson mean field approximation at low temperature regime. We inquire into the influence of intradot interactions in the electronic properties of the system as well. Our results show that Fano resonances due to Andreev bound states are exhibited in the transmission from normal to normal lead as a consequence of quantum interference and proximity effect. This Fano effect produced by Andreev bound states in a side quantum dot was called Fano-Andreev effect, which remains valid even if the electron-electron interaction are taken into account, that is, the Fano-Andreev effect is robust against e-e interactions even in Kondo regime. We acknowledge the financial support from FONDECYT program Grants No. 3140053 and 11400571.
Two stages of Kondo effect and competition between RKKY and Kondo in Gd-based intermetallic compound
Energy Technology Data Exchange (ETDEWEB)
Vaezzadeh, Mehdi [Department of Physics, K.N.Toosi University of Technology, P.O. Box 15875-4416, Tehran (Iran, Islamic Republic of)]. E-mail: mehdi@kntu.ac.ir; Yazdani, Ahmad [Tarbiat Modares University, P.O. Box 14155-4838, Tehran (Iran, Islamic Republic of); Vaezzadeh, Majid [Department of Physics, K.N.Toosi University of Technology, P.O. Box 15875-4416, Tehran (Iran, Islamic Republic of); Daneshmand, Gissoo [Department of Physics, K.N.Toosi University of Technology, P.O. Box 15875-4416, Tehran (Iran, Islamic Republic of); Kanzeghi, Ali [Department of Physics, K.N.Toosi University of Technology, P.O. Box 15875-4416, Tehran (Iran, Islamic Republic of)
2006-05-01
The magnetic behavior of Gd-based intermetallic compound (Gd{sub 2}Al{sub (1-x)}Au{sub x}) in the form of the powder and needle, is investigated. All the samples are an orthorhombic crystal structure. Only the compound with x=0.4 shows the Kondo effect (other compounds have a normal behavior). Although, for the compound in the form of powder, with x=0.4, the susceptibility measurement {chi}(T) shows two different stages. Moreover for (T>T{sub K2}) a fall of the value of {chi}(T) is observable, which indicates a weak presence of ferromagnetic phase. About the two stages of Kondo effect, we observe at the first (T{sub K1}) an increase of {chi}(T) and in the second stage (T{sub K2}) a new remarkable decrease of {chi}(T) (T{sub K1}>T{sub K2}). For the sample in the form of needles, the first stage is observable only under high magnetic field. This first stage could be corresponds to a narrow resonance between Kondo cloud and itinerant electron. The second stage, which is remarkably visible for the sample in the form of the powder, can be attribute to a complete polarization of Kondo cloud. Observation of these two Kondo stages could be due to the weak presence of RKKY contribution.
Two stages of Kondo effect and competition between RKKY and Kondo in Gd-based intermetallic compound
International Nuclear Information System (INIS)
Vaezzadeh, Mehdi; Yazdani, Ahmad; Vaezzadeh, Majid; Daneshmand, Gissoo; Kanzeghi, Ali
2006-01-01
The magnetic behavior of Gd-based intermetallic compound (Gd 2 Al (1-x) Au x ) in the form of the powder and needle, is investigated. All the samples are an orthorhombic crystal structure. Only the compound with x=0.4 shows the Kondo effect (other compounds have a normal behavior). Although, for the compound in the form of powder, with x=0.4, the susceptibility measurement χ(T) shows two different stages. Moreover for (T>T K2 ) a fall of the value of χ(T) is observable, which indicates a weak presence of ferromagnetic phase. About the two stages of Kondo effect, we observe at the first (T K1 ) an increase of χ(T) and in the second stage (T K2 ) a new remarkable decrease of χ(T) (T K1 >T K2 ). For the sample in the form of needles, the first stage is observable only under high magnetic field. This first stage could be corresponds to a narrow resonance between Kondo cloud and itinerant electron. The second stage, which is remarkably visible for the sample in the form of the powder, can be attribute to a complete polarization of Kondo cloud. Observation of these two Kondo stages could be due to the weak presence of RKKY contribution
Interaction effects in Aharonov-Bohm-Kondo rings
Komijani, Yashar; Yoshii, Ryosuke; Affleck, Ian
2013-12-01
We study the conductance through an Aharonov-Bohm ring, containing a quantum dot in the Kondo regime in one arm, at finite temperature and arbitrary electronic density. We develop a general method for this calculation based on changing the basis to the screening and nonscreening channels. We show that an unusual term appears in the conductance, involving the connected four-point Green's function of the conduction electrons. However, this term and the terms quadratic in the T matrix can be eliminated at sufficiently low temperatures, leading to an expression for the conductance linear in the Kondo T matrix. Explicit results are given for temperatures that are high compared to the Kondo temperature.
Spin dynamics and Kondo physics in optical tweezers
Lin, Yiheng; Lester, Brian J.; Brown, Mark O.; Kaufman, Adam M.; Long, Junling; Ball, Randall J.; Isaev, Leonid; Wall, Michael L.; Rey, Ana Maria; Regal, Cindy A.
2016-05-01
We propose to use optical tweezers as a toolset for direct observation of the interplay between quantum statistics, kinetic energy and interactions, and thus implement minimum instances of the Kondo lattice model in systems with few bosonic rubidium atoms. By taking advantage of strong local exchange interactions, our ability to tune the spin-dependent potential shifts between the two wells and complete control over spin and motional degrees of freedom, we design an adiabatic tunneling scheme that efficiently creates a spin-singlet state in one well starting from two initially separated atoms (one atom per tweezer) in opposite spin state. For three atoms in a double-well, two localized in the lowest vibrational mode of each tweezer and one atom in an excited delocalized state, we plan to use similar techniques and observe resonant transfer of two-atom singlet-triplet states between the wells in the regime when the exchange coupling exceeds the mobile atom hopping. Moreover, we argue that such three-atom double-tweezers could potentially be used for quantum computation by encoding logical qubits in collective spin and motional degrees of freedom. Current address: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
Quasiparticle scattering spectroscopy (QPS) of Kondo lattice heavy fermions
Greene, L. H.; Narasiwodeyar, S. M.; Banerjee, P.; Park, W. K.; Bauer, E. D.; Tobash, P. H.; Baumbach, R. E.; Ronning, F.; Sarrao, J. L.; Thompson, J. D.
2013-03-01
Point-contact spectroscopy (PCS) is a powerful technique to study electronic properties via measurements of non-linear current-voltage characteristic across a ballistic junction. It has been frequently adopted to investigate novel and/or unconventional superconductors by detecting the energy-dependent Andreev scattering. PCS of non-superconducting materials has been much rarely reported. From our recent studies on heavy fermions, we have frequently observed strongly bias-dependent and asymmetric conductance behaviors. Based on a Fano resonance model in a Kondo lattice, we attribute them to energy-dependent quasiparticle scattering off hybridized renormalized electronic states, dubbing it QPS. We will present our QPS results on several heavy-fermion systems and discuss QPS as a novel technique to probe the bulk spectroscopic properties of the electronic structure. For instance, it reveals that the hybridization gap in URu2Si2 opens well above the hidden order transition. The work at UIUC is supported by the U.S. DOE under Award No. DE-FG02-07ER46453 and the NSF DMR 12-06766, and the work at LANL is carried out under the auspices of the U.S. DOE, Office of Science.
Two-channel Hyperspectral LiDAR with a Supercontinuum Laser Source
Directory of Open Access Journals (Sweden)
Ruizhi Chen
2010-07-01
Full Text Available Recent advances in nonlinear fiber optics and compact pulsed lasers have resulted in creation of broadband directional light sources. These supercontinuum laser sources produce directional broadband light using cascaded nonlinear optical interactions in an optical fibre framework. This system is used to simultaneously measure distance and reflectance to demonstrate a technique capable of distinguishing between a vegetation target and inorganic material using the Normalized Difference Vegetation Index (NDVI parameters, while the range can be obtained from the waveform of the echoes. A two-channel, spectral range-finding system based on a supercontinuum laser source was used to determine its potential application of distinguishing the NDVI for Norway spruce, a coniferous tree, and its three-dimensional parameters at 600 nm and 800 nm. A prototype system was built using commercial components.
Two-point functions in a holographic Kondo model
Erdmenger, Johanna; Hoyos, Carlos; O'Bannon, Andy; Papadimitriou, Ioannis; Probst, Jonas; Wu, Jackson M. S.
2017-03-01
We develop the formalism of holographic renormalization to compute two-point functions in a holographic Kondo model. The model describes a (0 + 1)-dimensional impurity spin of a gauged SU( N ) interacting with a (1 + 1)-dimensional, large- N , strongly-coupled Conformal Field Theory (CFT). We describe the impurity using Abrikosov pseudo-fermions, and define an SU( N )-invariant scalar operator O built from a pseudo-fermion and a CFT fermion. At large N the Kondo interaction is of the form O^{\\dagger}O, which is marginally relevant, and generates a Renormalization Group (RG) flow at the impurity. A second-order mean-field phase transition occurs in which O condenses below a critical temperature, leading to the Kondo effect, including screening of the impurity. Via holography, the phase transition is dual to holographic superconductivity in (1 + 1)-dimensional Anti-de Sitter space. At all temperatures, spectral functions of O exhibit a Fano resonance, characteristic of a continuum of states interacting with an isolated resonance. In contrast to Fano resonances observed for example in quantum dots, our continuum and resonance arise from a (0 + 1)-dimensional UV fixed point and RG flow, respectively. In the low-temperature phase, the resonance comes from a pole in the Green's function of the form - i2, which is characteristic of a Kondo resonance.
Two-point functions in a holographic Kondo model
Energy Technology Data Exchange (ETDEWEB)
Erdmenger, Johanna [Institut für Theoretische Physik und Astrophysik, Julius-Maximilians-Universität Würzburg,Am Hubland, D-97074 Würzburg (Germany); Max-Planck-Institut für Physik (Werner-Heisenberg-Institut),Föhringer Ring 6, D-80805 Munich (Germany); Hoyos, Carlos [Department of Physics, Universidad de Oviedo, Avda. Calvo Sotelo 18, 33007, Oviedo (Spain); O’Bannon, Andy [STAG Research Centre, Physics and Astronomy, University of Southampton,Highfield, Southampton SO17 1BJ (United Kingdom); Papadimitriou, Ioannis [SISSA and INFN - Sezione di Trieste, Via Bonomea 265, I 34136 Trieste (Italy); Probst, Jonas [Rudolf Peierls Centre for Theoretical Physics, University of Oxford,1 Keble Road, Oxford OX1 3NP (United Kingdom); Wu, Jackson M.S. [Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487 (United States)
2017-03-07
We develop the formalism of holographic renormalization to compute two-point functions in a holographic Kondo model. The model describes a (0+1)-dimensional impurity spin of a gauged SU(N) interacting with a (1+1)-dimensional, large-N, strongly-coupled Conformal Field Theory (CFT). We describe the impurity using Abrikosov pseudo-fermions, and define an SU(N)-invariant scalar operator O built from a pseudo-fermion and a CFT fermion. At large N the Kondo interaction is of the form O{sup †}O, which is marginally relevant, and generates a Renormalization Group (RG) flow at the impurity. A second-order mean-field phase transition occurs in which O condenses below a critical temperature, leading to the Kondo effect, including screening of the impurity. Via holography, the phase transition is dual to holographic superconductivity in (1+1)-dimensional Anti-de Sitter space. At all temperatures, spectral functions of O exhibit a Fano resonance, characteristic of a continuum of states interacting with an isolated resonance. In contrast to Fano resonances observed for example in quantum dots, our continuum and resonance arise from a (0+1)-dimensional UV fixed point and RG flow, respectively. In the low-temperature phase, the resonance comes from a pole in the Green’s function of the form −i〈O〉{sup 2}, which is characteristic of a Kondo resonance.
International Nuclear Information System (INIS)
Nguyen Bich Ha; Nguyen Van Hop
2009-01-01
The Kondo and Fano resonances in the two-point Green's function of the single-level quantum dot were found and investigated in many previous works by means of different numerical calculation methods. In this work we present the derivation of the analytical expressions of resonance terms in the expression of the two-point Green's function. For that purpose the system of Dyson equations for the two-point nonequilibrium Green's functions in the complex-time Keldysh formalism was established in the second order with respect to the tunneling coupling constants and the mean field approximation. This system of Dyson equations was solved exactly and the analytical expressions of the resonance terms are derived. The conditions for the existence of Kondo or Fano resonances are found.
International Nuclear Information System (INIS)
Schlottmann, P.
1998-01-01
Properties of highly correlated electrons, such as heavy fermion compounds, metal-insulator transitions, one-dimensional conductors and systems of restricted dimensionality are studied theoretically. The main focus is on Kondo insulators and impurity bands due to Kondo holes, the low-temperature magnetoresistivity of heavy fermion alloys, the n-channel Kondo problem, mesoscopic systems and one-dimensional conductors
Anomalous Kondo-Switching Effect of a Spin-Flip Quantum Dot Embedded in an Aharonov-Bohm Ring
International Nuclear Information System (INIS)
Chen Xiongwen; Shi Zhengang; Song Kehui
2009-01-01
We theoretically investigate the Kondo effect of a quantum dot embedded in a mesoscopic Aharonov-Bohm (AB) ring in the presence of the spin flip processes by means of the one-impurity Anderson Hamiltonian. Based on the slave-boson mean-field theory, we find that in this system the persistent current (PC) sensitively depends on the parity and size of the AB ring and can be tuned by the spin-flip scattering (R). In the small AB ring, the PC is suppressed due to the enhancing R weakening the Kondo resonance. On the contrary, in the large AB ring, with R increasing, the peak of PC firstly moves up to max-peak and then down. Especially, the PC phase shift of π appears suddenly with the proper value of R, implying the existence of the anomalous Kondo effect in this system. Thus this system may be a candidate for quantum switch. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Transient dynamics of a quantum-dot: From Kondo regime to mixed valence and to empty orbital regimes
Cheng, YongXi; Li, ZhenHua; Wei, JianHua; Nie, YiHang; Yan, YiJing
2018-04-01
Based on the hierarchical equations of motion approach, we study the time-dependent transport properties of a strongly correlated quantum dot system in the Kondo regime (KR), mixed valence regime (MVR), and empty orbital regime (EOR). We find that the transient current in KR shows the strongest nonlinear response and the most distinct oscillation behaviors. Both behaviors become weaker in MVR and diminish in EOR. To understand the physical insight, we examine also the corresponding dot occupancies and the spectral functions, with their dependence on the Coulomb interaction, temperature, and applied step bias voltage. The above nonlinear and oscillation behaviors could be understood as the interplay between dynamical Kondo resonance and single electron resonant-tunneling.
Direct observation of the orbital spin Kondo effect in gallium arsenide quantum dots
Shang, Ru-Nan; Zhang, Ting; Cao, Gang; Li, Hai-Ou; Xiao, Ming; Guo, Guang-Can; Guo, Guo-Ping
2018-02-01
Besides the spin Kondo effect, other degrees of freedom can give rise to the pseudospin Kondo effect. We report a direct observation of the orbital spin Kondo effect in a series-coupled gallium arsenide (GaAs) double quantum dot device where orbital degrees act as pseudospin. Electron occupation in both dots induces a pseudospin Kondo effect. In a region of one net spin impurity, complete spectra with three resonance peaks are observed. Furthermore, we observe a pseudo-Zeeman effect and demonstrate its electrical controllability for the artificial pseudospin in this orbital spin Kondo process via gate voltage control. The fourfold degeneracy point is realized at a specific value supplemented by spin degeneracy, indicating a transition from the SU(2) to the SU(4) Kondo effect.
Two-channel totally asymmetric simple exclusion processes
International Nuclear Information System (INIS)
Pronina, Ekaterina; Kolomeisky, Anatoly B
2004-01-01
Totally asymmetric simple exclusion processes, consisting of two coupled parallel lattice chains with particles interacting with hard-core exclusion and moving along the channels and between them, are considered. In the limit of strong coupling between the channels, the particle currents, density profiles and a phase diagram are calculated exactly by mapping the system into an effective one-channel totally asymmetric exclusion model. For intermediate couplings, a simple approximate theory, that describes the particle dynamics in vertical clusters of two corresponding parallel sites exactly and neglects the correlations between different vertical clusters, is developed. It is found that, similarly to the case of one-channel totally asymmetric simple exclusion processes, there are three stationary state phases, although the phase boundaries and stationary properties strongly depend on inter-channel coupling. Extensive computer Monte Carlo simulations fully support the theoretical predictions
Interplay between surface and bulk states in the Topological Kondo Insulator SmB6
Biswas, Sangram; Hatnean, Monica Ciomaga; Balakrishnan, Geetha; Bid, Aveek
Kondo insulator SmB6 is predicted to have topologically protected conducting surface states(TSS). We have studied electrical transport through surface states(SS) at ultra-low temperatures in single crystals of SmB6 using local-nonlocal transport scheme and found a large nonlocal signal at temperatures lower than bulk Kondo gap scale. Using resistance fluctuation spectroscopy, we probed the local and nonlocal transport channels and showed that at low temperatures, transport in this system takes place only through SS. The measured noise in this temperature range arises due to Universal Conductance Fluctuations whose statistics was found to be consistent with theoretical predictions for that of 2D systems in the Symplectic symmetry class. We studied the temperature dependence of noise and found that, unlike the topological insulators of the dichalcogenide family, the noise in surface and bulk conduction channels in SmB6 are uncorrelated - at sufficiently low temperatures, the bulk has no discernible contribution to electrical transport in SmB6 making it an ideal platform for probing the physics of TSS. Nanomission, Department of Science & Technology (DST) and Indian Institute of Scienc and EPSRC, UK, Grant EP/L014963/1.
Kondo Effect of U Impurities in Dilute (YU)2Zn17
Takagi, Shigeru; Suzuki, Hiroyuki; Anzai, Kousuke
2001-10-01
Extending previous work on single-site properties of U ions in (LaU)2Zn17, we have investigated, from ρ(T), χ(T) and Cp(T) on single crystals, (Y1-xUx)2Zn17 with x=0.025 and 0.050, which has almost the same unit-cell volume as an antiferromagnetic heavy-electron compound U2Zn17. Remarkable features in the dilute-impurity limit have been clarified, which include Kondo behavior of ρ(T), large and almost isotropic χimp(T), and strongly enhanced Cimp(T)/T with gigantic γimp=2.02 2.05 J/K2·mole-U as T→0 due to a low characteristic energy-scale of the system. It is shown that gross features of the data are explained in terms of the conventional Kondo effect in the presence of the crystal field with the U3+ \\varGamma6 doublet ground state. It is also shown that the variation of γ with the unit-cell volume in related systems is not explained as a volume effect on TK and that even the behavior of fictitious “paramagnetic” U2Zn17 is not described as a collection of U impurities in dilute (YU)2Zn17.
Two-channel interaction models in cavity QED
International Nuclear Information System (INIS)
Wang, L.
1993-01-01
The authors introduce four fully quantized models of light-matter interactions in optical or microwave cavities. These are the first exactly soluble models in cavity quantum electrodynamics (cavity QED) that provide two transition channels for the flipping of atomic states. In these models a loss-free cavity is assumed to support three or four quantized field modes, which are coupled to a single atom. The atom exchanges photons with the cavity, in either the Raman configuration including both Stokes and anti-Stokes modes, or through two-photon cascade processes. The authors obtain the effective Hamiltonians for these models by adiabatically eliminating an off-resonant intermediate atomic level, and discuss their novel properties in comparison to the existing one-channel Jaynes-Cummings models. They give a detailed description of a method to find exact analytic solutions for the eigenfunctions and eigenvalues for the Hamiltonians of four models. These are also valid when the AC Stark shifts are included. It is shown that the eigenvalues can be expressed in very simple terms, and formulas for normalized eigenvectors are also given, as well as discussions of some of their simple properties. Heisenberg picture equations of motions are derived for several operators with solutions provided in a couple of cases. The dynamics of the systems with both Fock state and coherent state fields are demonstrated and discussed using the model's two key variables, the atomic inversion and the expectation value of photon number. Clear evidences of high efficiency mode-mixing are seen in both the Raman and cascade configurations, and different kinds of collapses and revivals are encountered in the atomic inversions. Effects of several factors like the AC Stark shift and variations in the complex coupling constants are also illustrated
Quantum critical scaling and fluctuations in Kondo lattice materials
Yang, Yi-feng; Pines, David; Lonzarich, Gilbert
2017-01-01
We propose a phenomenological framework for three classes of Kondo lattice materials that incorporates the interplay between the fluctuations associated with the antiferromagnetic quantum critical point and those produced by the hybridization quantum critical point that marks the end of local moment behavior. We show that these fluctuations give rise to two distinct regions of quantum critical scaling: Hybridization fluctuations are responsible for the logarithmic scaling in the density of states of the heavy electron Kondo liquid that emerges below the coherence temperature T∗, whereas the unconventional power law scaling in the resistivity that emerges at lower temperatures below TQC may reflect the combined effects of hybridization and antiferromagnetic quantum critical fluctuations. Our framework is supported by experimental measurements on CeCoIn5, CeRhIn5, and other heavy electron materials. PMID:28559308
Inelastic tunneling spectroscopy for magnetic atoms and the Kondo resonance
International Nuclear Information System (INIS)
Goldberg, E C; Flores, F
2013-01-01
The interaction between a single magnetic atom and the metal environment (including a magnetic field) is analyzed by introducing an ionic Hamiltonian combined with an effective crystal-field term, and by using a Green-function equation of motion method. This approach describes the inelastic electron tunneling spectroscopy and the Kondo resonances as due to atomic spin fluctuations associated with electron co-tunneling processes between the leads and the atom. We analyze in the case of Fe on CuN the possible spin fluctuations between states with S = 2 and 3/2 or 5/2 and conclude that the experimentally found asymmetries in the conductance with respect to the applied bias, and its marked structures, are well explained by the 2↔3/2 spin fluctuations. The case of Co is also considered and shown to present, in contrast with Fe, a resonance at the Fermi energy corresponding to a Kondo temperature of 6 K. (paper)
Field induced magnetic quantum critical behavior in the Kondo necklace model
International Nuclear Information System (INIS)
Reyes, Daniel; Continentino, Mucio
2008-01-01
The Kondo necklace model augmented by a Zeeman term, serves as a useful model for heavy fermion compounds in an applied magnetic field. The phase diagram and thermodynamic behavior for arbitrary dimensions d has been investigated previously in the zero field case [D. Reyes, M. Continentino, Phys. Rev. B 76 (2007) 075114. ]. Here we extend the treatment to finite fields using a generalized bond operator representation for the localized and conduction electrons spins. A decoupling scheme on the double time Green's functions yields the dispersion relation for the excitations of the system. Two critical magnetic fields are found namely, a critical magnetic field called henceforth h c1 and a saturation field nominated h c2 . Then three important regions can be investigated: (i) Kondo spin liquid state (KSL) at low fields h c1 ; (ii) destruction of KSL state at h≥h c1 and appearance of a antiferromagnetic state; and (iii) saturated paramagnetic region above the upper critical field h c2
Towards quantum simulation of the Kondo-Lattice-Model
Energy Technology Data Exchange (ETDEWEB)
Kochanke, Andre
2017-04-25
Ultracold quantum gases of alkaline-earth-like metals are a versatile tool to investigate interacting many-body physics by realizing clean and controllable experimental model systems. Their intriguing properties range from energetically low-lying clock transitions, which allow for high-resolution spectroscopy, over meta-stable states, which can be regarded as a second species with orbital degree of freedom, to SU(N) symmetry, allowing novel magnetic phases. These open up new possibilities for quantum simulators. Using them in combination with optical lattices dissipative Fermi-Hubbard models and the Kondo-lattice-model can be realized, two promising examples for probing strongly correlated systems. This thesis presents an experimental apparatus for producing ultracold samples of fermionic {sup 173}Yb (N≤6). A new bicolor dipole trap was implemented with a final, average trap frequency of anti ω=36 Hz. Using optical, resonant pumping and an Optical-Stern-Gerlach scheme, the spin mixture can arbitrarily be changed from a six- to a one-component gas. Typically the degenerate Fermi gases consist of 87000 atoms at 17.5% T{sub F} (N=6) and of 47000 atoms at 19.4% T{sub F} (N=1). The lowest lying meta-stable state {sup 3}P{sub 0} (578 nm) is coherently controlled using a clock-laser setup with a linewidth of FWHM=1 Hz by means of Rabi oscillations or rapid adiabatic passage. By conducting spectroscopic measurements in a 3D magic lattice (759 nm) we demonstrate inter band transitions and observe the {sup 1}S{sub 0}<=>{sup 3}P{sub 0} excitation with a resolution of FWHM=50(2) Hz. Applying these techniques to a two-component spin mixture reveals a shift of the clock-transition caused by spin-exchange interaction between the orbital symmetric vertical stroke eg right angle {sup +} vertical stroke ↑↓ right angle {sup -} and the orbital antisymmetric vertical stroke eg right angle {sup -} vertical stroke ↑↓ right angle {sup +} state. Using the inelastic properties of
Spins of adsorbed molecules investigated by the detection of Kondo resonance
Komeda, Tadahiro
2014-12-01
Surface magnetism has been one of the platforms to explore the magnetism in low dimensions. It is also a key component for the development of quantum information processes, which utilizes the spin degree of freedom. The Kondo resonance is a phenomenon that is caused by an interaction between an isolated spin and conduction electrons. First observed in the 1930s as an anomalous increase in the low-temperature resistance of metals embedded with magnetic atoms, the Kondo physics mainly studied the effects of bulk magnetic impurities in the resistivity. In the last 15 years it has undergone a revival by a scanning tunneling microscope (STM) which enables the measurement of the Kondo resonance at surfaces using an atomic scale point contact. The detection of the Kondo resonance can be a powerful tool to explore surface magnetism. In this article, I review recent studies of the surface spin of adsorbed molecules by the detection of the Kondo resonance. Researches on metal phthalocyanine (MPc) and porphyrin molecules will be examined. In addition, the Kondo resonance for double-decker lanthanoide Pc molecules will be discussed. Some of the double-decker Pc molecules show single-molecule magnet (SMM) behavior, which attracts attention as a material for electronic devices. For both classes, the ligand plays a crucial role in determining the parameters of the Kondo resonance, such as the Kondo temperature and the change of the shape from peak to Fano-dip. In addition, the spin in delocalized molecular orbital forms the Kondo resonance, which shows significant differences from the Kondo resonance formed by the metal spins. Since molecular orbital can be tuned in a flexible manner by the design of the molecule, the Kondo resonance formed by delocalized molecular orbital might expand the knowledge of this field.
Lifetime predictions for dimmable two-channel drivers for color tuning luminaires
Energy Technology Data Exchange (ETDEWEB)
Davis, Lynn [RTI International, Research Triangle Park, NC (United States); Smith, Aaron [Finelite Inc., Union City, CA (United States); Clark, Terry [Finelite Inc., Union City, CA (United States); Mills, Karmann [RTI International, Research Triangle Park, NC (United States); Perkins, Curtis [RTI International, Research Triangle Park, NC (United States)
2017-05-30
Two-channel tunable white lighting (TWL) systems represent the next wave of solid-state lighting (SSL) systems and promise flexibility in light environment while maintaining the high reliability and luminous efficacy expected with SSL devices. TWL systems utilize LED assemblies consisting of two different LED spectra (i.e., often a warm white assembly and a cool white assembly) that are integrated into modules. While these systems provide the ability to adjust the lighting spectrum to match the physiology needs of the task at hand, they also are a potentially more complex lighting system from a performance and reliability perspective. We report an initial study on the reliability performance of such lighting systems including an examination of the lumen maintenance and chromaticity stability of warm white and cool white LED assemblies and the multi-channel driver that provides power to the assemblies. Accelerated stress tests including operational bake tests conducted at 75°C and 95°C were used to age the LED modules, while more aggressive temperature and humidity tests were used for the drivers in this study. Small differences in the performance between the two LED assemblies were found and can be attributed to the different phosphor chemistries. The lumen maintenances of both LED assemblies were excellent. The warm white LED assemblies were found to shift slightly in the green color direction over time while the cool white LED assemblies shifted slightly in the yellow color direction. The net result of these chromaticity shifts is a small, barely perceptible reduction in the tuning range after 6,000 hours of exposure to an accelerating elevated temperature of 75°C.
Spin dynamics of the Kondo insulator CeNiSn approaching the metallic phase
DEFF Research Database (Denmark)
Schröder, A.; Aeppli, G.; Mason, T.E.
1997-01-01
The spin dynamics of Kondo insulators has been studied by high-resolution magnetic neutron spectroscopy at a triple-axes spectrometer on CeNi1-xCuxSn single crystals using a vertical 9 T magnet. While upon doping (x = 0.13) the spin gap of the Kondo insulator CeNiSn collapses at the transition to...
International Nuclear Information System (INIS)
Oliveira, A.C.J.G. de; Andrade Lima, F.R. de
1989-01-01
The present work is an application of the perturbation theory (Matricial formalism) to a simplified two channels model, for sensitivity calculations in PWR cores. Expressions for some sensitivity coefficients of thermohydraulic interest were developed from the proposed model. The code CASNUR.FOR was written in FORTRAN to evaluate these sensitivity coefficients. The comparison between results obtained from the matrical formalism of pertubation theory with those obtained directly from the two channels model, makes evident the efficiency and potentiality of this perturbation method for nuclear reactor cores sensitivity calculations. (author) [pt
The 1D Kondo lattice model at criticality
International Nuclear Information System (INIS)
Gulacsi, M.
1998-01-01
The transition from a ferromagnetic phase, to a disordered paramagnetic phase, which occurs in one-dimensional Kondo lattice models is described. The transition is the quantum order-disorder transition of the transverse-field Ising chain type, and reflects ferromagnetically ordered regions of localized spins being gradually destroyed as the coupling to the conduction electrons is reduced. For incommensurate conduction band fillings, the low-energy properties of the localized spins near the transition are dominated by anomalous ordered (disordered) regions of localized spins which survive into the ferromagnetic (paramagnetic) phase. (Copyright (1998) World Scientific Publishing Co. Pte. Ltd)
Fermionology in the Kondo-Heisenberg model: the case of CeCoIn5
Zhong, Yin; Zhang, Lan; Lu, Han-Tao; Luo, Hong-Gang
2015-09-01
The Fermi surface of heavy electron systems plays a fundamental role in understanding their variety of puzzling phenomena, for example, quantum criticality, strange metal behavior, unconventional superconductivity and even enigmatic phases with yet unknown order parameters. The spectroscopy measurement of the typical heavy fermion superconductor CeCoIn5 has demonstrated multi-Fermi surface structure, which has not been studied in detail theoretically in a model system like the Kondo-Heisenberg model. In this work, we take a step toward such a theoretical model by revisiting the Kondo-Heisenberg model. It is found that the usual self-consistent calculation cannot reproduce the fermionology of the experimental observation of the system due to the sign binding between the hopping of the conduction electrons and the mean-field valence-bond order. To overcome such inconsistency, the mean-field valence-bond order is considered as a free/fitting parameter to correlate them with real-life experiments as performed in recent experiments [M.P. Allan, F. Massee, D.K. Morr, J. Van Dyke, A.W. Rost, A.P. Mackenzie, C. Petrovic, J.C. Davis, Nat. Phys. 9, 468 (2013); J. Van Dyke, F. Massee, M.P. Allan, J.C. Davis, C. Petrovic, D.K. Morr, Proc. Natl. Acad. Sci. 111, 11663 (2014)], which also explicitly reflects the intrinsic dispersion of local electrons observed in experimental measurements. Given the fermionology, the calculated effective mass enhancement, entropy, superfluid density and Knight shift are all in qualitative agreement with the experimental results of CeCoIn5, which confirms our assumption. Our result supports a d_{x^2 - y^2 }-wave pairing structure in the heavy fermion material CeCoIn5.
Formation of spin-polarons in the ferromagnetic Kondo lattice model away from half-filling
International Nuclear Information System (INIS)
Arredondo, Y; Navarro, O; Vallejo, E; Avignon, M
2012-01-01
Even though realistic one-dimensional experiments in the field of half-metallic semiconductors are not at hand yet, we are interested in the underlying fundamental physics. In this regard we study a one-dimensional ferromagnetic Kondo lattice model, a model in which a conduction band is coupled ferromagnetically to a background of localized d moments with coupling constant J H , and investigate the T = 0 phase diagram as a function of the antiferromagnetic interaction J between the localized moments and the band-filling n, since it has been observed that doping of the compounds has led to formation of magnetic domains. We explore the spin-polaron formation by looking at the nearest-neighbour correlation functions in the spin and charge regimes for which we use the density matrix renormalization group method, which is a highly efficient method to investigate quasi-one-dimensional strongly correlated systems. (paper)
International Nuclear Information System (INIS)
Johnson, M.; Matulik, M.
1994-01-01
The digital oscilloscope allows one to make numerous timing measurements, but just how good are those measurements? This document describes a procedure which can be used to determine the accuracy and precision to which a digital oscilloscope can make various two channel timing measurements
Two-channel recoder for magnetometer with energy-independent mass memory device
International Nuclear Information System (INIS)
Korzinin, V.N.; Selivanov, A.M.
1993-01-01
The paper describes a two-channel digit-to-analog recorder designed for converting the sequence of pulses from proton magnetometer (MMH-203) outlet; the device enables processing of the pulses and their recording in RAM and on the tape of the analog recorder. The availability of nonvolotile RAM allows to transmit digit information to a computer (BK-0010) for its further processing
Single- or multi-flavor Kondo effect in graphene
Zhu, Zhen-Gang; Ding, Kai-He; Berakdar, Jamal
2010-06-01
Based on the tight-binding formalism, we investigate the Anderson and the Kondo model for an adatom magnetic impurity above graphene. Different impurity positions are analyzed. Employing a partial-wave representation we study the nature of the coupling between the impurity and the conducting electrons. The components from the two Dirac points are mixed while interacting with the impurity. Two configurations are considered explicitly: the adatom is above one atom (ADA), the other case is the adatom above the center the honeycomb (ADC). For ADA the impurity is coupled with one flavor for both A and B sublattice and both Dirac points. For ADC the impurity couples with multi-flavor states for a spinor state of the impurity. We show, explicitly for a 3d magnetic atom, dz2, (dxz,dyz), and (dx2- y2,dxy) couple respectively with the Γ1, Γ5(E1), and Γ6(E2) representations (reps) of C6v group in ADC case. The bases for these reps of graphene are also derived explicitly. For ADA we calculate the Kondo temperature.
Interaction effect in the Kondo energy of the periodic Anderson-Hubbard model
Itai, K.; Fazekas, P.
1996-07-01
We extend the periodic Anderson model by switching on a Hubbard U for the conduction band. The nearly integral valent limit of the Anderson-Hubbard model is studied with the Gutzwiller variational method. The lattice Kondo energy shows U dependence both in the prefactor and the exponent. Switching on U reduces the Kondo scale, which can be understood to result from the blocking of hybridization. At half filling, we find a Brinkman-Rice-type transition from a Kondo insulator to a Mott insulator. Our findings should be relevant for a number of correlated two-band models of recent interest.
Kondo dynamics of quasiparticle tunneling in a two-reservoir Anderson model.
Hong, Jongbae
2011-07-13
We study the Kondo dynamics in a two-reservoir Anderson impurity model in which quasiparticle tunneling occurs between two reservoirs. We show that singlet hopping is an essential component of Kondo dynamics in the quasiparticle tunneling. We prove that two resonant tunneling levels exist in the two-reservoir Anderson impurity model and the quasiparticle tunnels through one of these levels when a bias is applied. The Kondo dynamics is explained by obtaining the retarded Green's function. We obtain the analytic expressions of the spectral weights of coherent peaks by analyzing the Green's function at the atomic limit.
Kondo dynamics of quasiparticle tunneling in a two-reservoir Anderson model
International Nuclear Information System (INIS)
Hong, Jongbae
2011-01-01
We study the Kondo dynamics in a two-reservoir Anderson impurity model in which quasiparticle tunneling occurs between two reservoirs. We show that singlet hopping is an essential component of Kondo dynamics in the quasiparticle tunneling. We prove that two resonant tunneling levels exist in the two-reservoir Anderson impurity model and the quasiparticle tunnels through one of these levels when a bias is applied. The Kondo dynamics is explained by obtaining the retarded Green's function. We obtain the analytic expressions of the spectral weights of coherent peaks by analyzing the Green's function at the atomic limit.
Kang, Chang-Jong; Choi, Hong Chul; Kim, Kyoo; Min, B I
2015-04-24
We have investigated temperature-dependent behaviors of electronic structure and resistivity in a mixed-valent golden phase of SmS, based on the dynamical mean-field-theory band-structure calculations. Upon cooling, the coherent Sm 4f bands are formed to produce the hybridization-induced pseudogap near the Fermi level, and accordingly the topology of the Fermi surface is changed to exhibit a Lifshitz-like transition. The surface states emerging in the bulk gap region are found to be not topologically protected states but just typical Rashba spin-polarized states, indicating that SmS is not a topological Kondo semimetal. From the analysis of anomalous resistivity behavior in SmS, we have identified universal energy scales, which characterize the Kondo-mixed-valent semimetallic systems.
Two-Channel SPR Sensor Combined Application of Polymer- and Vitreous-Clad Optic Fibers.
Wei, Yong; Su, Yudong; Liu, Chunlan; Nie, Xiangfei; Liu, Zhihai; Zhang, Yu; Zhang, Yonghui
2017-12-09
By combining a polymer-clad optic fiber and a vitreous-clad optic fiber, we proposed and fabricated a novel optic fiber surface plasmon resonance (SPR) sensor to conduct two-channel sensing at the same detection area. The traditional optic fiber SPR sensor has many disadvantages; for example, removing the cladding requires corrosion, operating it is dangerous, adjusting the dynamic response range is hard, and producing different resonance wavelengths in the sensing area to realize a multi-channel measurement is difficult. Therefore, in this paper, we skillfully used bare fiber grinding technology and reverse symmetry welding technology to remove the cladding in a multi-mode fiber and expose the evanescent field. On the basis of investigating the effect of the grinding angle on the dynamic range change of the SPR resonance valley wavelength and sensitivity, we combined polymer-clad fiber and vitreous-clad fiber by a smart design structure to realize at a single point a two-channel measurement fiber SPR sensor. In this paper, we obtained a beautiful spectral curve from a multi-mode fiber two-channel SPR sensor. In the detection range of the refractive rate between 1.333 RIU and 1.385 RIU, the resonance valley wavelength of channel Ⅰ shifted from 622 nm to 724 nm with a mean average sensitivity of 1961 nm/RIU and the resonance valley wavelength of channel Ⅱ shifted from 741 nm to 976 nm with a mean average sensitivity of 4519 nm/RIU.
Electrostatic tuning of Kondo effect in a rare-earth-doped wide-band-gap oxide
Li, Yongfeng; Deng, Rui; Lin, Weinan; Tian, Yufeng; Peng, Haiyang; Yi, Jiabao; Yao, Bin; Wu, Tao
2013-01-01
As a long-lived theme in solid-state physics, the Kondo effect reflects the many-body physics involving the short-range Coulomb interactions between itinerant electrons and localized spins in metallic materials. Here we show that the Kondo effect is present in ZnO, a prototypical wide-band-gap oxide, doped with a rare-earth element (Gd). The localized 4f electrons of Gd ions do not produce remanent magnetism, but interact strongly with the host electrons, giving rise to a saturating resistance upturn and negative magnetoresistance at low temperatures. Furthermore, the Kondo temperature and resistance can be electrostatically modulated using electric-double-layer gating with liquid ionic electrolyte. Our experiments provide the experimental evidence of tunable Kondo effect in ZnO, underscoring the magnetic interactions between localized and itinerant electrons and the emergent transport behaviors in such doped wide-band-gap oxides.
Intra- and inter-shell Kondo effects in carbon nanotube quantum dots
Krychowski, Damian; Lipiński, Stanisław
2018-01-01
The linear response transport properties of carbon nanotube quantum dot in the strongly correlated regime are discussed. The finite-U mean field slave boson approach is used to study many-body effects. Magnetic field can rebuilt Kondo correlations, which are destroyed by the effect of spin-orbit interaction or valley mixing. Apart from the field induced revivals of SU(2) Kondo effects of different types: spin, valley or spin-valley, also more exotic phenomena appear, such as SU(3) Kondo effect. Threefold degeneracy occurs due to the effective intervalley exchange induced by short-range part of Coulomb interaction or due to the intershell mixing. In narrow gap nanotubes the full spin-orbital degeneracy might be recovered in the absence of magnetic field opening the condition for a formation of SU(4) Kondo resonance.
Electrostatic tuning of Kondo effect in a rare-earth-doped wide-band-gap oxide
Li, Yongfeng
2013-04-29
As a long-lived theme in solid-state physics, the Kondo effect reflects the many-body physics involving the short-range Coulomb interactions between itinerant electrons and localized spins in metallic materials. Here we show that the Kondo effect is present in ZnO, a prototypical wide-band-gap oxide, doped with a rare-earth element (Gd). The localized 4f electrons of Gd ions do not produce remanent magnetism, but interact strongly with the host electrons, giving rise to a saturating resistance upturn and negative magnetoresistance at low temperatures. Furthermore, the Kondo temperature and resistance can be electrostatically modulated using electric-double-layer gating with liquid ionic electrolyte. Our experiments provide the experimental evidence of tunable Kondo effect in ZnO, underscoring the magnetic interactions between localized and itinerant electrons and the emergent transport behaviors in such doped wide-band-gap oxides.
Non-equilibrium scaling analysis of the Kondo model with voltage bias
International Nuclear Information System (INIS)
Fritsch, Peter; Kehrein, Stefan
2009-01-01
The quintessential description of Kondo physics in equilibrium is obtained within a scaling picture that shows the buildup of Kondo screening at low temperature. For the non-equilibrium Kondo model with a voltage bias, the key new feature are decoherence effects due to the current across the impurity. In the present paper, we show how one can develop a consistent framework for studying the non-equilibrium Kondo model within a scaling picture of infinitesimal unitary transformations (flow equations). Decoherence effects appear naturally in third order of the β-function and dominate the Hamiltonian flow for sufficiently large voltage bias. We work out the spin dynamics in non-equilibrium and compare it with finite temperature equilibrium results. In particular, we report on the behavior of the static spin susceptibility including leading logarithmic corrections and compare it with the celebrated equilibrium result as a function of temperature.
Competition between direct interaction and Kondo effect: Renormalization-group approach
International Nuclear Information System (INIS)
Allub, R.
1988-03-01
Via the Wilson renormalization-group approach, the effect of the competition between direct interaction (J L ) and Kondo coupling is studied, in the magnetic susceptibility of a model with two different magnetic impurities. For the ferromagnetic interaction (J L > 0) between the localized impurities, we find a magnetic ground state and a divergent susceptibility at low temperatures. For (J L < 0), two different Kondo temperatures and a non-magnetic ground state are distinguished. (author). 12 refs, 1 fig
Model for a Ferromagnetic Quantum Critical Point in a 1D Kondo Lattice
Komijani, Yashar; Coleman, Piers
2018-04-01
Motivated by recent experiments, we study a quasi-one-dimensional model of a Kondo lattice with ferromagnetic coupling between the spins. Using bosonization and dynamical large-N techniques, we establish the presence of a Fermi liquid and a magnetic phase separated by a local quantum critical point, governed by the Kondo breakdown picture. Thermodynamic properties are studied and a gapless charged mode at the quantum critical point is highlighted.
Quenching of overcompensated Kondo impurities via channel asymmetry
International Nuclear Information System (INIS)
Schlottmann, P.; Lee, K.
1996-01-01
We consider a spin-1/2 impurity interacting with conduction electrons in two different orbital channels via an isotropic spin exchange. The exchange is the same for both channels, but a crystalline field breaks the symmetry between the orbital channels. This corresponds to a splitting of the conduction electron Γ 8 into two doublets in the quadrupolar Kondo effect and to the application of an external magnetic field in the electron assisted tunneling of an atom in a double-well potential. We study the ground-state properties of the impurity as a function of the magnetic and crystalline fields. The crystalline field quenches the critical behavior of the overcompensated fixed point: The impurity ground state is a singlet. (orig.)
Green's function approach to the anisotropic Kondo-necklace lattice
International Nuclear Information System (INIS)
Rezania, H.; Langari, A.; Thalmeier, P.
2007-01-01
Full text: We have studied the effect of anisotropy on the quantum phase transition of the 2D anisotropic Kondo necklace lattice [1] within a Green's function approach [2]. In the disordered phase the ground state is the product of all singlet bonds between itinerant and localized spins. It is separated by a finite energy gap from the triplet excited states. The quantum phase transition to the antiferromagnetically ordered phase takes place where the gap vanishes. In this approach we use the bond operator formalism introduced in Ref.[3] where each bond is represented by the singlet and triplet operators. The Kondo necklace Hamiltonian in the bond operator representation is composed of the kinetic energy and pairing part (H2), the two particle interaction (H4) of the boson gas and a term which includes three boson operators (H3). In order to ensure that the physical states are either singlets or triplets we impose the hard-core condition by introducing an infinite on-site repulsion between triplet bosons (H U ). The scattering vertex in the ladder approximation satisfies the Bethe-Salpeter equation [4]. By calculating the scattering vertex function we obtain the self energy contribution of the Hamiltonian H U . We have added the second order contribution of the self energy of H3 to the self energy of H U . It should be noted that the non conservation of triplet boson numbers requires the inclusion of the anomalous Green's functions. We treat H 4 in mean-field theory, by splitting the quartic operator into all possible pairs. Finally we obtain the renormalization of coefficients in the H 2 Hamiltonian and calculate the energy gap. Indeed at the critical point a condensation of triplet bosons occurs. We have numerically found the critical point of this model and compared our results with the corresponding mean field values [5]. Moreover, the critical exponent of the energy gap can be obtained more accurately than the mean field results. (authors)
Roosen, David; Wegewijs, Maarten R.; Hofstetter, Walter
2008-02-01
We investigate the time-dependent Kondo effect in a single-molecule magnet (SMM) strongly coupled to metallic electrodes. Describing the SMM by a Kondo model with large spin S>1/2, we analyze the underscreening of the local moment and the effect of anisotropy terms on the relaxation dynamics of the magnetization. Underscreening by single-channel Kondo processes leads to a logarithmically slow relaxation, while finite uniaxial anisotropy causes a saturation of the SMM’s magnetization. Additional transverse anisotropy terms induce quantum spin tunneling and a pseudospin-1/2 Kondo effect sensitive to the spin parity.
Two-Channel SPR Sensor Combined Application of Polymer- and Vitreous-Clad Optic Fibers
Directory of Open Access Journals (Sweden)
Yong Wei
2017-12-01
Full Text Available By combining a polymer-clad optic fiber and a vitreous-clad optic fiber, we proposed and fabricated a novel optic fiber surface plasmon resonance (SPR sensor to conduct two-channel sensing at the same detection area. The traditional optic fiber SPR sensor has many disadvantages; for example, removing the cladding requires corrosion, operating it is dangerous, adjusting the dynamic response range is hard, and producing different resonance wavelengths in the sensing area to realize a multi-channel measurement is difficult. Therefore, in this paper, we skillfully used bare fiber grinding technology and reverse symmetry welding technology to remove the cladding in a multi-mode fiber and expose the evanescent field. On the basis of investigating the effect of the grinding angle on the dynamic range change of the SPR resonance valley wavelength and sensitivity, we combined polymer-clad fiber and vitreous-clad fiber by a smart design structure to realize at a single point a two-channel measurement fiber SPR sensor. In this paper, we obtained a beautiful spectral curve from a multi-mode fiber two-channel SPR sensor. In the detection range of the refractive rate between 1.333 RIU and 1.385 RIU, the resonance valley wavelength of channel Ⅰ shifted from 622 nm to 724 nm with a mean average sensitivity of 1961 nm/RIU and the resonance valley wavelength of channel Ⅱ shifted from 741 nm to 976 nm with a mean average sensitivity of 4519 nm/RIU.
Two-channel cryostat for investigation of optical absorption on the UR-20 spectrophotometer
International Nuclear Information System (INIS)
Zhdanovich, N.S.; Kozlov, Yu.I.; Rodkin, E.A.
1977-01-01
A construction of two-channel cryostat for analysing absorption spectra in solids at 300 and 77 K is described. Measurements are made by the differential method. A specimen to be studied is placed in one of the channels and a reference specimen of the same thickness in the other. A spectral dependence of the absorption coefficient of Si alloyed with S has been obtained. Changes in the absorption are due to phototransitions of electrons from various levels of sulphur to the conduction band as the temperature is lowered from 300 to 77 K
Enhancement of dental x-ray images by two channel image processing
International Nuclear Information System (INIS)
Mitra, S.; Yu, T.H.
1991-01-01
In this paper, the authors develop a new algorithm for the enhancement of low-contrast details of dental X-ray images using a two channel structure. The algorithm first decomposes an input image in the frequency domain into two parts by filtering: one containing the low frequency components and the other containing the high frequency components. Then these parts are enhanced separately using a transform magnitude modifier. Finally a contrast enhanced image is formed by combining these two processed pats. The performance of the proposed algorithm is illustrated through enhancement of dental X-ray images. The algorithm can be easily implemented on a personal computer
Plasma streams mixing in two-channel t-shaped magnetic filter
International Nuclear Information System (INIS)
Aksyonov, D.S.; Aksenov, I.I.; Luchaninov, A.A.; Reshetnyak, E.N.; Strel'nitskij, V.E.
2011-01-01
Ti-Al-N films were deposited by vacuum arc method. T-shaped magnetic filter with two channels was used for films preparation. Deposition was performed after aluminum and titanium separate plasma streams from two plasma sources were mixed into single one inside plasma duct having weakened magnetic field near its output. Obtained films have uniform distribution of composition and thickness on 180 mm diameter substrate surface. It was found that mixing and homogenization degree depends on nitrogen pressure, output magnetic field intensity and output- to-substrate distance. Film self-sputtering and aluminum preferential sputtering were observed for elevated negative substrate bias potentials.
Hyperonic mixing in five-baryon double-strangeness hypernuclei in a two-channel treatment
Lanskoy, D. E.; Yamamoto, Y.
2003-01-01
Properties of hypernuclei $_{\\Lambda \\Lambda}^5$H and $_{\\Lambda \\Lambda }^5$He are studied in a two-channel approach with explicit treatment of coupling of channels ^3\\text{Z}+\\Lambda+\\Lambda and \\alpha+\\Xi. Diagonal \\Lambda\\Lambda and coupling \\Lambda\\Lambda-\\Xi N interactions are derived within G-matrix procedure from Nijmegen meson-exchange models. Bond energy \\Delta B_{\\Lambda\\Lambda} in $_{\\Lambda \\Lambda}^5$He exceeds significantly that in $_{\\Lambda \\Lambda}^5$H due to the channel cou...
Experimental studies on heat transfer to supercritical water in 2 × 2 rod bundle with two channels
International Nuclear Information System (INIS)
Gu, H.Y.; Hu, Z.X.; Liu, D.; Xiao, Y.; Cheng, X.
2015-01-01
Highlights: • Heat transfer to supercritical water in a 2 × 2 rod bundle is investigated. • Effects of system parameters on heat transfer in bundle are analyzed. • The test data were compared with twenty heat transfer correlations. - Abstract: The experiment of heat transfer to supercritical water in 2 × 2 rod bundle is performed at Shanghai Jiao Tong University. The test section consists of two channels separated by a square steel assembly box with rounded corners. Water flows downward in the first channel and then turns upward in the second channel to cool the 2 × 2 rod bundle installed inside the assembly box. The bundle consists of four heated rods of 10 mm in O.D. and 1.18 in pitch-to-diameter ratio. The fluid enthalpy in the first channel increases due to the heat transfer through the assembly box when flowing downward. The minimum fluid enthalpy increase in the first channel appears at the pseudo-critical region due to the small temperature difference between the two channels. Effects of various parameters on heat transfer behavior inside the 2 × 2 rod bundle are similar to those observed in tube or annuli. No special phenomenon in heat transfer is observed during the mass flux and power transient. The steady-state heat transfer correlation is applicable to predict the heat transfer in the mass or power transient sequence. In addition, the importance of several dimensionless numbers and the accuracy of 20 heat transfer correlations are assessed. It is concluded that the buoyancy parameter proposed by Cheng et al. (2009) shows unique effect on heat transfer coefficient. Among the 20 selected heat transfer correlations, the correlations of Jackson and Fewster (1975) and Bishop et al. (1964) give the best predictions when compared with the experimental data
A Kondo cluster-glass model for spin glass Cerium alloys
International Nuclear Information System (INIS)
Zimmer, F M; Magalhaes, S G; Coqblin, B
2011-01-01
There are clear indications that the presence of disorder in Ce alloys, such as Ce(Ni,Cu) or Ce(Pd,Rh), is responsible for the existence of a cluster spin glass state which changes continuously into inhomogeneous ferromagnetism at low temperatures. We present a study of the competition between magnetism and Kondo effect in a cluster-glass model composed by a random inter-cluster interaction term and an intra-cluster one, which contains an intra-site Kondo interaction J k and an inter-site ferromagnetic one J 0 . The random interaction is given by the van Hemmen type of randomness which allows to solve the problem without the use of the replica method. The inter-cluster term is solved within the cluster mean-field theory and the remaining intra-cluster interactions can be treated by exact diagonalization. Results show the behavior of the cluster glass order parameter and the Kondo correlation function for several sizes of the clusters, J k , J 0 and values of the ferromagnetic inter-cluster average interaction I 0 . Particularly, for small J k , the magnetic solution is strongly dependent on I 0 and J 0 and a Kondo cluster-glass or a mixed phase can be obtained, while, for large J k , the Kondo effect is still dominant, both in good agreement with experiment in Ce(Ni,Cu) or Ce(Pd,Rh) alloys.
Conductance of closed and open long Aharonov-Bohm-Kondo rings
Shi, Zheng; Komijani, Yashar
2017-02-01
We calculate the finite temperature linear dc conductance of a generic single-impurity Anderson model containing an arbitrary number of Fermi liquid leads, and apply the formalism to closed and open long Aharonov-Bohm-Kondo (ABK) rings. We show that, as with the short ABK ring, there is a contribution to the conductance from the connected four-point Green's function of the conduction electrons. At sufficiently low temperatures this contribution can be eliminated, and the conductance can be expressed as a linear function of the T matrix of the screening channel. For closed rings we show that at temperatures high compared to the Kondo temperature, the conductance behaves differently for temperatures above and below vF/L , where vF is the Fermi velocity and L is the circumference of the ring. For open rings, when the ring arms have both a small transmission and a small reflection, we show from the microscopic model that the ring behaves like a two-path interferometer, and that the Kondo temperature is unaffected by details of the ring. Our findings confirm that ABK rings are potentially useful in the detection of the size of the Kondo screening cloud, the π /2 scattering phase shift from the Kondo singlet, and the suppression of Aharonov-Bohm oscillations due to inelastic scattering.
Fang, Tie-Feng; Guo, Ai-Min; Sun, Qing-Feng
2018-06-01
We investigate Kondo correlations in a quantum dot with normal and superconducting electrodes, where a spin bias voltage is applied across the device and the local interaction U is either attractive or repulsive. When the spin current is blockaded in the large-gap regime, this nonequilibrium strongly correlated problem maps into an equilibrium model solvable by the numerical renormalization group method. The Kondo spectra with characteristic splitting due to the nonequilibrium spin accumulation are thus obtained at high precision. It is shown that while the bias-induced decoherence of the spin Kondo effect is partially compensated by the superconductivity, the charge Kondo effect is enhanced out of equilibrium and undergoes an additional splitting by the superconducting proximity effect, yielding four Kondo peaks in the local spectral density. In the charge Kondo regime, we find a universal scaling of charge conductance in this hybrid device under different spin biases. The universal conductance as a function of the coupling to the superconducting lead is peaked at and hence directly measures the Kondo temperature. Our results are of direct relevance to recent experiments realizing a negative-U charge Kondo effect in hybrid oxide quantum dots [Nat. Commun. 8, 395 (2017), 10.1038/s41467-017-00495-7].
X-boson cumulant approach to the topological Kondo insulators
Ramos, E.; Franco, R.; Silva-Valencia, J.; Foglio, M. E.; Figueira, M. S.
2014-12-01
In this work we present a generalization of our previous work of the X-boson approach to the periodic Anderson model (PAM), adequate to study a novel class of intermetallic 4f and 5f orbitals materials: the topological Kondo insulators, whose paradigmatic material is the compound SmB6. For simplicity, we consider a version of the PAM on a 2D square lattice, adequate to describe Ce-based compounds in two dimensions. The starting point of the model is the 4f - Ce ions orbitals, with J = 5/2 multiplet, in the presence of spin-orbit coupling. Our technique works well for all of the parameters of the model and avoids the unwanted phase transitions of the slave boson mean field theory. We present a critical comparison of our results with those of the usual slave boson method, that has been intensively used to describe this class of materials. We also obtain a new valence first order transition which we attribute to the vec k dependence of the hybridization.
Transport through semiconductor nanowire quantum dots in the Kondo regime
Energy Technology Data Exchange (ETDEWEB)
Schmaus, Stefan; Koerting, Verena; Woelfle, Peter [Institut fuer Theorie der Kondensierten Materie, Universitaet Karlsruhe, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe (Germany)
2008-07-01
Recent experiments on quantum dots made of semiconductor nanowires in the Coulomb blockade regime have shown the influence of several approximately equidistant levels on the conductance. We study a model with three levels occupied by three electrons. At finite bias voltage charge energy conserving excitations into several higher lying states occur leading to features in the differential conductance. We restrict our study to the six lowest lying states by performing a Schrieffer-Wolff type projection onto this subspace. The emerging effective Kondo Hamiltonian is treated in non-equilibrium perturbation theory in the coupling to the leads. For convenience we use a pseudoparticle representation and an exact projection method. The voltage-dependence of the occupation numbers is discussed. The density matrix on the dot turns out to be off-diagonal in the dot eigenstate Hilbert space in certain parameter regimes. The dependence of the differential conductance on magnetic field and temperature is calculated in lowest order in the dot-lead coupling and the results are compared with experiment.
Competition between heavy fermion and Kondo interaction in isoelectronic A-site-ordered perovskites
Energy Technology Data Exchange (ETDEWEB)
Meyers, D.; Middey, S.; Cheng, J. -G.; Mukherjee, Swarnakamal; Gray, B. A.; Cao, Yanwei; Zhou, J. -S.; Goodenough, J. B.; Choi, Yongseong; Haskel, D.; Freeland, J. W.; Saha-Dasgupta, T.; Chakhalian, J.
2014-12-17
With current research efforts shifting towards the 4d and 5d transition metal oxides, understanding the evolution of the electronic and magnetic structure as one moves away from 3d materials is of critical importance. Here we perform X-ray spectroscopy and electronic structure calculations on A-site-ordered perovskites with Cu in the A-site and the B-sites descending along the ninth group of the periodic table to elucidate the emerging properties as d-orbitals change from partially filled 3d to 4d to 5d. The results show that when descending from Co to Ir, the charge transfers from the cuprate-like Zhang-Rice state on Cu to the t2g orbital of the B site. As the Cu d-orbital occupation approaches the Cu2þ limit, a mixed valence state in CaCu3Rh4O12 and heavy fermion state in CaCu3Ir4O12 are obtained. The investigated d-electron compounds are mapped onto the Doniach phase diagram of the competing RKKY and Kondo interactions developed for the f-electron systems.
Chiral helimagnetic state in a Kondo lattice model with the Dzyaloshinskii-Moriya interaction
Okumura, Shun; Kato, Yasuyuki; Motome, Yukitoshi
2018-05-01
Monoaxial chiral magnets can form a noncollinear twisted spin structure called the chiral helimagnetic state. We study magnetic properties of such a chiral helimagnetic state, with emphasis on the effect of itinerant electrons. Modeling a monoaxial chiral helimagnet by a one-dimensional Kondo lattice model with the Dzyaloshinskii-Moriya interaction, we perform a variational calculation to elucidate the stable spin configuration in the ground state. We obtain a chiral helimagnetic state as a candidate for the ground state, whose helical pitch is modulated by the model parameters: the Kondo coupling, the Dzyaloshinski-Moriya interaction, and electron filling.
Global validation of two-channel AVHRR aerosol optical thickness retrievals over the oceans
International Nuclear Information System (INIS)
Liu Li; Mishchenko, Michael I.; Geogdzhayev, Igor; Smirnov, Alexander; Sakerin, Sergey M.; Kabanov, Dmitry M.; Ershov, Oleg A.
2004-01-01
The paper presents validation results for the aerosol optical thickness derived by applying a two-channel retrieval algorithm to Advanced Very High Resolution Radiometer (AVHRR) radiance data. The satellite retrievals are compared with ship-borne sun-photometer results. The comparison of spatial and temporal statistics of the AVHRR results and the ship measurements shows a strong correlation. The satellite retrieval results obtained with the original algorithm for a wavelength of 0.55μm are systematically higher than the sun-photometer measurements in the cases of low aerosol loads. The ensemble averaged satellite-retrieved optical thickness overestimates the ensemble averaged sun-photometer data by about 11% with a random error of about 0.04. Increasing the diffuse component of the ocean surface reflectance from 0.002 to 0.004 in the AVHRR algorithm produces a better match, with the ensemble-averaged AVHRR-retrieved optical thickness differing by only about 3.6% from the sun-photometer truth and having a small offset of 0.03
Peest, Christian; Schinke, Carsten; Brendel, Rolf; Schmidt, Jan; Bothe, Karsten
2017-01-01
Spectrophotometers are operated in numerous fields of science and industry for a variety of applications. In order to provide confidence for the measured data, analyzing the associated uncertainty is valuable. However, the uncertainty of the measurement results is often unknown or reduced to sample-related contributions. In this paper, we describe our approach for the systematic determination of the measurement uncertainty of the commercially available two-channel spectrophotometer Agilent Cary 5000 in accordance with the Guide to the expression of uncertainty in measurements. We focus on the instrumentation-related uncertainty contributions rather than the specific application and thus outline a general procedure which can be adapted for other instruments. Moreover, we discover a systematic signal deviation due to the inertia of the measurement amplifier and develop and apply a correction procedure. Thereby we increase the usable dynamic range of the instrument by more than one order of magnitude. We present methods for the quantification of the uncertainty contributions and combine them into an uncertainty budget for the device.
A high-throughput two channel discrete wavelet transform architecture for the JPEG2000 standard
Badakhshannoory, Hossein; Hashemi, Mahmoud R.; Aminlou, Alireza; Fatemi, Omid
2005-07-01
The Discrete Wavelet Transform (DWT) is increasingly recognized in image and video compression standards, as indicated by its use in JPEG2000. The lifting scheme algorithm is an alternative DWT implementation that has a lower computational complexity and reduced resource requirement. In the JPEG2000 standard two lifting scheme based filter banks are introduced: the 5/3 and 9/7. In this paper a high throughput, two channel DWT architecture for both of the JPEG2000 DWT filters is presented. The proposed pipelined architecture has two separate input channels that process the incoming samples simultaneously with minimum memory requirement for each channel. The architecture had been implemented in VHDL and synthesized on a Xilinx Virtex2 XCV1000. The proposed architecture applies DWT on a 2K by 1K image at 33 fps with a 75 MHZ clock frequency. This performance is achieved with 70% less resources than two independent single channel modules. The high throughput and reduced resource requirement has made this architecture the proper choice for real time applications such as Digital Cinema.
Directory of Open Access Journals (Sweden)
Arjunan Sridhar P.
2015-06-01
Full Text Available This study has investigated the relationship in the connectivity of motor units in surface electromyogram (sEMG of biceps brachii muscle. It is hypothesized that with ageing, there is reduction/loss in number of motor units, leading to reduction in the independence between the channels of the recorded muscle activity. Two channels of sEMG were recorded during three levels of isometric muscle contraction: 50 %, 75 % and 100 % maximal voluntary contraction (MVC. 73 subjects (age range 20-70 participated in the experiments. The independence in channel index (ICI between the two sEMG recording locations was computed using the independent components and Frobenius norm. ANOVA Statistical analysis was performed to test the effect of age (loss of motor units and level of contraction on ICI. The results show that the ICI among the older cohort was significantly lower compared with the younger adults. This research study has shown that the reduction in number of motor units is reflected by the reduction in the ICI of the sEMG signal.
Spin-orbit interaction and asymmetry effects on Kondo ridges at finite magnetic field
DEFF Research Database (Denmark)
Grap, Stephan; Andergassen, Sabine; Paaske, Jens
2011-01-01
ridges, which are robust against SOI as time-reversal symmetry is preserved. As a result of the crossing of a spin-up and a spin-down level at vanishing SOI, two additional Kondo plateaus appear at finite B. They are not protected by symmetry and rapidly vanish if the SOI is turned on. Left......-right asymmetric level-lead couplings and detuned on-site energies lead to a simultaneous breaking of left-right and bonding-antibonding state symmetry. In this case, the finite-B Kondo ridges in the Vg-B plane are bent with respect to the Vg axis. For the Kondo ridge to develop, different level renormalizations......We study electron transport through a serial double quantum dot with Rashba spin-orbit interaction (SOI) and Zeeman field of amplitude B in the presence of local Coulomb repulsion. The linear conductance as a function of a gate voltage Vg equally shifting the levels on both dots shows two B=0 Kondo...
Spin relaxation through Kondo scattering in Cu/Py lateral spin valves
Batley, J. T.; Rosaond, M. C.; Ali, M.; Linfield, E. H.; Burnell, G.; Hickey, B. J.
Within non-magnetic metals it is reasonable to expect the Elliot-Yafet mechanism to govern spin-relaxation and thus the temperature dependence of the spin diffusion length might be inversely proportional to resistivity. However, in lateral spin valves, measurements have found that at low temperatures the spin diffusion length unexpectedly decreases. We have fabricated lateral spin valves from Cu with different concentrations of magnetic impurities. Through temperature dependent charge and spin transport measurements we present clear evidence linking the presence of the Kondo effect within Cu to the suppression of the spin diffusion length below 30 K. We have calculated the spin-relaxation rate and isolated the contribution from magnetic impurities. At very low temperatures electron-electron interactions play a more prominent role in the Kondo effect. Well below the Kondo temperature a strong-coupling regime exists, where the moments become screened and the magnetic dephasing rate is reduced. We also investigate the effect of this low temperature regime (>1 K) on a pure spin current. This work shows the dominant role of Kondo scattering, even in low concentrations of order 1 ppm, within pure spin transport.
Spatial variations of order parameter around Kondo impurity for T<=Tsub(c)
International Nuclear Information System (INIS)
Yoksan, S.
1980-04-01
Analytic expressions for the spatial variations of the order parameter around a Kondo impurity are obtained. The oscillatory contribution due to the impurity scattering is calculated using the t matrix of Matsuura which conveniently yields the general results below Tsub(c). Differences between our values and those of Schlottmann are reported. (author)
Charge dynamics in the Kondo insulator Ce3Bi4Pt3
International Nuclear Information System (INIS)
Bucher, B.; Schlesinger, Z.; Canfield, P.C.; Fisk, Z.
1994-01-01
We report the reflectivity and optical conductivity of the Kondo insulator Ce 3 Bi 4 Pt 3 . For temperatures less than 100 K, depletion of the conductivity below about 300 cm -1 signifies the development of a charge gap. The temperature dependence of the disappearance of the spectral weight scales with the quenching of the Ce 4f moments. ((orig.))
Suppression of the ferromagnetic state by disorder in the Kondo lattice
International Nuclear Information System (INIS)
Crisan, M.; Popoviciu, C.
1992-01-01
This paper reports that ferromagnetic ground state of a Kondo lattice with a low concentration of conduction electrons is ferromagnetic. Assuming the existence of disorder in the Fermi liquid of the conduction electrons the authors show that the ferromagnetic state can be suppressed by the effect of the spin fluctuations of the disordered Fermi liquid
Influence of kondo effect on the specific heat jump of anisotropic superconductors
Yoksan, S.
1986-01-01
A calculation for the specific heat jump of an anisotropic superconductor with Kondo impurities is presented. The impurities are treated within the Matsuura - Ichinose - Nagaoka framework and the anisotropy effect is described by the factorizable model of Markowitz and Kadanoff. We give explicit expressions for the change in specific heat jump due to anisotropy and impurities which can be tested experimentally.
Influence of Kondo effect on the specific heat jump of anisotropic superconductors
International Nuclear Information System (INIS)
Yoksan, S.
1986-01-01
A calculation for the specific heat jump of an anisotropic superconductor with Kondo impurities is presented. The impurities are treated within the Matsuura - Ichinose - Nagaoka framework and the anisotropy effect is described by the factorizable model of Markowitz and Kadanoff. Explicit expressions are given for the change in specific heat jump due to anisotropy and impurities which can be tested experimentally. (author)
DEFF Research Database (Denmark)
Yang, Xi-jun; Qu, Hao; Yao, Chen
2014-01-01
As for high power plasma power supply, due to high efficiency and flexibility, multi-channel interleaved multi-stage paralleled Buck DC-DC Converter becomes the first choice. In the paper, two-channel interleaved two- stage paralleled Buck DC-DC Converter powered by three-phase AC power supply...
International Nuclear Information System (INIS)
Zawadowski, A.; Penc, K.; Zimanyi, G.
1991-07-01
Orbital Kondo effect is treated in a model, where additional to the conduction band there are localized orbitals with energy not very far from the Fermi energy. If the hopping between the conduction band and the localized heavy orbitals depends on the occupation of the conduction band orbital then orbital Kondo correlation occurs. The assisted hopping vertex is enhanced due to the Coulomb interaction between the heavy orbital and the conduction band. The enhanced hopping results in mass enhancement and attractive interaction in the conduction band. The superconductivity transition temperature is calculated. The models of this type can be applied to the high-T c superconductors where the non-bonding oxygen orbitals of the apical oxygens play the role of heavy orbitals. For an essential range of the parameters the T c obtained is about 100K. (author). 22 refs, 9 figs
Two-stage multipolar ordering in Pr T2Al20 Kondo materials
Freyer, Frederic; Attig, Jan; Lee, SungBin; Paramekanti, Arun; Trebst, Simon; Kim, Yong Baek
2018-03-01
Among heavy fermion materials, there is a set of rare-earth intermetallics with non-Kramers Pr3 +4 f2 moments which exhibit a rich phase diagram with intertwined quadrupolar orders, superconductivity, and non-Fermi liquid behavior. However, more subtle broken symmetries such as multipolar orders in these Kondo materials remain poorly studied. Here, we argue that multi-spin interactions between local moments beyond the conventional two-spin exchange must play an important role in Kondo materials near the ordered to heavy Fermi liquid transition. We show that this drives a plethora of phases with coexisting multipolar orders and multiple thermal phase transitions, providing a natural framework for interpreting experiments on the Pr(T) 2Al20 class of compounds.
Evidence for charge Kondo effect in superconducting Tl-doped PbTe
Energy Technology Data Exchange (ETDEWEB)
Fisher, I
2010-01-11
We report results of low-temperature thermodynamic and transport measurements of Pb{sub 1-x}Tl{sub x}Te single crystals for Tl concentrations up to the solubility limit of approximately x = 1.5%. For all doped samples, we observe a low-temperature resistivity upturn that scales in magnitude with the Tl concentration. The temperature and field dependence of this upturn are consistent with a charge Kondo effect involving degenerate Tl valence states differing by two electrons, with a characteristic Kondo temperature T{sub K} {approx} 6 K. The observation of such an effect supports an electronic pairing mechanism for superconductivity in this material and may account for the anomalously high T{sub c} values.
Energy Technology Data Exchange (ETDEWEB)
Strigari, Fabio
2015-04-13
This thesis is mainly focused on the class of Kondo insulators, which also comprises Kondo semiconductors and semimetals. When the right conditions are met - i.e. for a certain number of electrons per unit cell and for certain symmetries of the electronic structure - the interaction between the conduction and f electrons opens a narrow hybridization gap close to the Fermi level. Here we investigate the Kondo semiconductor CeNiSn, as well as the CeM{sub 2}Al{sub 10} compound family with M=Ru, Os and Fe. Many explanations for the low-temperature behavior have been suggested, all of which stress the significance of the 4f crystalline-electric-field (CEF) ground state, which is investigated in the framework of this thesis. We determine the CEF wave functions in this compound family and quantify the degree of c-f hybridization in order to address speculations about the impact of hybridization on the magnetic order. In addition, on the search for parameters which correlate with ground-state properties in heavy-fermion compounds, we investigate the CEF ground states of the intermetallic substitution series CeRh{sub 1-x}Ir{sub x}In{sub 5} since its phase diagram covers all phases of interest, from antiferromagnetic to superconducting as well as regions of phase coexistence. To shed light on the issues above, namely the CEF ground state and the hybridization strength, respectively, two new experimental approaches are used: polarization-dependent X-ray absorption spectroscopy (XAS) and hard X-ray photoelectron spectroscopy (HAXPES). Recently, linearly polarized XAS at the Ce M{sub 4,5} edge has been proven to be highly useful when it comes to the determination of the 4f ground-state wave function in tetragonal rare earth systems. In the present thesis the same technique is applied to the above-mentioned materials, demonstrating that linearly polarized XAS can be employed to obtain an unambiguous and reliable picture of the CEF ground state even in Kondo-insulating systems
Coherence Kondo gap in CeNiSn and CeRhSb
International Nuclear Information System (INIS)
Takabatake, T.; Nakamoto, G.; Tanaka, H.; Bando, Y.; Fujii, H.; Nishigori, S.; Goshima, H.; Suzuki, T.; Fujita, T.; Oguro, I.; Hiraoka, T.; Malik, S.K.
1994-01-01
CeNiSn and CeRhSb are Kondo-lattice compounds showing the behavior of a small-gap semiconductor at temperatures below 7 K. We review and discuss the magnetic, transport and specific-heat measurements performed on single crystals of CeNiSn and polycrystals of CeRhSb. Prerequisites for gap formation are deduced from the effects of substitution and application of a magnetic field and pressure on the gapped state. ((orig.))
Pinchao, Ever Camilo; Kondo, Takumasa; González F., Guillermo
2016-01-01
The Colombian fluted scale (CFS), Crypticerya multicicatrices Kondo & Unruh (Hemiptera: Monophlebidae) is a polyphagous scale insect which affects about 100 species of plants. Between 2010–2013, the species was reported as an invasive pest on the islands of San Andres and Old Providence, Colombian territory in the Caribbean sea. Currently, populations of the CFS also have increased in the city of Cali, Valle del Cauca State, mainland Colombia, affecting different host plants, especially l...
Photoemission and the electronic properties of heavy fermions -- limitations of the Kondo model
International Nuclear Information System (INIS)
Joyce, J.J.; Arko, A.J.; Andrews, A.B.
1993-01-01
The electronic properties of Yb-based heavy fermions have been investigated by means of high resolution synchrotron radiation photoemission and compared with predictions of the Kondo model. The Yb heavy fermion photoemission spectra show massive disagreement with the Kondo model predictions (as calculated within the Gunnarsson-Schonhammer computational method). Moreover, the Yb heavy fermion photoemission spectra give very strong indications of core-like characteristics and compare favorable to purely divalent Yb metal and core-like Lu 4f levels. The heavy fermions YbCu 2 Si 2 , YbAgCu 4 and YbAl 3 were measured and shown to have lineshapes much broader and deeper in binding energy than predicted by the Kondo model. The lineshape of the bulk component of the 4f emission for these three heavy fermion materials was compared with that from Yb metal and the Lu 4f levels in LuAl 3 , the heavy fermion materials show no substantive spectroscopic differences from simple 4f levels observed in Yb metal and LuAl 3 . Also, the variation with temperature of the 4f fineshape was measured for Yb metal and clearly demonstrates that phonon broadening plays a major role in 4f level lineshape analysis and must be accounted for before considerations of correlated electron resonance effects are presumed to be at work
Muon spin relaxation and nonmagnetic Kondo state in PrInAg2
International Nuclear Information System (INIS)
MacLaughlin, D. E.; Heffner, R. H.; Nieuwenhuys, G. J.; Canfield, P. C.; Amato, A.; Baines, C.; Schenck, A.; Luke, G. M.; Fudamoto, Y.; Uemura, Y. J.
2000-01-01
Muon spin relaxation experiments have been carried out in the Kondo compound PrInAg 2 . The zero-field muon relaxation rate is found to be independent of temperature between 0.1 and 10 K, which rules out a magnetic origin (spin freezing or a conventional Kondo effect) for the previously observed specific-heat anomaly at ∼0.5 K. At low temperatures the muon relaxation can be quantitatively understood in terms of the muon's interaction with nuclear magnetism, including hyperfine enhancement of the 141 Pr nuclear moment at low temperatures. This argues against a Pr 3+ ground-state electronic magnetic moment, and is strong evidence for the doublet Γ 3 crystalline-electric-field-split ground state required for a nonmagnetic route to heavy-electron behavior. The data imply the existence of an exchange interaction between neighboring Pr 3+ ions of the order of 0.2 K in temperature units, which should be taken into account in a complete theory of a nonmagnetic Kondo effect in PrInAg 2 . (c) 2000 The American Physical Society
Crossover from 2d to 3d in anisotropic Kondo lattices
International Nuclear Information System (INIS)
Reyes, D.; Continentino, M.A.
2008-01-01
We study the crossover from two to three dimensions in Kondo lattices (KLM) using the Kondo necklace model (KNM). In order to diagonalize the KNM, we use a representation for the localized and conduction electron spins in terms of bond operators and a decoupling for the relevant Green's functions. Both models have a quantum critical point at a finite value of the ratio (J/t) between the Kondo coupling (J) and the hopping (t). In 2d there is no line of finite temperature antiferromagnetic (AF) transitions while for d≥3 this line is given by, T N ∝|g| 1/(d-1) [D. Reyes, M.A. Continentino, Phys. Rev. B 76 (2007) 075114]. The crossover from 2d to 3d is investigated by turning on the electronic hopping (t -perpendicular ) of conduction electrons between different planes. The phase diagram as a function of temperature T, J/t -parallel and ξ=t -perpendicular /t -parallel , where t -parallel is the hopping within the planes is calculated
Pressure dependence of the Curie temperature in the Kondo lattice compound YbNiSn
Energy Technology Data Exchange (ETDEWEB)
Sparn, G; Thompson, J D [Los Alamos National Lab., NM (United States); Hamzic, A [Dept. of Physics, Zagreb (Yugoslavia)
1992-04-03
We have measured the magnetic susceptibility (2 K < T < 300 K) and the electrical resistivity under pressure (1.2 K < T < 300 K; p < 20 kbar) of the Kondo lattice compound YbNiSn, which may be considered as the ''hole'' analogue of the isostructural compound CeNiSn. In contrast with CeNiSn, YbNiSn does not show an energy gap at low temperatures but instead undergoes a magnetic phase transition at T{sub M} = 5.5 K. The magnetic state might be either a weakly ferromagnetic or a complex antiferromagnetic state. By applying pressure the room temperature resistance {rho}{sub RT} decreases, while T{sub M} increases. This behavior can be interpreted with respect to Doniach's Kondo necklace model as a decrease in the local exchange coupling constant J with increasing pressure, which reduces Kondo spin compensation and favors long-range magnetic order. These results show that the idea that YbNiSn is the hole counterpart to CeNiSn holds well for the properties such as dT{sub M}/dP and d{rho}{sub RT}/dP but that it fails in more detailed aspects, such as the origin of the energy gap formation. (orig.).
On the zero-bias anomaly and Kondo physics in quantum point contacts near pinch-off.
Xiang, S; Xiao, S; Fuji, K; Shibuya, K; Endo, T; Yumoto, N; Morimoto, T; Aoki, N; Bird, J P; Ochiai, Y
2014-03-26
We investigate the linear and non-linear conductance of quantum point contacts (QPCs), in the region near pinch-off where Kondo physics has previously been connected to the appearance of the 0.7 feature. In studies of seven different QPCs, fabricated in the same high-mobility GaAs/AlGaAs heterojunction, the linear conductance is widely found to show the presence of the 0.7 feature. The differential conductance, on the other hand, does not generally exhibit the zero-bias anomaly (ZBA) that has been proposed to indicate the Kondo effect. Indeed, even in the small subset of QPCs found to exhibit such an anomaly, the linear conductance does not always follow the universal temperature-dependent scaling behavior expected for the Kondo effect. Taken collectively, our observations demonstrate that, unlike the 0.7 feature, the ZBA is not a generic feature of low-temperature QPC conduction. We furthermore conclude that the mere observation of the ZBA alone is insufficient evidence for concluding that Kondo physics is active. While we do not rule out the possibility that the Kondo effect may occur in QPCs, our results appear to indicate that its observation requires a very strict set of conditions to be satisfied. This should be contrasted with the case of the 0.7 feature, which has been apparent since the earliest experimental investigations of QPC transport.
Energy Technology Data Exchange (ETDEWEB)
Godart, C; Gupta, L C; Tomy, C V; Vijayaraghavan, R; Thompson, J D
1989-02-15
We present the results of our measurements of the lattice constants and magnetic susceptibility of the pseudo-ternary system which crystallizes in the tetragonal ThCr/sub 2/Si/sub 2/ structure. Both of the cell constants a and c increase linearly with x. The magnetic ordering temperature T/sub N/ exhibits initially an enhancement with the increase in x and then decreases as x continues to increase further. These results, along with those on the pressure dependence of T/sub N/ in CeRh/sub 2/Si/sub 2/, can be understood on the basis of the Doniach's model of a Kondo necklace. We discuss also the applicability of this model to describe the strong correlation between the structural aspects and the ground-state properties of the whole series of Ce-based ternaries CeM/sub 2/X/sub 2/ (M = 3d, 4d and 5d elements; X = Si, Ge).
Application of the MIT two-channel model to predict flow recirculation in WARD 61-pin blanket tests
International Nuclear Information System (INIS)
Huang, T.T.; Todreas, N.E.
1983-01-01
The preliminary application of MIT two-channel model to WARD sodium blanket tests was presented in this report. The criterion was employed to predict the recirculation for selected completed (transient and steady state) and proposed (transient only) tests. The heat loss was correlated from the results of the WARD zero power tests. The calculational results show that the criterion agrees with the WARD tests except for WARD RUN 718 for which the criterion predicts a different result from WARD data under bundle heat loss condition. However, if the test assembly is adiabatic, the calculations predict an operating point which is marginally close to the mixed-to-recirculation transition regime
Application of the MIT two-channel model to predict flow recirculation in WARD 61-pin blanket tests
International Nuclear Information System (INIS)
Huang, T.T.; Todreas, N.E.
1983-01-01
The preliminary application of MIT TWO-CHANNEL MODEL to WARD sodium blanket tests was presented in this report. Our criterion was employed to predict the recirculation for selected completed (transient and steady state) and proposed (transient only) tests. The heat loss was correlated from the results of the WARD zero power tests. The calculational results show that our criterion agrees with the WARD tests except for WARD RUN 718 for which the criterion predicts a different result from WARD data under bundle heat loss condition. However, if the test assembly is adiabatic, the calculations predict an operating point which is marginally close to the mixed-to-recirculation transition regime
Reduction of Kondo lattice effects in Yb1-xLuxAl3 observed by soft x-ray photoelectron spectroscopy
International Nuclear Information System (INIS)
Yamaguchi, J; Sekiyama, A; Imada, S; Yamasaki, A; Tsunekawa, M; Muro, T; Ebihara, T; Onuki, Y; Suga, S
2007-01-01
We have carried out the bulk-sensitive and high-resolution soft x-ray photoelectron spectroscopy on Lu substituted intermediate-valence compound Yb 1-x Lu x Al 3 (x = 0.4) at temperatures from 200 to 20 K. The temperature dependences of the bulk Yb 4f photoelectron spectra revealed in our preceding works on high purity YbAl 3 have not been observed in this Lu substituted system. The temperature dependences of the bulk Yb 4f peak positions and the Yb valence in this system can be well reproduced by the single impurity Anderson model (SIAM), whereas the spectral behaviors in YbAl 3 were not at all reproduced by the SIAM. These results confirm the importance of the Kondo lattice effects for YbAl 3 , for which the coherent lattice periodicity plays essential roles
Efimov Physics and the Three-Body Parameter within a Two-Channel Framework
DEFF Research Database (Denmark)
Sørensen, Peder Klokmose; V. Fedorov, D.; S. Jensen, A.
2012-01-01
scaling laws. We recover known results for broad Feshbach resonances with small effective range, whereas in the case of narrow resonances we find a distinct non-monotonic behavior of the threshold at which the lowest Efimov trimer merges with the three-body continuum. To address the issue of the physical...... origin of the three-body parameter we provide a physically clear model for the relation between three-body physics and typical two-body atom-atom interactions. Our results demonstrate that experimental information from narrow Feshbach resonances and/or mixed systems are of vital importance to pin down...... the relation of two- and three-body physics in atomic systems....
Fiber-linked telescope array: description and laboratory tests of a two-channel prototype
Alleman, J. J.; Reynaud, F.; Connes, P.
1995-05-01
We present a complete two-telescope version of a fiber-linked coherent array that is meant to be used for mounting on the dish of a radio telescope. This was built with 20-cm amateur telescopes and includes three different servo subsystems for guiding, nulling of the air path difference, and fiber length control. Laboratory tests of the fully integrated system in front of a star simulator are described.
Directory of Open Access Journals (Sweden)
Masaki Kuwatani
2018-04-01
Full Text Available A 69-year-old woman with jaundice was referred to our hospital. After a final diagnosis of pancreatic cancer with liver metastasis, we performed transpapillary biliary drainage with a covered self-expandable metal stent (SEMS. Three months later, we also placed an uncovered duodenal stent for duodenal stricture in a side-to-end fashion. Another month later, for biliary SEMS obstruction, we attempted a transpapillary approach. A duodenoscope was advanced and a guidewire was passed through the mesh of the duodenal stent into the bile duct with a flexible tip catheter, but the catheter was not. Thus, we exchanged the duodenoscope for a forward-viewing two-channel endoscope and used the left working channel with a flexible tip catheter. By adjusting the axis, we finally succeeded biliary cannulation and accomplished balloon cleaning for recanalization of the SEMS. This is the first case with successful biliary cannulation by combined use of a two-channel endoscope and a flexible tip catheter.
International Nuclear Information System (INIS)
Shimada, K.; Arita, M.; Takeda, Y.; Namatame, H.; Taniguchi, M.; Higashiguchi, M.; Oguchi, T.; Sasakawa, T.; Suemitsu, T.; Takabatake, T.
2004-01-01
Full text: The orthorhombic CeRhAs, known as a Kondo semiconductor, has attracted much interest for its unusual energy-gap formation associated with the successive 1st order phase transitions. In order to elucidate the mechanism of the energy- gap formation, we have done high-resolution temperature-dependent photoemission spectroscopy on the undulator beamlines of a compact electron-storage ring, HiSOR, at Hiroshima University. We have observed directly the energy-gap formation in the Ce 4f states and in the conduction bands. Comparing with the isostructural Kondo semimetal CeRhSb, we discuss the energy gap formation in CeRhAs
Schwingenschlö gl, Udo; Shelykh, I. A.
2009-01-01
We consider the magnetic interaction of manganese phtalocyanine (MnPc) absorbed on Pb layers that were grown on a Si substrate. We perform an ab initio calculation of the density of states and Kondo temperature as a function of the number of Pb monolayers. Comparison to experimental data [Y.-S. Fu et al., Phys. Rev. Lett. 99, 256601 (2007)] then allows us to determine the exchange coupling constant J between the spins of the adsorbed molecules and those of the Pb host. This approach gives rise to a general and reliable method for obtaining J by combining experimental and numerical results.
Nonlinear susceptibility: A direct test of the quadrupolar Kondo effect in UBe13
International Nuclear Information System (INIS)
Ramirez, A.P.; Chandra, P.; Coleman, P.; Fisk, Z.; Smith, J.L.; Ott, H.R.
1994-01-01
We present the nonlinear susceptibility as a direct test of the quadrupolar Kondo scenario for heavy fermion behavior, and apply it to the case of cubic crystal-field symmetry. Within a single-ion model we compute the nonlinear susceptibility resulting from low-lying Γ 3 (5f 2 ) and Kramers (5f 3 ) doublets. We find that nonlinear susceptibility measurements on single-crystal UBe 13 are inconsistent with a quadrupolar (5f 2 ) ground state of the uranium ion; the experimental data indicate that the low-lying magnetic excitations of UBe 13 are predominantly dipolar in character
Principle-theoretic approach of kondo and construction-theoretic formalism of gauge theories
International Nuclear Information System (INIS)
Jain, L.C.
1986-01-01
Einstein classified various theories in physics as principle-theories and constructive-theories. In this lecture Kondo's approach to microscopic and macroscopic phenomena is analysed for its principle theoretic pursuit as followed by construction. The fundamentals of his theory may be recalled as Tristimulus principle, Observation principle, Kawaguchi spaces, empirical information, epistemological point of view, unitarity, intrinsicality, and dimensional analysis subject to logical and geometrical achievement. On the other hand, various physicists have evolved constructive gauge theories through the phenomenological point of view, often a collective one. Their synthetic method involves fibre bundles and connections, path integrals as well as other hypothetical structures. They lead towards clarity, completeness and adaptability
Kondo resonance in the neutron spectra of intermediate-valent YbAl3
International Nuclear Information System (INIS)
Walter, U.; Holland-Moritz, E.; Fisk, Z.
1991-01-01
We have measured the dynamic susceptibility of intermediate-valent YbAl 3 by means of cold-neutron scattering. We find two intense magnetic excitations below 40 meV. One of these, with location around 18 meV at helium temperatures, shifts steadily toward 0 meV with increasing temperatures. While crystal field interactions are unable to account for such a behavior, this excitation is in good agreement with a transition from the f ground state to a Kondo resonance as described by the Anderson model. In particular, it definitely excludes a gaplike magnetic response with gap width Δ=30 meV as asserted earlier
A low-temperature derivation of spin-spin exchange in Kondo lattice model
International Nuclear Information System (INIS)
Feng Szeshiang; Mochena, Mogus
2005-01-01
Using Hubbard-Stratonovich transformation and drone-fermion representations for spin-12 and for spin-32, which is presented for the first time, we make a path-integral formulation of the Kondo lattice model. In the case of weak coupling and low temperature, the functional integral over conduction fermions can be approximated to the quadratic order and this gives the well-known RKKY interaction. In the case of strong coupling, the same quadratic approximation leads to an effective local spin-spin interaction linear in hopping energy t
A low-temperature derivation of spin-spin exchange in Kondo lattice model
Energy Technology Data Exchange (ETDEWEB)
Feng Szeshiang [Physics Department, Florida A and M University, Tallahassee, FL 32307 (United States)]. E-mail: shixiang.feng@famu.edu; Mochena, Mogus [Physics Department, Florida A and M University, Tallahassee, FL 32307 (United States)
2005-11-01
Using Hubbard-Stratonovich transformation and drone-fermion representations for spin-12 and for spin-32, which is presented for the first time, we make a path-integral formulation of the Kondo lattice model. In the case of weak coupling and low temperature, the functional integral over conduction fermions can be approximated to the quadratic order and this gives the well-known RKKY interaction. In the case of strong coupling, the same quadratic approximation leads to an effective local spin-spin interaction linear in hopping energy t.
Schwingenschlögl, Udo
2009-07-01
We consider the magnetic interaction of manganese phtalocyanine (MnPc) absorbed on Pb layers that were grown on a Si substrate. We perform an ab initio calculation of the density of states and Kondo temperature as a function of the number of Pb monolayers. Comparison to experimental data [Y.-S. Fu et al., Phys. Rev. Lett. 99, 256601 (2007)] then allows us to determine the exchange coupling constant J between the spins of the adsorbed molecules and those of the Pb host. This approach gives rise to a general and reliable method for obtaining J by combining experimental and numerical results.
Evidence of two-channel distortion effects in positronium formation reactions
International Nuclear Information System (INIS)
Macri, P A; Miraglia, J E; Hanssen, J; Fojon, O A; Rivarola, R D
2004-01-01
The formation of ground-state positronium in collisions of positrons on hydrogen-like atoms is considered. In previous theoretical works, two-centre distorted wavefunctions were employed to approximate either the initial or the final channel. Here we report results obtained by means of the eikonal final state continuum distorted wave approximation for which asymptotically correct distorted wavefunctions are used for both the initial and final states of the scattering system. Comparison of the present theoretical total cross sections with experimental data reveals that distortion effects become important in both channels as the impact energy decreases. This work also shows that distorted-wave theories may be extended from their usual domain of high impact energies to lower ones. (letter to the editor)
Evidence of two-channel distortion effects in positronium formation reactions
Energy Technology Data Exchange (ETDEWEB)
Macri, P A [Instituto de AstronomIa y FIsica del Espacio, Consejo Nacional de Investigaciones CientIficas y Tecnicas-Universidad de Buenos Aires, Casilla de Correo 67, Suc. 28, 1428 Buenos Aires (Argentina); Miraglia, J E [Instituto de AstronomIa y FIsica del Espacio, Consejo Nacional de Investigaciones CientIficas y Tecnicas-Universidad de Buenos Aires, Casilla de Correo 67, Suc. 28, 1428 Buenos Aires (Argentina); Hanssen, J [Laboratoire de Physique Moleculaire et des Collisions, Institute de Physique Rue Arago, Tecnopole 2000, Metz (France); Fojon, O A [Instituto de FIsica de Rosario, Consejo Nacional de Investigaciones CientIficas y Tecnicas-Universidad Nacional de Rosario, Av. Pellegrini 250, 2000 Rosario (Argentina); Rivarola, R D [Instituto de FIsica de Rosario, Consejo Nacional de Investigaciones CientIficas y Tecnicas-Universidad Nacional de Rosario, Av. Pellegrini 250, 2000 Rosario (Argentina)
2004-03-28
The formation of ground-state positronium in collisions of positrons on hydrogen-like atoms is considered. In previous theoretical works, two-centre distorted wavefunctions were employed to approximate either the initial or the final channel. Here we report results obtained by means of the eikonal final state continuum distorted wave approximation for which asymptotically correct distorted wavefunctions are used for both the initial and final states of the scattering system. Comparison of the present theoretical total cross sections with experimental data reveals that distortion effects become important in both channels as the impact energy decreases. This work also shows that distorted-wave theories may be extended from their usual domain of high impact energies to lower ones. (letter to the editor)
Magnetic impurity in a system of interacting electrons
International Nuclear Information System (INIS)
Huynh Thanh Duc; Nguyen Toan Thang
1999-04-01
The Kondo effect of the Anderson impurity in a correlated conduction electron system is studied within the slave boson mean-field theory. The interacting conduction electrons are described by a Hubbard model with an interaction of strength U. It is shown that the Kondo temperature T K decreases with an increase of U. In the intermediate regime at half-filling the exponential scale of the Kondo temperature T K is lost already at the saddle-point level of slave boson formulation. (author)
DuOCam: A Two-Channel Camera for Simultaneous Photometric Observations of Stellar Clusters
Maier, Erin R.; Witt, Emily; Depoy, Darren L.; Schmidt, Luke M.
2017-01-01
We have designed the Dual Observation Camera (DuOCam), which uses commercial, off-the-shelf optics to perform simultaneous photometric observations of astronomical objects at red and blue wavelengths. Collected light enters DuOCam’s optical assembly, where it is collimated by a negative doublet lens. It is then separated by a 45 degree blue dichroic filter (transmission bandpass: 530 - 800 nm, reflection bandpass: 400 - 475 nm). Finally, the separated light is focused by two identical positive doublet lenses onto two independent charge-coupled devices (CCDs), the SBIG ST-8300M and the SBIG STF-8300M. This optical assembly converts the observing telescope to an f/11 system, which balances maximum field of view with optimum focus. DuOCam was commissioned on the McDonald Observatory 0.9m, f/13.5 telescope from July 21st - 24th, 2016. Observations of three globular and three open stellar clusters were carried out. The resulting data were used to construct R vs. B-R color magnitude diagrams for a selection of the observed clusters. The diagrams display the characteristic evolutionary track for a stellar cluster, including the main sequence and main sequence turn-off.
Bladder cancer treatment response assessment in CT urography using two-channel deep-learning network
Cha, Kenny H.; Hadjiiski, Lubomir M.; Chan, Heang-Ping; Samala, Ravi K.; Cohan, Richard H.; Caoili, Elaine M.; Weizer, Alon Z.; Alva, Ajjai
2018-02-01
We are developing a CAD system for bladder cancer treatment response assessment in CT. We trained a 2- Channel Deep-learning Convolution Neural Network (2Ch-DCNN) to identify responders (T0 disease) and nonresponders to chemotherapy. The 87 lesions from 82 cases generated 18,600 training paired ROIs that were extracted from segmented bladder lesions in the pre- and post-treatment CT scans and partitioned for 2-fold cross validation. The paired ROIs were input to two parallel channels of the 2Ch-DCNN. We compared the 2Ch-DCNN with our hybrid prepost- treatment ROI DCNN method and the assessments by 2 experienced abdominal radiologists. The radiologist estimated the likelihood of stage T0 after viewing each pre-post-treatment CT pair. Receiver operating characteristic analysis was performed and the area under the curve (AUC) and the partial AUC at sensitivity AUC0.9) were compared. The test AUCs were 0.76+/-0.07 and 0.75+/-0.07 for the 2 partitions, respectively, for the 2Ch-DCNN, and were 0.75+/-0.08 and 0.75+/-0.07 for the hybrid ROI method. The AUCs for Radiologist 1 were 0.67+/-0.09 and 0.75+/-0.07 for the 2 partitions, respectively, and were 0.79+/-0.07 and 0.70+/-0.09 for Radiologist 2. For the 2Ch-DCNN, the AUC0.9s were 0.43 and 0.39 for the 2 partitions, respectively, and were 0.19 and 0.28 for the hybrid ROI method. For Radiologist 1, the AUC0.9s were 0.14 and 0.34 for partition 1 and 2, respectively, and were 0.33 and 0.23 for Radiologist 2. Our study demonstrated the feasibility of using a 2Ch-DCNN for the estimation of bladder cancer treatment response in CT.
Magnetic and orbital instabilities in a lattice of SU(4) organometallic Kondo complexes
International Nuclear Information System (INIS)
Lobos, A M; Aligia, A A
2014-01-01
Motivated by experiments of scanning tunneling spectroscopy (STS) on self- assembled networks of iron(II)-phtalocyanine (FePc) molecules deposited on a clean Au(111) surface [FePc/Au(111)] and its explanation in terms of the extension of the impurity SU(4) Anderson model to the lattice in the Kondo regime, we study the competition between the Kondo effect and the magneto-orbital interactions occurring in FePc/Au(111). We explore the quantum phases and critical points of the model using a large-N slave-boson method in the mean-field approximation. The SU(4) symmetry in the impurity appears as a combination of the usual spin and an orbital pseudospin arising from the degenerate 3d xz and 3d yz orbitals in the Fe atom. In the case of the lattice, our results show that the additional orbital degrees of freedom crucially modify the low-temperature phase diagram, and induce new types of orbital interactions among the Fe atoms, which can potentially stabilize exotic quantum phases with magnetic and orbital order. The dominant instability corresponds to spin ferromagnetic and orbital antiferromagnetic order
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
Magnetic order and Kondo effect in the Anderson-lattice model
International Nuclear Information System (INIS)
Bernhard, B.H.; Aguiar, C.; Kogoutiouk, I.; Coqblin, B.
2007-01-01
The Anderson-lattice model has been extensively developed to account for the properties of many anomalous rare-earth compounds and in particular for the competition between the Kondo effect and an antiferromagnetic (AF) phase in a cubic lattice. Here we apply the higher-order decoupling of the equations of motion for the Green Functions (GF) introduced in [H.G. Luo, S.J. Wang, Phys. Rev. B 62 (2000) 1485]. We obtain an improved description of the phase diagram, where the AF phase subsists in a smaller range of the model parameters. As higher-order GF are included in the chain of equations, we are able to calculate directly the local spin-flip correlation function † ↓ d † ↑ f ↑ d ↓ >. As a further improvement to the previous approximation of [B.H. Bernhard, C. Aguiar, B. Coqblin, Physica B 378-380 (2006) 712], we obtain a reduced range of existence for the AF phase for the symmetric half-filled case and then we discuss the competition between the AF order and the Kondo effect as a function of the band filling
Accidental cloning of a single-photon qubit in two-channel continuous-variable quantum teleportation
International Nuclear Information System (INIS)
Ide, Toshiki; Hofmann, Holger F.
2007-01-01
The information encoded in the polarization of a single photon can be transferred to a remote location by two-channel continuous-variable quantum teleportation. However, the finite entanglement used in the teleportation causes random changes in photon number. If more than one photon appears in the output, the continuous-variable teleportation accidentally produces clones of the original input photon. In this paper, we derive the polarization statistics of the N-photon output components and show that they can be decomposed into an optimal cloning term and completely unpolarized noise. We find that the accidental cloning of the input photon is nearly optimal at experimentally feasible squeezing levels, indicating that the loss of polarization information is partially compensated by the availability of clones
Spin-Orbit Interaction and Kondo Scattering at the PrAlO3/SrTiO3 Interface
Mozaffari, Shirin; Guchhait, Samaresh; Markert, John
We have investigated the effect of oxygen content, in the PO2 range of 6 ×10-6 - 1 ×10-3 torr, on the spin-orbit (SO) interaction at PrAlO3/SrTiO3 interface. The most-conducting 2-D-like PrAlO3 interfaces were not as conducting as comparable LaAlO3 samples, indicating either a steric or mixed-valent effect. The least-conducting, most oxygenated PrAlO3 interface exhibits hole conductivity, a departure from the typical electron-doped behavior. For 10-5 and 10-4 torr samples, high-temperature metallic behavior is accompanied by an upturn in resistivity at low temperatures, consistent with Kondo scattering theory; analysis gives a Kondo temperature 17 K. The magnetoresistance (MR) for the low PO2-grown samples was modeled with a positive part due to weak anti-localization (WAL) from a strong SO interaction, and a negative part due to the Kondo effect. The variation of MR suggests a strong SO interaction for the 10-5 torr sample with HSO = 1.25 T in both field orientations. The WAL effect is smaller for higher PO2-grown samples, where the high-field MR is dominated by the Kondo effect.
International Nuclear Information System (INIS)
van Dongen, J.C.M.; van Dijk, D.; Mydosh, J.A.
1981-01-01
Through low-field ac susceptibility measurements we have determined the depression of the superconducting transition temperature T/sub c/ in palladium hydride (T/sub c/0 = 9.3 K) as a function of impurity concentration x for Cr, Mn, and Fe. For Cr and Fe similar values for the initial T/sub c/ depression were found, i.e., -150 K/at. % Cr and -145 K/at. % Fe. From resistivity experiments we are able to estimate the Kondo temperatures T/sub K/, i.e., T/sub K/approx. =10 K for Cr and T/sub K/approx. =5 K for Fe. Since i.e., T/sub K/approx. =10 K for Cr and T/sub K/approx. =5 K for Fe. Since systems exhibits an enhanced pair breaking as described by the theory of Mueller-Hartmann and Zittartz. In contrast, for Mn the initial T/sub c/ depression is -21 K/at. % and T/sub K/<< T/sub c/0, as can be concluded from our resistivity measurements. This means that Mn in PdH exhibits a temperature-independent pair breaking of the Abrikosov and Gor'kov type. However, at larger Mnx values a shoulder appears in T/sub c/(x). We interpret this enhanced superconductivity, according to the theory of Soukoulis and Grest, as being due to the onset of time correlations and short-range antiferromagnetic ordering between the Mn moments. These interaction effects are a precursor to the spin-glass freezing at a lower temperature T/sub f/. Our results suggest a favorable coexistance of superconductivity with the spin-glass state
Neutron diffraction study of dense-Kondo compound CeNi2Al5
International Nuclear Information System (INIS)
Munoz, A.; Givord, F.; Boucherie, J.X.; Flouquet, J.; Isikawa, Y.; Mizushima, T.; Sakurai, J.; Mori, K.; Oliveira, I.S.
1993-01-01
Intermetallic CeNi 2 Al 5 is a dense-Kondo compound with a magnetic transition temperature at 2.6 K. We have carried out a neutron diffraction measurement to study a magnetic structure of CeNi 2 Al 5 using a powder sample and a single crystalline sample. It is found that the magnetic structure is an incommensurate sinusoidal one with a propagation vector k = (0.5, 0.405, 0.083) and that the amplitude of magnetic moment is 1.54 μ Β and the direction of magnetic moment is declined 8 deg. from the b-axis toward the a-axis. (authors). 3 refs., 2 figs
Landau quantization and spin-momentum locking in topological Kondo insulators
Directory of Open Access Journals (Sweden)
P. Schlottmann
2016-05-01
Full Text Available SmB6 has been predicted to be a strong topological Kondo insulator and experimentally it has been confirmed that at low temperatures the electrical conductivity only takes place at the surfaces of the crystal. Quantum oscillations and ARPES measurements revealed several Dirac cones on the (001 and (101 surfaces of the crystal. We considered three types of surface Dirac cones with an additional parabolic dispersion and studied their Landau quantization and the expectation value of the spin of the electrons. The Landau quantization is quite similar in all three cases and would give rise to very similar de Haas-van Alphen oscillations. The spin-momentum locking, on the other hand, differs dramatically. Without the additional parabolic dispersion the spins are locked in the plane of the surface. The parabolic dispersion, however, produces a gradual canting of the spins out of the surface plane.
Transport properties of the topological Kondo insulator SmB6 under the irradiation of light
International Nuclear Information System (INIS)
Zhu Guo-Bao; Yang Hui-Min
2016-01-01
In this paper, we study transport properties of the X point in the Brillouin zone of the topological Kondo insulator SmB 6 under the application of a circularly polarized light. The transport properties at high-frequency regime and low-frequency regime as a function of the ratio ( κ ) of the Dresselhaus-like and Rashba-like spin–orbit parameter are studied based on the Floquet theory and Boltzmann equation respectively. The sign of Hall conductivity at high-frequency regime can be reversed by the ratio κ and the amplitude of the light. The amplitude of the current can be enhanced by the ratio κ . Our findings provide a way to control the transport properties of the Dirac materials at low-frequency regime. (paper)
Different magnetic behaviour of the Kondo compounds Al3Ce and Al11Ce3
International Nuclear Information System (INIS)
Benoit, A.; Flouquet, J.; Palleau, J.; Buevoz, J.L.
1979-08-01
Neutron diffraction experiments on the Al 3 Ce and Al 11 Ce 3 compounds have been performed on the multidetector of the I.L.L. high flux reactor. No magnetic structure has been detected on the Al 3 Ce compound down to 20 mK. This confirms the non magnetic ground state of Al 3 Ce. For Al 11 Ce 3 , two magnetic structures have been observed: a ferromagnetic one at 4.2 K and an antiferromagnetic one at 2 K. The antiferromagnetic structure, which corresponds to a propagation vector (0,0,1/3), implies a strong reduction of the magnetic moment of determined sites; this reflects the Kondo character of the compounds
Energy Technology Data Exchange (ETDEWEB)
Ernst, Stefan
2011-06-24
in the framework of this thesis different heavy-fermion systems were studied by means of scanning tunneling microscopy and spectroscopy. In the experiment two main topics existed. On the one hand the heavy-fermion superconductivity in the compounds CeCu{sub 2}Si{sub 2}, CeCoIn{sub 5}, and on the other hand the Kondo effect in the Kondo-lattice system YbRh{sub 2}Si{sub 2}.
International Nuclear Information System (INIS)
Dashti, Mohsen; Rasouli, Saifollah
2012-01-01
Recently, an adjustable, high-sensitivity, wide dynamic range, two-channel wavefront sensor based on moiré deflectometry was proposed by Rasouli et al (2010 Opt. Express 18 23906). In this work we have used this sensor on a telescope for measuring turbulence-induced wavefront distortions. A slightly divergent laser beam passes through turbulent ground level atmosphere and enters the telescope’s aperture. The laser beam is collimated behind the telescope’s focal point by means of a collimator and the beam enters the wavefront sensor. First, from deviations in the moiré fringes we calculate the two orthogonal components of the angle of arrival at each location across the wavefront. The deviations have been deduced in successive frames which allows evolution of the wavefront shape and Fried’s seeing parameter r 0 to be determined. Mainly, statistical analysis of the reconstructed wavefront distortions are presented. The achieved accuracy in the measurements and comparison between the measurements and the theoretical models are presented. Owing to the use of the sensor on a telescope, and using sub-pixel accuracy for the measurement of the moiré fringe displacements, the sensitivity of the measurements is improved by more than one order of magnitude. In this work we have achieved a minimum measurable angle of arrival fluctuations equal to 3.7 × 10 −7 rad or 0.07 arc s. Besides, because of the large area of the telescope’s aperture, a high spatial resolution is achieved in detecting the spatial perturbations of the atmospheric turbulence. (paper)
An evaluation of two-channel ChIP-on-chip and DNA methylation microarray normalization strategies
2012-01-01
Background The combination of chromatin immunoprecipitation with two-channel microarray technology enables genome-wide mapping of binding sites of DNA-interacting proteins (ChIP-on-chip) or sites with methylated CpG di-nucleotides (DNA methylation microarray). These powerful tools are the gateway to understanding gene transcription regulation. Since the goals of such studies, the sample preparation procedures, the microarray content and study design are all different from transcriptomics microarrays, the data pre-processing strategies traditionally applied to transcriptomics microarrays may not be appropriate. Particularly, the main challenge of the normalization of "regulation microarrays" is (i) to make the data of individual microarrays quantitatively comparable and (ii) to keep the signals of the enriched probes, representing DNA sequences from the precipitate, as distinguishable as possible from the signals of the un-enriched probes, representing DNA sequences largely absent from the precipitate. Results We compare several widely used normalization approaches (VSN, LOWESS, quantile, T-quantile, Tukey's biweight scaling, Peng's method) applied to a selection of regulation microarray datasets, ranging from DNA methylation to transcription factor binding and histone modification studies. Through comparison of the data distributions of control probes and gene promoter probes before and after normalization, and assessment of the power to identify known enriched genomic regions after normalization, we demonstrate that there are clear differences in performance between normalization procedures. Conclusion T-quantile normalization applied separately on the channels and Tukey's biweight scaling outperform other methods in terms of the conservation of enriched and un-enriched signal separation, as well as in identification of genomic regions known to be enriched. T-quantile normalization is preferable as it additionally improves comparability between microarrays. In
Directory of Open Access Journals (Sweden)
Romain Maurand
2012-02-01
Full Text Available We study a carbon-nanotube quantum dot embedded in a superconducting-quantum-interference-device loop in order to investigate the competition of strong electron correlations with a proximity effect. Depending on whether local pairing or local magnetism prevails, a superconducting quantum dot will exhibit a positive or a negative supercurrent, referred to as a 0 or π Josephson junction, respectively. In the regime of a strong Coulomb blockade, the 0-to-π transition is typically controlled by a change in the discrete charge state of the dot, from even to odd. In contrast, at a larger tunneling amplitude, the Kondo effect develops for an odd-charge (magnetic dot in the normal state, and quenches magnetism. In this situation, we find that a first-order 0-to-π quantum phase transition can be triggered at a fixed valence when superconductivity is brought in, due to the competition of the superconducting gap and the Kondo temperature. The superconducting-quantum-interference-device geometry together with the tunability of our device allows the exploration of the associated phase diagram predicted by recent theories. We also report on the observation of anharmonic behavior of the current-phase relation in the transition regime, which we associate with the two accessible superconducting states. Our results finally demonstrate that the spin-singlet nature of the Kondo state helps to enhance the stability of the 0 phase far from the mixed-valence regime in odd-charge superconducting quantum dots.
Watanabe, K; Kanadani, C; Taniguchi, T; Kawarazaki, S; Uwatoko, Y; Kadowaki, H
2003-01-01
Neutron diffraction experiments have been carried out to study the nature of the magnetic order of the pseudo-binary alloy system Ce(Ru sub 0 sub . sub 9 sub 0 Rh sub 0 sub . sub 1 sub 0) sub 2 (Si sub 1 sub - sub y Ge sub y) sub 2. Response of the ordered atomic magnetic moment, mu, the transition temperature, T sub N , and the magnitude of the magnetic modulation vector, q, to the chemical pressure and also to the applied hydrostatic pressure, P, were examined at low temperatures. When y changes, all of mu, T sub N and q show a sudden alteration of the manner of the y-dependence at around y - 0.08. The P-dependence of q shows quite different features for different y's of 0.0, 0.2 and 0.25. On the basis of these observations the possibility of a pressure-induced alternation of the magnetic regime of the order is discussed. (author)
Interaction-driven sub-gap resonance in the topological Kondo insulator SmB6
Fuhrman, Wesley
2015-03-01
Samarium hexaboride (SmB6) is a strongly correlated Kondo Insulator with a non-trivial band-structure topology. I will discuss recent neutron scattering experiments and analysis that expose a 14 meV resonant mode in SmB6 and relate it to the low energy insulating band structure. Repeating outside the first Brillouin zone, the mode is coherent with a 5 d-like magnetic form factor. I will discuss how band inversion can be inferred from neutron scattering and show that a perturbative slave boson treatment of a hybridized 2 species (d/ f) band structure within an Anderson model can produce a spin exciton with the observed characteristics. This analysis provides a detailed physical picture of how the SmB6 band topology arises from strong electron interactions, and accounts for the 14 meV resonant mode as a magnetically active exciton. The work at IQM was supported by the US Department of Energy, office of Basic Energy Sciences, Division of Material Sciences and Engineering under Grant DE-FG02-08ER46544.
Magnetic Doping and Kondo Effect in Bi 2 Se 3 Nanoribbons
Cha, Judy J.; Williams, James R.; Kong, Desheng; Meister, Stefan; Peng, Hailin; Bestwick, Andrew J.; Gallagher, Patrick; Goldhaber-Gordon, David; Cui, Yi
2010-01-01
A simple surface band structure and a large bulk band gap have allowed Bi2Se3 to become a reference material for the newly discovered three-dimensional topological insulators, which exhibit topologically protected conducting surface states that reside inside the bulk band gap. Studying topological insulators such as Bi2Se3 in nanostructures is advantageous because of the high surfaceto-volume ratio, which enhances effects from the surface states; recently reported Aharonov-Bohm oscillation in topological insulator nanoribbons by some of us is a good example. Theoretically, introducing magnetic impurities in topological insulators is predicted to open a small gap in the surface states by breaking time-reversal symmetry. Here, we present synthesis of magnetically doped Bi 2Se3 nanoribbons by vapor-liquid-solid growth using magnetic metal thin films as catalysts. Although the doping concentration is less than ∼2 %. low-temperature transport measurements of the Fe-doped Bi2Se3 nanoribbon devices show a clear Kondo effect at temperatures below 30 K, confirming the presence of magnetic impurities in the Bi2Se3 nanoribbons. The capability to dope topological insulator nanostructures magnetically opens up exciting opportunities for spintronics. © 2010 American Chemical Society.
NMR of Cu satellites in the Kondo alloy CuCr
International Nuclear Information System (INIS)
Azevedo, L.J.; Follstaedt, D.; Narath, A.
1978-01-01
Using pulsed NMR techniques, resonances of Cu nuclei which are near neighbors to Cr impurities (c = 100 and 200 ppM) in CuCr (theta/sub k/ approx. 3K) have been studied in the temperature range 1 to 4K and applied fields H 0 = 20 to 125 kOe. At the highest fields and lowest temperatures the satellite shifts approach saturation. Above approx. 40 kOe the spin-lattice relaxation rate T 1 -1 is proportional to T/H 0 2 , indicating that the dominant relaxation mechanism arises from transverse fluctuations of a polarized local moment. The measured rates yield a local-moment/conduction-electron exchange interaction vertical bar J 0 vertical bar/g = 0.30, where g is the Cr g-value. Below approx. 40 kOe T 1 -1 appears to be slightly enhanced in comparison with the high-field behavior, but becomes field independent below approx. 30 kOe. Both effects are attributed to Kondo anomalies
Quenching of orbital momentum by crystalline fields in a multichannel Kondo impurity
International Nuclear Information System (INIS)
Schlottmann, P.; Lee, K.
1995-01-01
We consider an impurity of spin S interacting via an isotropic spin exchange with conduction electrons of spin 1/2. The conduction electrons can be in n different orbital channels. We assume that crystalline fields split the orbital degrees of freedom into two multiplets, the one with lower energy consisting of n * orbitals and the one of higher energy of n-n * orbitals. The exchange coupling is the same for all channels. We derive the thermodynamic Bethe ansatz equations for this model and discuss the ground-state properties of the impurity as a function of the spin S and the magnetic field. The solution of the ground-state Bethe ansatz equations is obtained numerically. Three situations have to be distinguished when the magnetic field is small compared to the Kondo temperature: (i) If S=n/2 or S=n * /2 the conduction electrons exactly compensate the impurity spin into a singlet ground state, (ii) if S>n/2 the impurity is undercompensated, i.e., only partially compensated leaving an effective spin S-n/2 at low temperatures, and (iii) in all other cases the impurity spin is overcompensated giving rise to critical behavior. The quenching of the orbits by the crystalline field dramatically affects the cases S * /2
Effects of magnetic field on the pseudogap in the Kondo semiconductor CeRhAs
International Nuclear Information System (INIS)
Yoshii, S.; Kindo, K.; Sasakawa, T.; Suemitsu, T.; Takabatake, T.
2004-01-01
The magnetization and magnetoresistance of single-crystalline CeRhAs, which is the so-called Kondo semiconductor with an energygap of ∼280 K, have been measured in pulsed magnetic field up to 55 T. At 1.3 K, the slopes of the magnetization M for H parallel b and H parallel c decrease slightly at around 16 and 13 T, respectively, while M(H parallel a) shows monotonous dependence. Weak anisotropy is observed on the whole, M b (H)>M c (H)>M a (H). M b (H) reaches only to 0.07 μ B /f.u. at 55 T, which indicates the non-magnetic state being stable even in the high magnetic field. Strongly anisotropic behaviors are observed in the magnetoresistance. The longitudinal magnetoresistance (LMR) along the b- and c-axis show characteristic structures partly associated with the anomalies of the magnetizations, while the LMR along the a-axis shows only a broad maximum. The transverse magnetoresistances (TMR) for I parallel b and I parallel c follow the relation Δρ(H)/ρ(0)∝H α (α=1.5-1.7) below 5 T, whereas TMR for I parallel a exhibits only the weak field dependence. These results suggest the existence of a narrow and anisotropic structure within the wide pseudogap structure in the density of states
Magnetic Doping and Kondo Effect in Bi 2 Se 3 Nanoribbons
Cha, Judy J.
2010-03-10
A simple surface band structure and a large bulk band gap have allowed Bi2Se3 to become a reference material for the newly discovered three-dimensional topological insulators, which exhibit topologically protected conducting surface states that reside inside the bulk band gap. Studying topological insulators such as Bi2Se3 in nanostructures is advantageous because of the high surfaceto-volume ratio, which enhances effects from the surface states; recently reported Aharonov-Bohm oscillation in topological insulator nanoribbons by some of us is a good example. Theoretically, introducing magnetic impurities in topological insulators is predicted to open a small gap in the surface states by breaking time-reversal symmetry. Here, we present synthesis of magnetically doped Bi 2Se3 nanoribbons by vapor-liquid-solid growth using magnetic metal thin films as catalysts. Although the doping concentration is less than ∼2 %. low-temperature transport measurements of the Fe-doped Bi2Se3 nanoribbon devices show a clear Kondo effect at temperatures below 30 K, confirming the presence of magnetic impurities in the Bi2Se3 nanoribbons. The capability to dope topological insulator nanostructures magnetically opens up exciting opportunities for spintronics. © 2010 American Chemical Society.
Shahzad, Munir; Sengupta, Pinaki
2017-12-01
We investigate the necessary conditions for the emergence of complex, noncoplanar magnetic configurations in a Kondo lattice model with classical local moments on the geometrically frustrated Shastry-Sutherland lattice and their evolution in an external magnetic field. We demonstrate that topologically nontrivial spin textures, including a new canted flux state, with nonzero scalar chirality arise dynamically from realistic short-range interactions. Our results establish that a finite Dzyaloshinskii-Moriya (DM) interaction is necessary for the emergence of these novel magnetic states when the system is at half filling, for which the ground state is insulating. We identify the minimal set of DM vectors that are necessary for the stabilization of chiral magnetic phases. The noncoplanarity of such structures can be tuned continually by applying an external magnetic field. This is the first part in a series of two papers; in the following paper the effects of frustration, thermal fluctuations, and magnetic field on the emergence of novel noncollinear states at metallic filling of itinerant electrons are discussed. Our results are crucial in understanding the magnetic and electronic properties of the rare-earth tetraboride family of frustrated magnets with separate spin and charge degrees of freedom.
Energy Technology Data Exchange (ETDEWEB)
Schmidt, R.
2007-03-15
The present work is addressed to defects and boundaries in quantum field theory considering the application to AdS/CFT correspondence. We examine interactions of fermions with spins localised on these boundaries. Therefore, an algebra method is emphasised adding reflection and transmission terms to the canonical quantisation prescription. This method has already been applied to bosons in two space-time dimensions before. We show the possibilities of such reflection-transmission algebras in two, three, and four dimensions. We compare with models of solid state physics as well as with the conformal field theory approach to the Kondo effect. Furthermore, we discuss ansatzes of extensions to lattice structures. (orig.)
Pérez Daroca, Diego; Roura-Bas, Pablo; Aligia, Armando A.
2018-04-01
We study the low-temperature properties of the differential response of the current to a temperature gradient at finite voltage in a single-level quantum dot including electron-electron interaction, nonsymmetric couplings to the leads, and nonlinear effects. The calculated response is significantly enhanced in setups with large asymmetries between the tunnel couplings. In the investigated range of voltages and temperatures with corresponding energies up to several times the Kondo energy scale, the maximum response is enhanced nearly an order of magnitude with respect to symmetric coupling to the leads.
Energy Technology Data Exchange (ETDEWEB)
Buot, Felix A., E-mail: fbuot@gmu.edu [Computational Materials Science Center, George Mason University, Fairfax, VA 22030 (United States); TCSE Center, Spintronics Group, Physics Department, University of San Carlos, Talamban, Cebu 6000 (Philippines); C& LB Research Institute, Carmen, Cebu 6005 (Philippines); Otadoy, Roland E.S.; Rivero, Karla B. [TCSE Center, Spintronics Group, Physics Department, University of San Carlos, Talamban, Cebu 6000 (Philippines)
2017-03-01
Wide ranging interest in Dirac Hamiltonian is due to the emergence of novel materials, namely, graphene, topological insulators and superconductors, the newly-discovered Weyl semimetals, and still actively-sought after Majorana fermions in real materials. We give a brief review of the relativistic Dirac quantum mechanics and its impact in the developments of modern physics. The quantum band dynamics of Dirac Hamiltonian is crucial in resolving the giant diamagnetism of bismuth and Bi-Sb alloys. Quantitative agreement of the theory with the experiments on Bi-Sb alloys has been achieved, and physically meaningful contributions to the diamagnetism has been identified. We also treat relativistic Dirac fermion as an interband dynamics in uniform magnetic fields. For the interacting Bloch electrons, the role of translation symmetry for calculating the magnetic susceptibility avoids any approximation to second order in the field. The expressions for magnetic susceptibility of dilute nonmagnetic alloys give a firm theoretical foundation of the empirical formulas used in fitting experimental results. The unified treatment of all the above calculations is based on the lattice Weyl-Wigner formulation of discrete phase-space quantum mechanics. For completeness, the magnetic susceptibility of Kondo alloys is also given since Dirac fermions in conduction band and magnetic impurities exhibit Kondo effect.
Park, Wan Kyu; Sun, Lunan; Noddings, Alexander; Kim, Dae-Jeong; Fisk, Zachary; Greene, Laura H
2016-06-14
Samarium hexaboride (SmB6), a well-known Kondo insulator in which the insulating bulk arises from strong electron correlations, has recently attracted great attention owing to increasing evidence for its topological nature, thereby harboring protected surface states. However, corroborative spectroscopic evidence is still lacking, unlike in the weakly correlated counterparts, including Bi2Se3 Here, we report results from planar tunneling that unveil the detailed spectroscopic properties of SmB6 The tunneling conductance obtained on the (001) and (011) single crystal surfaces reveals linear density of states as expected for two and one Dirac cone(s), respectively. Quite remarkably, it is found that these topological states are not protected completely within the bulk hybridization gap. A phenomenological model of the tunneling process invoking interaction of the surface states with bulk excitations (spin excitons), as predicted by a recent theory, provides a consistent explanation for all of the observed features. Our spectroscopic study supports and explains the proposed picture of the incompletely protected surface states in this topological Kondo insulator SmB6.
Zhang, Jingdi; Yong, Jie; Takeuchi, Ichiro; Greene, Richard L.; Averitt, Richard D.
2018-04-01
We utilize terahertz time domain spectroscopy to investigate thin films of the heavy fermion compound Sm B6 , a prototype Kondo insulator. Temperature-dependent terahertz (THz) conductivity measurements reveal a rapid decrease in the Drude weight and carrier scattering rate at ˜T*=20 K , well below the hybridization gap onset temperature (100 K). Moreover, a low-temperature conductivity plateau (below 20 K) suggests the emergence of a surface state with an effective electron mass of 0.1 me . The conductivity dynamics following optical excitation is also measured and interpreted using Rothwarf-Taylor (R-T) phenomenology, yielding a hybridization gap energy of 17 meV. However, R-T modeling of the conductivity dynamics reveals a deviation from the expected thermally excited quasiparticle density at temperatures below 20 K, indicative of another channel opening up in the low-energy electrodynamics. Taken together, these results are consistent with the onset of a surface state well below the crossover temperature (100 K) after long-range coherence of the f -electron Kondo lattice is established.
Energy Technology Data Exchange (ETDEWEB)
Bingulac, B; Lazarevic, B; Matausek, M; Radanovic, Lj [Institut za nuklearne nauke Boris Kidric, Vinca, Beograd (Yugoslavia)
1964-07-01
A two-channel model for reactor dynamic analysis was developed. It enables representation of time dependent behaviour of a reactor as a whole and to obtain time and space dependent changes of temperature in any of the reactor channel. Model is suitable for follow-up of phenomena in limited time intervals up to few tens of minutes, since long term variations caused by fuel burnup and fission products are not taken into account in the model. Parameters are defined to cover the reactor power range from minimum to maximum. Model describes two main processes in the reactor: power generation dependent on the neutron flux and cooling.
Czech Academy of Sciences Publication Activity Database
Poltierová Vejpravová, Jana; Prokleška, J.; Pospíšil, J.; Kitazawa, H.; Goncalves, A.P.; Komatsubara, T.; Ritter, C.; Isnard, O.; Sechovský, V.
2012-01-01
Roč. 520, Apr (2012), s. 22-29 ISSN 0925-8388 Institutional research plan: CEZ:AV0Z10100520 Keywords : CePt 3 Ge * Kondo lattice * short-range magnetic order * size effect Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.390, year: 2012
Jean-Claude Gadmer
2013-01-01
09 September 2013 - Japanese Members of Internal Affairs and Communications Committee House of Representatives visiting the ATLAS experimental cavern with ATLAS Spokesperson D. Charlton. T. Kondo and K. Yoshida present.
Maximilien Brice
2007-01-01
Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) representative H. Ikukawa visiting ATLAS experiment with Collaboration Spokesperson P. Jenni, KEK representative T. Kondo and Advisor to CERN DG J. Ellis on 15 May 2007.
Shahzad, Munir; Sengupta, Pinaki
2017-08-01
We study the Shastry-Sutherland Kondo lattice model with additional Dzyaloshinskii-Moriya (DM) interactions, exploring the possible magnetic phases in its multi-dimensional parameter space. Treating the local moments as classical spins and using a variational ansatz, we identify the parameter ranges over which various common magnetic orderings are potentially stabilized. Our results reveal that the competing interactions result in a heightened susceptibility towards a wide range of spin configurations including longitudinal ferromagnetic and antiferromagnetic order, coplanar flux configurations and most interestingly, multiple non-coplanar configurations including a novel canted-flux state as the different Hamiltonian parameters like electron density, interaction strengths and degree of frustration are varied. The non-coplanar and non-collinear magnetic ordering of localized spins behave like emergent electromagnetic fields and drive unusual transport and electronic phenomena.
Energy Technology Data Exchange (ETDEWEB)
Maurya, A.; Thamizhavel, A.; Dhar, S.K. [Department of Condensed Matter Physics & Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005 (India); Provino, A.; Pani, M.; Costa, G.A. [Department of Chemistry, University of Genova, Via Dodecaneso 31, 16146 Genova (Italy); Institute SPIN-CNR, Corso Perrone 24, 16152 Genova (Italy)
2017-03-15
Single crystals of the new compound CeCu{sub 0.18}Al{sub 0.24}Si{sub 1.58} have been grown by high-temperature solution growth method using a eutectic Al-Si mixture as flux. This compound is derived from the binary CeSi{sub 2} (tetragonal α-ThSi{sub 2}-type, Pearson symbol tI12, space group I4{sub 1}/amd) obtained by partial substitution of Si by Cu and Al atoms but showing full occupation of the Si crystal site (8e). While CeSi{sub 2} is a well-known valence-fluctuating paramagnetic compound, the CeCu{sub 0.18}Al{sub 0.24}Si{sub 1.58} phase orders ferromagnetically at T{sub C}=9.3 K. At low temperatures the easy-axis of magnetization is along the a-axis, which re-orients itself along the c-axis above 30 K. The presence of hysteresis in the magnetization curve, negative temperature coefficient of resistivity at high temperatures, reduced jump in the heat capacity and a relatively lower entropy released up to the ordering temperature, and enhanced Sommerfeld coefficient (≈100 mJ/mol K{sup 2}) show that CeCu{sub 0.18}Al{sub 0.24}Si{sub 1.58} is a Kondo lattice ferromagnetic, moderate heavy fermion compound. Analysis of the high temperature heat capacity data in the paramagnetic region lets us infer that the crystal electric field split doublet levels are located at 178 and 357 K, respectively, and Kondo temperature (8.4 K) is of the order of T{sub C} in CeCu{sub 0.18}Al{sub 0.24}Si{sub 1.58}.
Heavy fermions and other highly correlated electron systems
International Nuclear Information System (INIS)
Schlottmann, P.
1991-01-01
In this paper I given a brief summary of the achievements grouped under three main headings, namely (1) heavy-fermion, mixed-valence and Kondo systems, (2) the n-channel Kondo problem and applications, and (3) one-dimensional conductors and antiferromagnets. The list of published papers and preprints is attached to the report, as well as a list of abstracts submitted to Conferences. All these papers are new in the sense that none of them was listed in the final technical report of grant DE-FG02-87ER45333
Mozaffari, Shirin; Guchhait, Samaresh; Markert, John T.
2017-10-01
We report the effects of oxygen pressure during growth (PO2 ) on the electronic and magnetic properties of PrAlO3 films grown on TiO2 -terminated SrTiO3 substrates. Resistivity measurements show an increase in the sheet resistance as PO2 is increased. The saturation of the sheet resistance down to 0.3 K is consistent with Kondo theory for PO2 ≥slant 10-5 torr. Resistivity data fits indicate Kondo temperatures of 16-18 K. For the 10-4 sample, we measured a moderate positive magnetoresistance (MR) due to a strong spin-orbit (SO) interaction at low magnetic fields that evolves into a larger negative MR at high fields due to the Kondo effect. Analysis of the MR data permitted the extraction of the SO interaction critical field for the PO2=10-5 torr interface ( H_SO=1.25 T). We observed high positive MR for the least oxygenated sample, where a fraction of the n-type carriers are derived from oxygen vacancies and possible cation interdiffusion; for this 6×10-6 torr sample, Hall effect data indicate a thick conducting layer. Its extremely high MR (˜400% ) is attributed to classical behavior due to a distribution of mobilities.
Directory of Open Access Journals (Sweden)
Andréa Bialetzki
1999-01-01
Full Text Available Analysis of drift of ichthyoplankton in two channels in the River Paraná, Brazil, were made. Sampling was undertaken from October 1995 to April 1996 during nychthemeral cycles. Water samples were collected to determine several environmental variables. Eggs densities largely differed to layers, times of day and months. In both the channels, highest occurrence of eggs was detected between January and March; greater concentrations at the bottom, during night. With regard to larvae, densities were significantly different in channels, times of days and months. Maximum occurrences were seen in the right channel, in both layers, with largest capture between January and March. Surface of the both channels presented highest density of larvae during night. Water temperature, electrical conductivity and flux velocity were different in the two channels, however, these variables and larvae density didn't showed correlations. This indicates that there was another possible factor, might be influencing the distribution of ichthyoplankton.Este trabalho teve por objetivo analisar a deriva do ictioplâncton em dois canais com diferentes condições de topografia e velocidade de fluxo, entre os estados do Paraná e Mato Grosso do Sul (Brasil. As amostragens foram realizadas no período de outubro de 1995 a abril de 1996, durante ciclos nictemerais. Amostras de água foram coletadas para determinação de algumas variáveis ambientais. A densidade de ovos diferiu significativamente entre os estratos, horários e meses; sendo que em ambos os canais, as maiores ocorrências de ovos foram verificadas entre janeiro e março, com maiores concentrações no fundo durante o período noturno. Com relação as larvas, as densidades diferiram entre os canais, horários e meses. As maiores ocorrências foram observas no canal direito, em ambos estratos, com maior período de captura entre janeiro e março. A superfície dos canais apresentou as maiores densidades de larvas
Quantum frustrated and correlated electron systems
Directory of Open Access Journals (Sweden)
P Thalmeier
2008-06-01
Full Text Available Quantum phases and fluctuations in correlated electron systems with frustration and competing interactions are reviewed. In the localized moment case the S=1/2 J1 - J2 - model on a square lattice exhibits a rich phase diagram with magnetic as well as exotic hidden order phases due to the interplay of frustration and quantum fluctuations. Their signature in magnetocaloric quantities and the high field magnetization are surveyed. The possible quantum phase transitions are discussed and applied to layered vanadium oxides. In itinerant electron systems frustration is an emergent property caused by electron correlations. It leads to enhanced spin fluctuations in a very large region of momentum space and therefore may cause heavy fermion type low temperature anomalies as in the 3d spinel compound LiV2O4 . Competing on-site and inter-site electronic interactions in Kondo compounds are responsible for the quantum phase transition between nonmagnetic Kondo singlet phase and magnetic phase such as observed in many 4f compounds. They may be described by Kondo lattice and simplified Kondo necklace type models. Their quantum phase transitions are investigated by numerical exact diagonalization and analytical bond operator methods respectively.
Song, Qi; Mi, Jian; Zhao, Dan; Su, Tang; Yuan, Wei; Xing, Wenyu; Chen, Yangyang; Wang, Tianyu; Wu, Tao; Chen, Xian Hui; Xie, X. C.; Zhang, Chi; Shi, Jing; Han, Wei
2016-01-01
There has been considerable interest in exploiting the spin degrees of freedom of electrons for potential information storage and computing technologies. Topological insulators (TIs), a class of quantum materials, have special gapless edge/surface states, where the spin polarization of the Dirac fermions is locked to the momentum direction. This spin–momentum locking property gives rise to very interesting spin-dependent physical phenomena such as the Edelstein and inverse Edelstein effects. However, the spin injection in pure surface states of TI is very challenging because of the coexistence of the highly conducting bulk states. Here, we experimentally demonstrate the spin injection and observe the inverse Edelstein effect in the surface states of a topological Kondo insulator, SmB6. At low temperatures when only surface carriers are present, a clear spin signal is observed. Furthermore, the magnetic field angle dependence of the spin signal is consistent with spin–momentum locking property of surface states of SmB6. PMID:27834378
Merker, L.; Kirchner, S.; Muñoz, E.; Costi, T. A.
2014-08-01
The Comment of A. A. Aligia claims that the superperturbation theory (SPT) approach [E. Muñoz, C. J. Bolech, and S. Kirchner, Phys. Rev. Lett. 110, 016601 (2013), 10.1103/PhysRevLett.110.016601] formulated using dual fermions [A. N. Rubtsov, M. I. Katsnelson, and A. I. Lichtenstein, Phys. Rev. B 77, 033101 (2008), 10.1103/PhysRevB.77.033101] and used by us to compare with numerical renormalization group (NRG) results for the conductance [L. Merker, S. Kirchner, E. Muñoz, and T. A. Costi, Phys. Rev. B 87, 165132 (2013), 10.1103/PhysRevB.87.165132], fails to correctly extend the results of the symmetric Anderson impurity model (SIAM) for general values of the local level Ed in the Kondo regime. We answer this criticism. We also compare new NRG results for cB, with cB calculated directly from the low-field conductance, with new higher-order SPT calculations for this quantity, finding excellent agreement for all Ed and for U /πΔ extending into the strong coupling regime.
Jang, Kuk-In; Shim, Miseon; Lee, Sang Min; Huh, Hyu Jung; Huh, Seung; Joo, Ji-Young; Lee, Seung-Hwan; Chae, Jeong-Ho
2017-11-01
The Sewol ferry capsizing accident on South Korea's southern coast resulted in the death of 304 people, and serious bereavement problems for their families. Electroencephalography (EEG) beta frequency is associated with psychiatric symptoms, such as insomnia. The aim of this study was to investigate the relation between frontal beta power, psychological symptoms, and insomnia in the bereaved families. Eighty-four family members of the Sewol ferry victims (32 men and 52 women) were recruited and their EEG was compared with that of 25 (13 men and 12 women) healthy controls. A two-channel EEG device was used to measure cortical activity in the frontal lobe. Symptom severity of insomnia, post-traumatic stress disorder, complicated grief, and anxiety were evaluated. The bereaved families showed a higher frontal beta power than healthy controls. Subgroup analysis showed that frontal beta power was lower in the individuals with severe insomnia than in those with normal sleep. There was a significant inverse correlation between frontal beta power and insomnia symptom in the bereaved families. This study suggests that increased beta power, reflecting the psychopathology in the bereaved families of the Sewol ferry disaster, may be a compensatory mechanism that follows complex trauma. Frontal beta power could be a potential marker indicating the severity of sleep disturbances. Our results suggest that sleep disturbance is an important symptom in family members of the Sewol ferry disaster's victims, which may be screened by EEG beta power. © 2017 The Authors. Psychiatry and Clinical Neurosciences © 2017 Japanese Society of Psychiatry and Neurology.
Non-Fermi liquid and spin-glass behavior of the Sc1-xUxPd3 system
International Nuclear Information System (INIS)
Gajewski, D.A.; Allenspach, P.; Seaman, C.L.; Maple, M.B.
1994-01-01
Previous electrical resistivity ρ(T), magnetic susceptibility χ(T), and specific heat C(T) measurements on the Y 1-x U x Pd 3 system have revealed Kondo behavior for 0 K , where T K is the Kondo temperature: ρ(T)/ρ(0)∼1-T/(aT K ) and C(T)/T∼-(1/T K )ln T with evidence for a finite T=0 residual entropy S(0)=(R/2)ln(2). We report measurements of ρ(T), χ(T), and C(T) on the Sc 1-x U x Pd 3 system which reveal similar Kondo, non-Fermi liquid, and spin-glass behaviors. ((orig.))
Effects of Luttinger leads on the AC conductance of a quantum dot
Energy Technology Data Exchange (ETDEWEB)
Yang, Kai-Hua, E-mail: khy@bjut.edu.cn [College of Applied Sciences, Beijing University of Technology, Beijing 100122 (China); Qin, Chang-Dong [College of Applied Sciences, Beijing University of Technology, Beijing 100122 (China); Wang, Huai-Yu [Department of Physics, Tsinghua University, Beijing 100084 (China); Liu, Kai-Di [College of Applied Sciences, Beijing University of Technology, Beijing 100122 (China)
2017-04-18
Highlights: • The system exhibits photon-assisted single- and two-channel Kondo physics, depending on the intralead interaction. • The 1CK and 2CK mechanisms can coexist within a region of the intralead interaction parameter. • In the limit of strong interaction, the differential conductance scales as a power law both in bias voltage and in temperature. - Abstract: We investigate the joint effects of the intralead electron interaction and an external alternating gate voltage on the transport of a quantum dot coupled to two Luttinger liquid leads in the Kondo regime. We find the transferring between two Kondo physics mechanics by investigation of differential conductance. For very weak intralead interaction, the satellite and main Kondo resonant peaks appear in the differential conductance. For moderately strong intralead interaction, all the peaks disappear and evolve into dips, which signifies that a photon-assisted single-channel Kondo (1CK) physics turns into two-channel Kondo (2CK) physics. The 1CK and 2CK mechanisms can coexist within a region of the intralead interaction parameter. The 1CK physics transits to the 2CK one gradually, not suddenly. In the limit of strong interaction, all dips disappear. When the bias voltage is small, there is no photon exchange between the quantum dot and alternative field, and the differential conductance scales as a power law both in bias voltage and in temperature. As the field becomes stronger, the quantum dot will emit and absorb photons.
TRANSPORT PROPERTIES OF THE STRONGLY CORRELATED SYSTEMS
Directory of Open Access Journals (Sweden)
T.Domanski
2004-01-01
Full Text Available The transport properties of various systems are studied here in the context of three different models. These are: - the disordered Hubbard model applicable to correlated binary alloys with a general disorder, - the Anderson model used in describing the Kondo physics of a quantum dot connected to the external superconducting leads, and - the Ranninger-Robaszkiewicz model applied to the study of optical properties of the system with preformed electron pairs above the temperature of transition to the superconducting state. We calculate the density of states, specific heat, the Wilson ratio and conductivity of the correlated binary alloy with off-diagonal disorder. We investigate the conditions under which the Kondo peak appears in the density of states and in the conductance of a dot coupled to the external superconducting leads. We analyze the effect of the pseudogap on the optical spectra in the high temperature superconductors described by the boson-fermion model.
Pressure effects on the magnetic and transport properties of the Kondo lattice system Ce3RuSn6
Wakiya, Kazuhei; Tomaki, Takeru; Kimura, Minami; Uehara, Masatomo; Gouchi, Jun; Uwatoko, Yoshiya; Umehara, Izuru
2018-05-01
The magnetization and electrical resistivity of Ce3RuSn6 have been measured in the temperature range from 2 to 300 K and in the pressure range up to 1 GPa. At ambient pressure, the magnetization shows a ferromagnetic-like steep rise below 4 K. The electrical resistivity drops at TC = 3.3 K due to the magnetic transition. We found that TC is slightly enhanced by applying pressure, suggesting that this compound sits on the left side of the peak in the Doniach phase diagram.
Magneto-heat capacity study on Kondo lattice system Ce(Ni1−xCux ...
Indian Academy of Sciences (India)
Author for correspondence (vganesan@csr.res.in) also been speculated from the resistivity under magnetic fields that the formation of a Fermi liquid-like behaviour is quite probable and is in line with the expectations of specific heat studies [17]. However, a convincing study is needed towards this and is the aim of the ...
International Nuclear Information System (INIS)
Shimada, K.; Higashiguchi, M.; Fujimori, S.-I.; Saitoh, Y.; Fujimori, A.; Namatame, H.; Taniguchi, M.; Sasakawa, T.; Takabatake, T.
2006-01-01
High-resolution resonance-photoemission spectroscopy has been performed on the Ce 1- x La x RhAs (0≤x≤0.05) single crystal to elucidate a collapse of the energy gap in the Kondo semiconductor CeRhAs by La substitution. With increasing x, the spectral intensity of the Ce4f 1 derived states near the Fermi level decreases and new 4f derived spectral feature appears at a higher binding energy. The Rh4d-derived states, on the other hand, are not significantly changed by the substitution. New 4f-derived states have incoherent nature, which is responsible for the collapse of the semiconducting state for x>∼0.02
[Mixed valent and heavy ferimons and related systems
International Nuclear Information System (INIS)
Schlottmann, P.
1991-01-01
The main objective of the project is to gain a better understanding of highly correlated fermion systems. High correlations appear in a variety of solid state phenomena: mixed-valence and heavy-fermions or Kondo systems, superfluid and normal He 3 , high-temperature superconductors, magnetism in low dimensions, quantum Hall effect, spin-fluctuations in transition metals, giant magnetic moments, tunneling of an atom interacting with a degenerate electron gas, quantum dissipative systems, organic superconductors, etc. The primary focus of the work is on valence mixing and heavy fermions, but elated highly correlated systems are also studied. In this paper a brief summary of the achievements grouped under four headings, namely (1) heavy fermions-mixed valence-Kondo, (2) magnetism in low dimensions, (3) narrow band phenomena/Hubbard model and (4) collaborations with experimentalists
Torre, L D L; Ellerby, M; McEwen, K A
2003-01-01
We report on electrical resistivity measurements performed on polycrystalline samples of UCu sub 5 sub - sub x Ni sub x (x = 0.25, 1). In order to extract the Kondo contribution to the resistivity, the experiments were carried out over a wide temperature range (0.4-800 K). From the analysis of our results, we conclude that the Kondo temperature takes values of T sub K approx 240 K for x = 1 and T sub K approx 245 K for x = 0.25, and that for both Ni concentrations the dominant part of the remarkably high residual resistivity (rho(0) approx 400 mu OMEGA cm) corresponds to the Kondo contribution. These results are discussed in comparison with previous analysis of specific heat and magnetic susceptibility data that produced similar values of T sub K. We interpret our results in terms of disorder-driven non-Fermi liquid behaviour for UCu sub 4 Ni, as indicated by the anomalous temperature dependences of the electrical, thermal and magnetic properties previously observed in this compound.
RKKY interaction in mixed valence system and heavy fermion superconductivity
International Nuclear Information System (INIS)
Fusui Liu; Gao Lin; Lin Zonghan
1985-11-01
The 1-D RKKY interaction of mixed valence system is given by using the thermodynamic perturbation theory. The numerical comparisons of 1-D and 3-D RKKY interaction between systems with localized magnetic moments of mixed valence and non-mixed valence show that the former is much stronger than the latter. From some analyses we propose that the heavy Fermion superconductivity comes from the RKKY interaction between two local f electrons which hop off the impurity site to become two continuum electrons. The source of the two impurity electrons hopping is the Coulomb interaction. It is also emphasized that the RKKY interaction does not disappear for the Kondo lattice, when the temperature is less than the Kondo temperature. (author)
Magnetic properties of Ce{sup 3+} in Pb{sub 1{minus}x}Ce{sub x}Se: Kondo and crystal-field effect
Energy Technology Data Exchange (ETDEWEB)
Gratens, X.; Charar, S.; Averous, M. [Groupe dEtude des Semiconducteurs URA 357, Universite Montpellier II, Place Eugene Bataillon, 34095 Montpellier Cedex 5 (France); Isber, S. [Department of Physic, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, Quebec, H3G 1M8 (CANADA); Deportes, J. [Laboratoire Louis Neel, Avenue des Martyres, BP 166X, 38042 Grenoble Cedex 9 (France); Golacki, Z. [Institute of Physics, Polish Academy of Sciences, Pl. 02-668, Warsaw (Poland)
1997-10-01
Electron paramagnetic resonance (EPR) experiments were performed on a Pb{sub 1{minus}x}Ce{sub x}Se crystal at liquid-helium temperatures and show very clearly that the doublet {Gamma}{sub 7} is the ground state for cerium ions. The cubic symmetry is shown and the effective Land{acute e} factor for the Ce{sup 3+} is determined to be 1.354{plus_minus}0.003. An orbital reduction factor is introduced to explain the g experimental value. High-field magnetization results are in good agreement with the EPR results. The nominal Ce composition in PbSe deduced from saturation of the magnetization, x=0.0405{plus_minus}0.0003, is very closed to the value determined by microprobe analysis (x=0.04). At 1.5 K, an antiferromagnetic interaction between the nearest-neighbor cerium atoms is found, J{sub ex}/k{sub B}={minus}0.715thinspK. The low-field magnetic-susceptibility results show that the magnetic moment of cerium impurities is strongly temperature dependent, explained by the presence of the crystal-field effect and the Kondo effect. {copyright} {ital 1997} {ital The American Physical Society}
Matsumura, M; Takabatake, T; Tsuji, S; Tou, H; Sera, M
2003-01-01
sup 7 sup 5 As NQR/NMR studies were performed to investigate the successive phase transitions found recently, the gap formation and their interplay in a Kondo semiconductor CeRhAs. NQR/NMR spectra in their respective phases change, reflecting lattice modulation modes, q sub 1 = (0, 1/2, 1/2), q sub 2 = (0, 1/3, 1/3) and q sub 3 = (1/3, 0, 0). In particular for well-resolved three NQR lines corresponding to the q sub 3 mode in the lowest temperature phase, the nuclear spin-lattice relaxation rate (T sub 1 T) sup - sup 1 shows an activation type T-dependence, suggesting a gap opening over the entire Fermi surface, in contrast to the V-shaped gap in isostructural CeNiSn and CeRhSn. The evaluated gap of 272 K and the bandwidth of about 4000 K are one order of magnitude larger than those in CeNiSn and CeRhSb. A lattice modulation forms a gap different from the V-shaped gap. (author)
Effect of c-f hybridization on electric and magnetic properties of some Heavy Fermion (HF) systems
Energy Technology Data Exchange (ETDEWEB)
Sahoo, J., E-mail: jitendrasahoo2008@gmail.com [Regional Office of Vocational Education, Sambalpur, Odisha -768 004 (India); Nayak, P. [School of Physics, Sambalpur University, Sambalpur, Odisha - 768 019 (India)
2017-02-01
Representing the heavy fermion systems by the Periodic Anderson Model (PAM), we have used Zubarev technique to see the effect of c-f hybridization on the temperature dependence of resistivity and magnetic susceptibility. The calculated resistivity and magnetic susceptibility show the general features observed in these materials experimentally. Further, we have shown how the strength of hybridization as well as the position of the f-level affects both the properties and the Kondo temperature of these systems.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Lei; Schackert, Michael; Miyamachi, Toshio; Yamada, Toyokazu; Wulfhekel, Wulf [Physikalisches Institut, Karlsruhe Institut of Technology (Germany); Schramm, Frank; Ruben, Mario [Institut of Nanotechnology, Karlsruhe Institut of Technology (Germany)
2011-07-01
Single molecular magnets (SMM) attract much interest due to their potential applications in spintronics. We investigated metal organic molecules based on (hfaa){sub 4}(bpm) containing two 3d ions (Ni or Mn) using low temperature scanning tunneling microscopy (STM) at 1 K in ultra-high vacuum. In the bulk, the two metallic ions couple antiferromagnetically leading to an S=0 ground state. The Ni{sub 2} and Mn{sub 2} molecules were sublimed onto atomically clean Cu(100) surfaces resulting in two different absorptions configurations. Scanning tunneling spectroscopy (STS) with a high energy resolution of 0.3 meV showed a strong Kondo resonance on the position of the metal ions inside the molecules indicating that the hybridization of the local spins with the substrate is more efficient than their antiferromagnetic coupling. The Fano resonance showed a pronounced dependence on the adsorption geometry indicating different Kondo temperatures and q-parameters. This is explained by a adsorption dependent hybridization between SMM and the substrate.
Raphaël Piguet
2011-01-01
31st August 2011 - Government of Japan R. Chubachi, Executive Member of the Council for Science and Technology Policy, Cabinet Office, Vice Chairman, Representative Corporate Executive Officer and Member of the Board, Sony Corporation, visiting the ATLAS experimental area with Former Collaboration Spokesperson P. Jenni and Senior physicist T. Kondo.
Maximilien Brice
2010-01-01
2nd September 2010 - Japanese Senior Vice-Minister of the Environment I. Tajima signing the guest book with Director-General R. Heuer and visiting the ATLAS control room with physicists T. Kondo and H. Fukuda, Members of the ATLAS Collaboration and KEK.
Jean-Claude Gadmer
2013-01-01
30 August 2013 - Senior Vice Minister for Foreign Affairs in Japan M. Matsuyama signing the guest book with CERN Director-General; visit the ATLAS experimental cavern with ATLAS Spokesperson D. Charlton and visiting the LHC tunnel at Point 1 with former ATLAS Japan national contact physicist T. Kondo. R. Voss and K. Yoshida present throughout.
2011-01-01
19 September 2011 - Japan Science and Technology Agency President K. Kitazawa visiting the LHC superconducting magnet test hall with engineer M. Bajko; the ATLAS visitor centre with Collaboration Former Spokesperson P. Jenni and Senior Scientist T. Kondo; signing the guest book with Adviser R.Voss and Head of International Relations F. Pauss.
Influence of spin correlations in the transport properties of a double quantum dot system
Costa Ribeiro, Laercio; Hamad, Ignacio; Chiappe, Guillermo; Victoriano Anda, Enrique
2013-03-01
In this work we study the influence of spin correlations in the transport properties of a system consisting of two quantum dots (QDs) with high Coulomb interaction U which are interconnected through a chain of N non-interacting sites and individually coupled to two metallic leads. Using both the finite U slave boson mean field approach (FUSBMFA) and the Logarithmic-discretization-embedded-cluster approximation (LDECA) we studied the system in different regions of the parameter space for which we calculate many physical quantities, namely local density of states, conductance, total spin, spin correlations, in addition to the renormalization parameters associated with the FUSBMFA. The results reveled a very rich physical scenario which is manifested by at least two different Kondo regimes, the well-known spin s = 1/2 and some other type of Kondo effect which appears as a result of the coupling between the QDs and the non-interacting central sites. We also consider the possibility of accessing some kind of Kondo box effect due to the discrete nature of the central chain and study how this regime is affected by the magnetic interaction between the local spins of the QD's and by the interaction between these spins and the spins of the conduction electros in the leads.
International Nuclear Information System (INIS)
Hintersteiner, Martin; Auer, Manfred
2013-01-01
One-bead one-compound combinatorial library beads exhibit varying levels of autofluorescence after solid phase combinatorial synthesis. Very often this causes significant problems for automated on-bead screening using TentaGel beads and fluorescently labeled target proteins. Herein, we present a method to overcome this limitation when fluorescence activated bead sorting is used as the screening method. We have equipped the COPAS bead sorting instrument with a high-speed profiling unit and developed a spectral autofluorescence correction method. The correction method is based on a simple algebraic operation using the fluorescence data from two detection channels and is applied on-the-fly in order to reliably identify hit beads by COPAS bead sorting. Our method provides a practical tool for the fast and efficient isolation of hit beads from one-bead one-compound library screens using either fluorescently labeled target proteins or biotinylated target proteins. This method makes hit bead identification easier and more reliable. It reduces false positives and eliminates the need for time-consuming pre-sorting of library beads in order to remove autofluorescent beads. (technical note)
De Franceschi, Silvano; van der Wiel, Wilfred Gerard; Sattler, Klaus D.
The research community has long understood the value of formal specifications in building robust software. However, the adoption of any specifications beyond run-time assertions in industrial software has been limited. All of this has changed at Microsoft in the last few years. Today, formal
Studies of heavy fermion systems: Progress report, July 1, 1986-December 31, 1987
International Nuclear Information System (INIS)
Stewart, G.R.
1987-08-01
Studies of the resistivity, susceptibility, and specific heat of the new heavy fermion system UPt/sub 5-x/Au/sub x/ have shown: (1) the high effective mass, m*, can be varied by almost an order of magnitude by varying x near x = 1; and (2) the occurrence of high m* in this system and (presumably) in heavy fermion systems in general is typified by a nearness to magnetic instability. High field (24 T) specific heat studies of CeCu 6 show a total suppression of the low temperature heavy fermion ground state by magnetic field, in direct contradiction of present non-interacting ''Kondo lattice'' theory
Energy Technology Data Exchange (ETDEWEB)
Togo, K [Yomiuri Koto Institute of Science and Engineering, Tokyo (Japan); Kondo, M [Tokyo Institute of Technology, Tokyo (Japan)
1997-10-01
One of the authors intended before to understand the fundamentals of automobile steering emphasizing the importance of the driver`s forward view point. This idea was called Kondo`s hypothesis by several Professors and has been used and developed by many researchers in Japan. Using this thought, dynamical properties and steering of four-wheel steering vehicles, of which two points of the vehicle`s body can trace the designated course, are studied in this paper. Some numerical calculations have shown the tendency similar to the actual steering now used by a Japanese manufacturer. This idea would be useful in the automatic driving systems such as ITS. 4 refs., 3 tabs., 1 tab.
Low-energy physics of high-temperature superconductors
International Nuclear Information System (INIS)
Emery, V.J.; Kivelson, S.A.
1992-01-01
It is argued that the low-energy properties of high temperature superconductors are dominated by the interaction between the mobile holes and a particular class of collective modes, corresponding to local large-amplitude low-energy fluctuations in the hole density. The latter are a consequence of the competition between the effects of long-range Coulomb interactions and the tendency of a low concentration of holes in an antiferromagnet to phase separate. The low-energy behavior of the system is governed by the same fixed point as the two-channel Kondo problem, which accounts for the ''universality'' of the properties of the cuprate superconductors. Predictions of the optical properties and the spin dynamics are compared with experiment. The pairing resonance of the two Kondo problem gives a mechanism of high temperature superconductivity with an unconventional symmetry of the order parameter
VIBRO-DIAGNOSTIC SYSTEM ON BASIS OF PERSONAL COMPUTER
Directory of Open Access Journals (Sweden)
V. V. Bokut
2007-01-01
Full Text Available A system for vibration diagnostics based on a mobile computer and two-channel microprocessor measuring device has been developed. Usage of fast Hartley-Fourier transform allows to increase frequency resolution up to 25000 spectral lines that makes it possible to use the system for wide range of applications.
Coaxial two-channel high-gradient dielectric wakefield accelerator
Directory of Open Access Journals (Sweden)
G. V. Sotnikov
2009-06-01
Full Text Available A new scheme for a dielectric wakefield accelerator is proposed that employs a cylindrical multizone dielectric structure configured as two concentric dielectric tubes with outer and inner vacuum channels for drive and accelerated bunches. Analytical and numerical studies have been carried out for such coaxial dielectric-loaded structures (CDS for high-gradient acceleration. An analytical theory of wakefield excitation by particle bunches in a multizone CDS has been formulated. Numerical calculations are presented for an example of a CDS using dielectric tubes with dielectric permittivity 5.7, having external diameters of 2.121 and 0.179 mm with inner diameters of 2.095 and 0.1 mm. An annular 5 GeV, 6 nC electron bunch with rms length of 0.035 mm energizes a wakefield on the structure axis having an accelerating gradient of ∼600 MeV/m with a transformer ratio ∼8∶1. The period of the accelerating field is ∼0.33 mm. If the width of the drive bunch channel is decreased, it is possible to obtain an accelerating gradient of >1 GeV/m while keeping the transformer ratio approximately the same. Full numerical simulations using a particle-in-cell code have confirmed results of the linear theory and furthermore have shown the important influence of the quenching wave that restricts the region of the wakefield to within several periods following the drive bunch. Numerical simulations for another example have shown nearly stable transport of drive and accelerated bunches through the CDS, using a short train of drive bunches.
TWO CHANNELS OF SELF-ORGANIZATION OF IONIZED GASEOUS MEDIA
Directory of Open Access Journals (Sweden)
Benedict Oprescu
2013-12-01
Full Text Available The appearance is pointed out, experimentally, of a complex electric charge structure, within an ionized gas, relatively homogeneous at first, under the influence of a number of external constraints. Two different mechanisms of self-organization are presented: the former implying, essentially, long-range interactions, and the latter implying, essentially, short-range quantum interactions. The phenomenological scenarios are presented, which underlie the two mechanisms of self-organization, as well as the broader theoretical frame, currently accepted, concerning the generation of complexity in the material media that are far from the state of thermodynamic equilibrium.
Transfer of spectral weight in spectroscopies of correlated electron systems
International Nuclear Information System (INIS)
Rozenberg, M.J.; Kotliar, G.; Kajueter, H.
1996-01-01
We study the transfer of spectral weight in the photoemission and optical spectra of strongly correlated electron systems. Within the local impurity self-consistent approximation, that becomes exact in the limit of large lattice coordination, we consider and compare two models of correlated electrons, the Hubbard model and the periodic Anderson model. The results are discussed in regard to recent experiments. In the Hubbard model, we predict an anomalous enhancement optical spectral weight as a function of temperature in the correlated metallic state which is in qualitative agreement with optical measurements in V 2 O 3 . We argue that anomalies observed in the spectroscopy of the metal are connected to the proximity to a crossover region in the phase diagram of the model. In the insulating phase, we obtain excellent agreement with the experimental data, and present a detailed discussion on the role of magnetic frustration by studying the k-resolved single-particle spectra. The results for the periodic Anderson model are discussed in connection to recent experimental data of the Kondo insulators Ce 3 Bi 4 Pt 3 and FeSi. The model can successfully explain the thermal filling of the optical gap and the corresponding changes in the photoemission density of states. The temperature dependence of the optical sum rule is obtained, and its relevance to the interpretation of the experimental data discussed. Finally, we argue that the large scattering rate measured in Kondo insulators cannot be described by the periodic Anderson model. copyright 1996 The American Physical Society
International Nuclear Information System (INIS)
Cox, D.L.
1995-01-01
This is a progress report for the DOE project covering the period 2/15/94 to 2/14/95. The PI had a fruitful sabbatical during this period, and had some important new results, particularly in the area of new phenomenology for heavy fermion superconductivity. Significant new research accomplishments are in the area of odd-in-time-reversal pairing states/staggered superconductivity, the two-channel Kondo lattice, and a general model for Ce impurities which admits one-, two-, and three-channel Kondo effects. Papers submitted touch on these areas: staggered superconductivity - a new phenomenology for UPt 3 ; theory of the two-channel Kondo lattice in infinite dimensions; general model of a Ce 3+ impurity. Other work was done in the areas: Knight shift in heavy fermion alloys and compounds; symmetry analysis of singular pairing correlations for the two-channel Kondo impurity model
IMPECC, new 4 π β γ coincidence system
International Nuclear Information System (INIS)
Bouchard, J.; Chauvenet, B.; Vatin, R.
1988-05-01
The new 4 π β γ coincidence system IMPECC which uses an extensible dead time circuit common to both channels is described. Correction formulae which take into account the particularities of the electronics are also presented. The use of two ADC's and the symmetry in the two channels gives us a very powerful instrument when measuring complex decay scheme radionuclides [fr
Energy Technology Data Exchange (ETDEWEB)
Dhar, S. K., E-mail: sudesh@tifr.res.in [DCMPMS, T.I.F.R., Homi Bhabha Road, Colaba, Mumbai 400005 (India); Aoki, Y.; Suemitsu, B.; Miyazaki, R. [Department of Physics, Tokyo Metropolitan University, Minami-Ohsawa 1-1, Hachioji-Shi, Tokyo (Japan); Provino, A.; Manfrinetti, P. [Departimento Physica Chemicale, Universita di Genova, Via Dodecaneso, 16146 Genova (Italy)
2014-05-07
We have probed the effect of doping CePtZn with Au and Ni and also investigated in detail the magnetic behavior of the iso-structural CeAuZn. A magnetic ground state is observed in both CePt{sub 0.9}Au{sub 0.1}Zn and CePt{sub 0.9}Ni{sub 0.1}Zn with T{sub N} = 2.1 and 1.1 K and the coefficient of the linear term of electronic heat capacity γ = 0.34 and 0.9 J/mol K{sup 2}, respectively. The corresponding values for CePtZn are 1.7 K and 0.6 J/mol K{sup 2}. The altered values of T{sub N} and γ show that the electronic correlations in CePtZn are affected by doping with Au and Ni. CeAuZn orders magnetically near 1.7 K and its electrical resistivity shows a normal metallic behavior. Together with a γ of 0.022 J/mol K{sup 2} the data indicate a weak 4f-conduction electron hybridization in CeAuZn characteristic of normal trivalent cerium based systems.
Physics of zero- and one-dimensional nanoscopic systems
Maiti, Santanu; Chowdhury, Jayeeta
2007-01-01
In recent years submicron and nanoscale systems have featured strongly on the research agenda due to the technological progress and new physics that have emerged from studies of ultra-small systems. A fundamental understanding of basic physical phenomena on the mesoscopic and nanoscopic scales is required to exploit the technological potential offered by these exotic materials. The present book contains review-like chapters by some of the leading experts in the field, covering topics such as the Kondo effect, electron transport, disorder and quantum coherence with electron-electron interaction, persistent current, thermoelectric phenomena, etc. in quantum dots, quantum wires, carbon nanotubes and more. This book will be valuable to researchers and students in condensed matter physics.
Study of spin-polaron formation in 1D systems
Energy Technology Data Exchange (ETDEWEB)
Arredondo, Y.; Navarro, O. [Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, 04510 México D.F. (Mexico); Vallejo, E. [Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Coahuila, Carretera Torreón-Matamoros Km. 7.5 Ciudad Universitaria, 27276 Torreón, Coahuila (Mexico)
2014-05-15
We study numerically the formation of spin-polarons in low-dimensional systems. We consider a ferromagnetic Kondo lattice model with Hund coupling J{sub H} and localized spins interacting antiferromagnetically with coupling constant J. We investigate the ground state phase diagram as a function of the exchange couplings J{sub H} and J and as a function of the band filling, since it has been observed that doping either on the ferromagnetic or antiferromagnetic regime lead to formation of magnetic domains [1]. We explore the quasi-particle formation and phase separation using the density-matrix renormalization group method, which is a highly efficient method to investigate quasi-one-dimensional strongly correlated systems.
Study of spin-polaron formation in 1D systems
International Nuclear Information System (INIS)
Arredondo, Y.; Navarro, O.; Vallejo, E.
2014-01-01
We study numerically the formation of spin-polarons in low-dimensional systems. We consider a ferromagnetic Kondo lattice model with Hund coupling J H and localized spins interacting antiferromagnetically with coupling constant J. We investigate the ground state phase diagram as a function of the exchange couplings J H and J and as a function of the band filling, since it has been observed that doping either on the ferromagnetic or antiferromagnetic regime lead to formation of magnetic domains [1]. We explore the quasi-particle formation and phase separation using the density-matrix renormalization group method, which is a highly efficient method to investigate quasi-one-dimensional strongly correlated systems
Bound states in strongly correlated magnetic and electronic systems
International Nuclear Information System (INIS)
Trebst, S.
2002-02-01
A novel strong coupling expansion method to calculate two-particle spectra of quantum lattice models is developed. The technique can be used to study bosonic and fermionic models and in principle it can be applied to systems in any dimension. A number of strongly correlated magnetic and electronic systems are examined including the two-leg spin-half Heisenberg ladder, the dimerized Heisenberg chain with a frustrating next-nearest neighbor interaction, coupled Heisenberg ladders, and the one-dimensional Kondo lattice model. In the various models distinct bound states are found below the two-particle continuum. Quantitative calculations of the dispersion, coherence length and binding energy of these bound states are used to describe spectroscopic experiments on (Ca,La) 14 Cu 24 O 41 and NaV 2 O 5 . (orig.)
Ground state of the parallel double quantum dot system.
Zitko, Rok; Mravlje, Jernej; Haule, Kristjan
2012-02-10
We resolve the controversy regarding the ground state of the parallel double quantum dot system near half filling. The numerical renormalization group predicts an underscreened Kondo state with residual spin-1/2 magnetic moment, ln2 residual impurity entropy, and unitary conductance, while the Bethe ansatz solution predicts a fully screened impurity, regular Fermi-liquid ground state, and zero conductance. We calculate the impurity entropy of the system as a function of the temperature using the hybridization-expansion continuous-time quantum Monte Carlo technique, which is a numerically exact stochastic method, and find excellent agreement with the numerical renormalization group results. We show that the origin of the unconventional behavior in this model is the odd-symmetry "dark state" on the dots.
Energy Technology Data Exchange (ETDEWEB)
Santos, C.A.M. dos
2005-06-24
This thesis focuses on the theoretical investigation of the temperature dependent electronic and magnetic properties of metallic 4f-systems with localized magnetic moments. The presented theory is based on the Kondo-lattice model, which describes the interaction between a system of 4f-localized magnetic moments and the itinerant conduction band electrons. This interaction is responsible for a remarkable temperature dependence of the electronic structure mainly induced by the subsystem of 4f-localized moments. The many-body problem provoked by the Kondo-lattice model is solved by using a moment conserving Green function technique, which takes care of several special limiting cases. This method reproduces the T=0-exact solvable limiting case of the ferromagnetically saturated semiconductor. The temperature dependent magnetic properties of the 4f-localized subsystem are evaluated by means of a modified Rudermann-Kittel-Kasuya-Yosida (RKKY) type procedure, which together with the solution of the electronic part allows for a self-consistent calculation of all the electronic and magnetic properties of the model. Results of model calculations allow to deduce the conditions for ferromagnetism in dependence of the electron density n, exchange coupling J and temperature T. The self-consistently calculated Curie temperature T{sub C} is presented and discussed in dependence of relevant parameters (J, n, and W) of the model. The second part of the thesis is concerned with the investigation of the temperature dependence of the electronic and magnetic properties of the rare-earth metal Gadolinium (Gd). The original Kondo-lattice model is extended to a multi-band Kondo-lattice model and combined with an ab-initio band structure calculation to take into account for the multi-bands in real systems. The single-particle energies of the model are taken from an augmented spherical wave (ASW) band structure calculation. The proposed method avoids the double counting of relevant
Theory of Kondo effect in superconductors, 2
International Nuclear Information System (INIS)
Ichinose, Shin-ichi
1977-01-01
Thermodynamic properties of superconducting alloys near the transition temperature are studied within the interpolation approximation which is constructed so as to coincide with theories in limiting cases. By the use of this approximation, the specific heat jump at the transition temperature is calculated in the case of the magnitude of the impurity spin being 1/2. The result shows a continuous change of the specific heat jump with T sub(K)/T sub(c0) from the Abrikosov-Gorkov value to essentially BCS-like behavior in contrast to the Mueller-Hartmann-Zittartz theory. One has an example of a cross over between a weak coupling situation at T sub(K)/T sub(c0) > 1. The Hartree-Fock theory is also discussed in connection with the present calculation. (auth.)
Dynamics of symmetry breaking during quantum real-time evolution in a minimal model system.
Heyl, Markus; Vojta, Matthias
2014-10-31
One necessary criterion for the thermalization of a nonequilibrium quantum many-particle system is ergodicity. It is, however, not sufficient in cases where the asymptotic long-time state lies in a symmetry-broken phase but the initial state of nonequilibrium time evolution is fully symmetric with respect to this symmetry. In equilibrium, one particular symmetry-broken state is chosen as a result of an infinitesimal symmetry-breaking perturbation. From a dynamical point of view the question is: Can such an infinitesimal perturbation be sufficient for the system to establish a nonvanishing order during quantum real-time evolution? We study this question analytically for a minimal model system that can be associated with symmetry breaking, the ferromagnetic Kondo model. We show that after a quantum quench from a completely symmetric state the system is able to break its symmetry dynamically and discuss how these features can be observed experimentally.
Transport through correlated systems with density functional theory.
Kurth, S; Stefanucci, G
2017-10-18
We present recent advances in density functional theory (DFT) for applications in the field of quantum transport, with particular emphasis on transport through strongly correlated systems. We review the foundations of the popular Landauer-Büttiker(LB) + DFT approach. This formalism, when using approximations to the exchange-correlation (xc) potential with steps at integer occupation, correctly captures the Kondo plateau in the zero bias conductance at zero temperature but completely fails to capture the transition to the Coulomb blockade (CB) regime as the temperature increases. To overcome the limitations of LB + DFT, the quantum transport problem is treated from a time-dependent (TD) perspective using TDDFT, an exact framework to deal with nonequilibrium situations. The steady-state limit of TDDFT shows that in addition to an xc potential in the junction, there also exists an xc correction to the applied bias. Open shell molecules in the CB regime provide the most striking examples of the importance of the xc bias correction. Using the Anderson model as guidance we estimate these corrections in the limit of zero bias. For the general case we put forward a steady-state DFT which is based on one-to-one correspondence between the pair of basic variables, steady density on and steady current across the junction and the pair local potential on and bias across the junction. Like TDDFT, this framework also leads to both an xc potential in the junction and an xc correction to the bias. Unlike TDDFT, these potentials are independent of history. We highlight the universal features of both xc potential and xc bias corrections for junctions in the CB regime and provide an accurate parametrization for the Anderson model at arbitrary temperatures and interaction strengths, thus providing a unified DFT description for both Kondo and CB regimes and the transition between them.
A Four Channel Beam Current Monitor Data Acquisition System Using Embedded Processors
Energy Technology Data Exchange (ETDEWEB)
Wheat, Jr., Robert Mitchell [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Dalmas, Dale A. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Dale, Gregory E. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-08-11
Data acquisition from multiple beam current monitors is required for electron accelerator production of Mo-99. A two channel system capable of recording data from two beam current monitors has been developed, is currently in use, and is discussed below. The development of a cost-effective method of extending this system to more than two channels and integrating of these measurements into an accelerator control system is the main focus of this report. Data from these current monitors is digitized, processed, and stored by a digital data acquisition system. Limitations and drawbacks with the currently deployed digital data acquisition system have been identified as have been potential solutions, or at least improvements, to these problems. This report will discuss and document the efforts we've made in improving the flexibility and lowering the cost of the data acquisition system while maintaining the minimum requirements.
Data compression/error correction digital test system. Appendix 2: Theory of operation
1972-01-01
An overall block diagram of the DC/EC digital system test is shown. The system is divided into two major units: the transmitter and the receiver. In operation, the transmitter and receiver are connected only by a real or simulated transmission link. The system inputs consist of: (1) standard format TV video, (2) two channels of analog voice, and (3) one serial PCM bit stream.
Crossover physics in the nonequilibrium dynamics of quenched quantum impurity systems.
Vasseur, Romain; Trinh, Kien; Haas, Stephan; Saleur, Hubert
2013-06-14
A general framework is proposed to tackle analytically local quantum quenches in integrable impurity systems, combining a mapping onto a boundary problem with the form factor approach to boundary-condition-changing operators introduced by Lesage and Saleur [Phys. Rev. Lett. 80, 4370 (1998)]. We discuss how to compute exactly the following two central quantities of interest: the Loschmidt echo and the distribution of the work done during the quantum quench. Our results display an interesting crossover physics characterized by the energy scale T(b) of the impurity corresponding to the Kondo temperature. We discuss in detail the noninteracting case as a paradigm and benchmark for more complicated integrable impurity models and check our results using numerical methods.
Competing effective interactions of Dirac electrons in the Spin–Fermion system
International Nuclear Information System (INIS)
Marino, E.C.; Nunes, Lizardo H.C.M.
2014-01-01
Recently discovered advanced materials, such as heavy fermions, frequently exhibit a rich phase diagram suggesting the presence of different competing interactions. A unified description of the origin of these multiple interactions, albeit very important for the comprehension of such materials is, in general not available. It would be therefore very useful to have a simple model where the common source of different interactions could be possibly traced back. In this work we consider a system consisting in a set of localized spins on a square lattice with antiferromagnetic nearest neighbors interactions and itinerant electrons, which are assumed to be Dirac-like and interact with the localized spins through a Kondo magnetic interaction. This system is conveniently described by the Spin–Fermion model, which we use in order to determine the effective interactions among the itinerant electrons. By integrating out the localized degrees of freedom we obtain a set of different interactions, which includes: a BCS-like superconducting term, a Nambu–Jona-Lasinio-like, excitonic term and a spin–spin magnetic term. The resulting phase diagram is investigated by evaluation of the mean-field free-energy as a function of the relevant order parameters. This shows the competition of the above interactions, depending on the temperature, chemical potential and coupling constants. -- Highlights: •Antiferromagnetic Heisenberg–Kondo lattice model with itinerant Dirac fermions. •Integrating out the spins generates competing interactions: BCS-like, excitonic and magnetic. •Novel mechanism of superconductivity from magnetic interactions between the spins and electrons. •Dome-shaped dependence of the temperature on the chemical potential in agreement with pnictides
Barle, Stanko
In this dissertation, two dynamical systems with many degrees of freedom are analyzed. One is the system of highly correlated electrons in the two-impurity Kondo problem. The other deals with building a realistic model of diffusion underlying financial markets. The simplest mean-field theory capable of mimicking the non-Fermi liquid behavior of the critical point in the two-impurity Kondo problem is presented. In this approach Landau's adiabaticity assumption--of a one-to-one correspondence between the low-energy excitations of the interacting and noninteracting systems--is violated through the presence of decoupled local degrees of freedom. These do not couple directly to external fields but appear indirectly in the physical properties leading, for example, to the log(T, omega) behavior of the staggered magnetic susceptibility. Also, as observed previously, the correlation function = -1/4 is a consequence of the equal weights of the singlet and triplet impurity configurations at the critical point. In the second problem, a numerical model is developed to describe the diffusion of prices in the market. Implied binomial (or multinomial) trees are constructed to enable practical pricing of derivative securities in consistency with the existing market. The method developed here is capable of accounting for both the strike price and term structure of the implied volatility. It includes the correct treatment of interest rate and dividends which proves robust even if these quantities are unusually large. The method is explained both as a set of individual innovations and, from a different prospective, as a consequence of a single plausible transformation from the tree of spot prices to the tree of futures prices.
Six-quark configurations in the NN system correlated with experiment
International Nuclear Information System (INIS)
Gorovoy, V.S.; Obukhovskij, I.T.
1996-01-01
The nucleon-nucleon interaction at short range is analyzed in terms of six-quark configuration. It is shown that in low partial waves L = 0, 1 system has a two-channel character: the N N channel and the inner six-quark state (bag) with specific color-spin structure. It is shown that polarization observables could be a good tool for investigation of a quark structure of the deuteron [ru
Nuclear magnetic resonance investigation of the heavy fermion system Ce2CoAl7Ge4
Dioguardi, A. P.; Guzman, P.; Rosa, P. F. S.; Ghimire, N. J.; Eley, S.; Brown, S. E.; Thompson, J. D.; Bauer, E. D.; Ronning, F.
2017-12-01
We present nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements performed on single crystalline Ce2CoAl7Ge4 , a member of a recently discovered family of heavy fermion materials Ce2M Al7Ge4 (M =Co , Ir, Ni, or Pd). Previous measurements indicated a strong Kondo interaction as well as magnetic order below TM=1.8 K . Our NMR spectral measurements show that the Knight shift K is proportional to the bulk magnetic susceptibility χ at high temperatures. A clear Knight shift anomaly (K ¬∝χ ) is observed at coherence temperatures T*˜17.5 K for H0∥c ̂ and 10 K for H0∥a ̂ at the 59Co site, and T*˜12.5 K at the 27Al(3) site for H0∥a ̂ characteristic of the heavy fermion nature of this compound. At high temperatures, the 59Co NMR spin-lattice relaxation rate T1-1 is dominated by spin fluctuations of the 4 f local moments with a weak metallic background. The spin fluctuations probed by 59Co NMR are anisotropic and larger in the basal plane than in the c direction. Furthermore, we find (T1T K ) -1∝T-1 /2 at the 59Co site as expected for a Kondo system for T >T* and T >TK . 59Co NQR T1-1 measurements at low temperatures indicate slowing down of spin fluctuations above the magnetic ordering temperature TM˜1.8 K . A weak ferromagnetic character of fluctuations around q =0 is evidenced by an increase of χ T versus T above the magnetic ordering temperature. We also find good agreement between the observed and calculated electric field gradients at all observed sites.
Unraveling surface enabled magnetic phenomena in low dimensional systems
Baljozovic, Milos; Girovsky, Jan; Nowakowski, Jan; Ali, Md Ehesan; Rossmann, Harald; Nijs, Thomas; Aeby, Elise; Nowakowska, Sylwia; Siewert, Dorota; Srivastava, Gitika; WäCkerlin, Christian; Dreiser, Jan; Decurtins, Silvio; Liu, Shi-Xia; Oppeneer, Peter M.; Jung, Thomas A.; Ballav, Nirmalya
Molecular spin systems with controllable interactions are of both fundamental and applied importance. These systems help us to better understand the fundamental origins of the interactions involved in low dimensional magnetic systems and to put them in the framework of existing models towards their further development. Following our first observation of exchange induced magnetic ordering in paramagnetic porphyrins adsorbed on ferromagnetic Co surface we showed that magnetic properties of such molecules can be controllably altered upon exposure to chemical and physical stimuli. In our most recent work it was shown that a synthetically programmed co-assembly of Fe and Mn phthalocyanines can also be realized on diamagnetic Au(111) surfaces where it induces long-range 2D ferrimagnetic order, at first glance in conflict with the Mermin-Wagner theory. Here we provide evidence for the first direct observation of such ordering from STM/STS and XMCD data and from DFT +U calculations demonstrating key role of the Au(111) surface states in mediating AFM RKKY coupling of the Kondo underscreened magnetic moments.
International Nuclear Information System (INIS)
Anon.
1980-01-01
Papers in this session describe the concept of mined geologic disposal system and methods for ensuring that the system, when developed, will meet all technical requirements. Also presented in the session are analyses of system parameters, such as cost and nuclear criticality potential, as well as a technical analysis of a requirement that the system permit retrieval of the waste for some period of time. The final paper discusses studies under way to investigate technical alternatives or complements to the mined geologic disposal system. Titles of the presented papers are: (1) Waste Isolation System; (2) Waste Isolation Economics; (3) BWIP Technical Baseline; (4) Criticality Considerations in Geologic Disposal of High-Level Waste; (5) Retrieving Nuclear Wastes from Repository; (6) NWTS Programs for the Evaluation of Technical Alternatives or Complements to Mined Geologic Repositories - Purpose and Objectives
Directory of Open Access Journals (Sweden)
Alexander Leonessa
2000-01-01
Full Text Available A nonlinear robust control-system design framework predicated on a hierarchical switching controller architecture parameterized over a set of moving nominal system equilibria is developed. Specifically, using equilibria-dependent Lyapunov functions, a hierarchical nonlinear robust control strategy is developed that robustly stabilizes a given nonlinear system over a prescribed range of system uncertainty by robustly stabilizing a collection of nonlinear controlled uncertain subsystems. The robust switching nonlinear controller architecture is designed based on a generalized (lower semicontinuous Lyapunov function obtained by minimizing a potential function over a given switching set induced by the parameterized nominal system equilibria. The proposed framework robustly stabilizes a compact positively invariant set of a given nonlinear uncertain dynamical system with structured parametric uncertainty. Finally, the efficacy of the proposed approach is demonstrated on a jet engine propulsion control problem with uncertain pressure-flow map data.
Comparative study of adaptive-noise-cancellation algorithms for intrusion detection systems
International Nuclear Information System (INIS)
Claassen, J.P.; Patterson, M.M.
1981-01-01
Some intrusion detection systems are susceptible to nonstationary noise resulting in frequent nuisance alarms and poor detection when the noise is present. Adaptive inverse filtering for single channel systems and adaptive noise cancellation for two channel systems have both demonstrated good potential in removing correlated noise components prior detection. For such noise susceptible systems the suitability of a noise reduction algorithm must be established in a trade-off study weighing algorithm complexity against performance. The performance characteristics of several distinct classes of algorithms are established through comparative computer studies using real signals. The relative merits of the different algorithms are discussed in the light of the nature of intruder and noise signals
A two-channel wave analyser for sounding rockets and satellites
International Nuclear Information System (INIS)
Brondz, E.
1989-04-01
Studies of low frequency electromagnetic waves, produced originally by lightning discharges penetrating the ionosphere, provide an important source of valuable information about the earth's surrounding plasma. Use of rockets and satellites supported by ground-based observations implies, unique opportunity for measuring in situ a number of parameters simultaneously in order to correlate data from various measurements. However, every rocket experiment has to be designed bearing in mind telemetry limitations and/or short flight duration. Typical flight duration for Norwegian rockets launched from Andoeya Rocket Range is 500 to 600 s. Therefore, the most desired way to use a rocket or satellite is to carry out data analyses on board in real time. Recent achievements in Digital Signal Processing (DSP) technology have made it possible to undertake very complex on board data manipulation. As a part of rocket instrumentation, a DSP based unit able to carry out on board analyses of low frequency electromagnetic waves in the ionosphere has been designed. The unit can be seen as a general purpose computer built on the basis of a fixed-point 16 bit signal processor. The unit is supplied with a program code in order to perform wave analyses on two independent channels simultaneously. The analyser is able to perform 256 point complex fast fourier transformations, and it produce a spectral power desity estimate on both channels every 85 ms. The design and construction of the DSP based unit is described and results from the tests are presented
SLOW-SPEED SUPERNOVAE FROM THE PALOMAR TRANSIENT FACTORY: TWO CHANNELS
Energy Technology Data Exchange (ETDEWEB)
White, Christopher J. [Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544 (United States); Kasliwal, Mansi M.; Piro, Anthony L. [The Observatories, Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Nugent, Peter E. [Computational Cosmology Center, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Gal-Yam, Avishay; Ofek, Eran O.; Ben-Ami, Sagi [Benoziyo Center for Astrophysics, The Weizmann Institute of Science, Rehovot 76100 (Israel); Howell, D. Andrew [Department of Physics, University of California, Santa Barbara, Broida Hall, Mail Code 9530, Santa Barbara, CA 93106-9530 (United States); Sullivan, Mark [School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ (United Kingdom); Goobar, Ariel [The Oskar Klein Centre, Department of Physics, AlbaNova, Stockholm University, SE-106 91 Stockholm (Sweden); Bloom, Joshua S. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Kulkarni, Shrinivas R.; Cao, Yi [Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Laher, Russ R.; Masci, Frank; Surace, Jason [Spitzer Science Center, California Institute of Technology, M/S 314-6, Pasadena, CA 91125 (United States); Cenko, S. Bradley [Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771 (United States); Hook, Isobel M. [Department of Physics (Astrophysics), University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom); Jönsson, Jakob [Savantic AB, Rosenlundsgatan 50, SE-118 63 Stockholm (Sweden); Matheson, Thomas [National Optical Astronomy Observatory, Tucson, AZ 85719-4933 (United States); and others
2015-01-20
Since the discovery of the unusual prototype SN 2002cx, the eponymous class of Type I (hydrogen-poor) supernovae with low ejecta speeds has grown to include approximately two dozen members identified from several heterogeneous surveys, in some cases ambiguously. Here we present the results of a systematic study of 1077 Type I supernovae discovered by the Palomar Transient Factory, leading to nine new members of this peculiar class. Moreover, we find there are two distinct subclasses based on their spectroscopic, photometric, and host galaxy properties: ''SN 2002cx-like'' supernovae tend to be in later-type or more irregular hosts, have more varied and generally dimmer luminosities, have longer rise times, and lack a Ti II trough when compared to ''SN 2002es-like'' supernovae. None of our objects show helium, and we counter a previous claim of two such events. We also find that the occurrence rate of these transients relative to Type Ia supernovae is 5.6{sub −3.8}{sup +22}% (90% confidence), lower compared to earlier estimates. Combining our objects with the literature sample, we propose that these subclasses have two distinct physical origins.
The design of two channel IIR QMF bank directly from analogue prototype
Stamenković, N.; Stojanovuć, V.
2011-07-01
This article presents a new method for designing two-band quadrature mirror filter (QMF) banks. Analytic solution of the filter coefficients is obtained in the s-domain. The characteristic function of the new filter has one multiple pole in the pass-band and one multiple zero in the stop-band. As a consequence, the transfer function has a single ripple, both in the pass-band and in the stop-band. Lowpass and highpass filter pair is double complementary in the s-plane. The gain responses of the lowpass and highpass filter pair at the crossover frequency are approximately 3 dB below their maximum values. Using the bilinear transformation, the analogue filter transfer function is mapped into the corresponding digital filter transfer function, so that the analogue crossover frequency is mapped into the digital frequency corresponding to ω = π/2. The filter characteristic exhibits Butterworth-like behaviour near the origin and Chebyshev-like behaviour (of the third order) near the pass-band edge.
Distributed Nonstationary Heat Model of Two-Channel Solar Air Heater
International Nuclear Information System (INIS)
Klychev, Sh. I.; Bakhramov, S. A.; Ismanzhanov, A. I.; Tashiev, N.N.
2011-01-01
An algorithm for a distributed nonstationary heat model of a solar air heater (SAH) with two operating channels is presented. The model makes it possible to determine how the coolant temperature changes with time along the solar air heater channel by considering its main thermal and ambient parameters, as well as variations in efficiency. Examples of calculations are presented. It is shown that the time within which the mean-day efficiency of the solar air heater becomes stable is significantly higher than the time within which the coolant temperature reaches stable values. The model can be used for investigation of the performances of solar water-heating collectors. (authors)
Design of Two-channel Half-band Bank of Digital Filters using Optimization Methods
Czech Academy of Sciences Publication Activity Database
Gescheidtová, E.; Kubásek, J.; Smékal, Z.; Bartušek, Karel
2007-01-01
Roč. 40, č. 1 (2007), s. 71-79 ISSN 1738-6438 R&D Projects: GA ČR(CZ) GA102/07/0389; GA ČR(CZ) GA102/07/1086 Institutional research plan: CEZ:AV0Z20650511 Keywords : criterial function * transfer function * bank of digital filters Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering
Two ghrelin receptor (GHS-R) genes were isolated from channel catfish tissue and a bacterial artificial chromosome (BAC) library. The two receptors were characterized by determining tissue distribution, ontogeny of receptor mRNA expression, and effects of exogenous homologous ghrelin administration ...
Introducing Filters and Amplifiers Using a Two-Channel Light Organ
Zavrel, Erik; Sharpsteen, Eric
2015-01-01
In an era when many students carry iPods, iPhones, and iPads, physics teachers are realizing that in order to continue to inspire and convey the amazing things made possible by a few fundamental principles, they must expand laboratory coverage of electricity and circuits beyond the conventional staples of constructing series and parallel…
A two-channel, spectrally degenerate polarization entangled source on chip
Sansoni, Linda; Luo, Kai Hong; Eigner, Christof; Ricken, Raimund; Quiring, Viktor; Herrmann, Harald; Silberhorn, Christine
2017-12-01
Integrated optics provides the platform for the experimental implementation of highly complex and compact circuits for quantum information applications. In this context integrated waveguide sources represent a powerful resource for the generation of quantum states of light due to their high brightness and stability. However, the confinement of the light in a single spatial mode limits the realization of multi-channel sources. Due to this challenge one of the most adopted sources in quantum information processes, i.e. a source which generates spectrally indistinguishable polarization entangled photons in two different spatial modes, has not yet been realized in a fully integrated platform. Here we overcome this limitation by suitably engineering two periodically poled waveguides and an integrated polarization splitter in lithium niobate. This source produces polarization entangled states with fidelity of F = 0.973 ±0.003 and a test of Bell's inequality results in a violation larger than 14 standard deviations. It can work both in pulsed and continuous wave regime. This device represents a new step toward the implementation of fully integrated circuits for quantum information applications.
Active RC filter based implementation analysis part of two channel hybrid filter bank
Directory of Open Access Journals (Sweden)
Stojanović Vidosav
2014-01-01
Full Text Available In the present paper, a new design method for continuous-time powersymmetric active RC filters for Hybrid Filter Bank (HFB is proposed. Some theoretical properties of continious-time power-symmetric filters bank in a more general perspective are studied. This includes the derivation of a new general analytical form, and a study of poles and zeros locations in s-plane. In the proposed design method the analytic solution of filter coefficients is solved in sdomain using only one nonlinear equation Finally, the proposed approximation is compared to standard approximations. It was shown that attenuation and group delay characteristic of the proposed filter lie between Butterworth and elliptic characteristics. [Projekat Ministarstva nauke Republike Srbije, br. 32009TR
Kuldeep, B; Singh, V K; Kumar, A; Singh, G K
2015-01-01
In this article, a novel approach for 2-channel linear phase quadrature mirror filter (QMF) bank design based on a hybrid of gradient based optimization and optimization of fractional derivative constraints is introduced. For the purpose of this work, recently proposed nature inspired optimization techniques such as cuckoo search (CS), modified cuckoo search (MCS) and wind driven optimization (WDO) are explored for the design of QMF bank. 2-Channel QMF is also designed with particle swarm optimization (PSO) and artificial bee colony (ABC) nature inspired optimization techniques. The design problem is formulated in frequency domain as sum of L2 norm of error in passband, stopband and transition band at quadrature frequency. The contribution of this work is the novel hybrid combination of gradient based optimization (Lagrange multiplier method) and nature inspired optimization (CS, MCS, WDO, PSO and ABC) and its usage for optimizing the design problem. Performance of the proposed method is evaluated by passband error (ϕp), stopband error (ϕs), transition band error (ϕt), peak reconstruction error (PRE), stopband attenuation (As) and computational time. The design examples illustrate the ingenuity of the proposed method. Results are also compared with the other existing algorithms, and it was found that the proposed method gives best result in terms of peak reconstruction error and transition band error while it is comparable in terms of passband and stopband error. Results show that the proposed method is successful for both lower and higher order 2-channel QMF bank design. A comparative study of various nature inspired optimization techniques is also presented, and the study singles out CS as a best QMF optimization technique. Copyright © 2014 ISA. Published by Elsevier Ltd. All rights reserved.
Two-channel spin-chain communication line and simple quantum gates
Stolze, J.; Zenchuk, A. I.
2017-08-01
We consider the remote creation of a mixed state in a one-qubit receiver connected to two two-qubit senders via different channels. Channels are assumed to be chains of spins (qubits) with nearest-neighbor interactions, no external fields are being applied. The problem of sharing the creatable region of the receiver's state-space between two senders is considered for a communication line with the receiver located asymmetrically with respect to these senders (asymmetric communication line). An example of a quantum register realizing simple functions is constructed on the basis of a symmetric communication line. In that setup, the initial states of the two senders serve as input and control signals, respectively, while the state of the receiver at a proper time instant is considered as the output signal.
Robust Sounds of Activities of Daily Living Classification in Two-Channel Audio-Based Telemonitoring
Directory of Open Access Journals (Sweden)
David Maunder
2013-01-01
Full Text Available Despite recent advances in the area of home telemonitoring, the challenge of automatically detecting the sound signatures of activities of daily living of an elderly patient using nonintrusive and reliable methods remains. This paper investigates the classification of eight typical sounds of daily life from arbitrarily positioned two-microphone sensors under realistic noisy conditions. In particular, the role of several source separation and sound activity detection methods is considered. Evaluations on a new four-microphone database collected under four realistic noise conditions reveal that effective sound activity detection can produce significant gains in classification accuracy and that further gains can be made using source separation methods based on independent component analysis. Encouragingly, the results show that recognition accuracies in the range 70%–100% can be consistently obtained using different microphone-pair positions, under all but the most severe noise conditions.
[Realistic theories of heavy electron and other strongly correlated materials
International Nuclear Information System (INIS)
1993-01-01
Research on the following topics is summarized: non-perturbative treatments of multi-channel Kondo models, non-perturbative treatments of multi-band models for the quadrupolar fluctuation model of the cuprates, extension of the two-channel Kondo model to other materials and treatment of the infinite-dimensional Hubbard model within the Non-crossing approximation. Data on the specific heat of Y 0.8 U 0.2 Pd 3 and the c-axis susceptibility and specific heat of U in ThRu 2 Si are shown. 5 figs., 84 refs
Detector-counter scintillator with data acquisition system for industrial processes control
International Nuclear Information System (INIS)
Costa, Fabio Eduardo da; Hamada, Margarida Mizue; mmhamada@net@ipen.br
2000-01-01
Detectors using silicon photodiodes coupled to CsI(Tl) crystals are a technically feasible option for portable detection systems for ionizing radiation. The photodiodes are advantageous because they are not sensitive to magnetic fields, may be operated by low bias and their efficiency spectrum has a good match with the CsI(Tl) crystals spectrum. With this technology, a two channel detection system was developed, associated to a laptop or notebook computer. This system constitutes an autonomous unit to count radioactive, in real time, at two sites, which may be up to 60 meters far from each other. (author)
Solution of the effective Hamiltonian of impurity hopping between two sites in a metal
Ye, Jinwu
1997-07-01
We analyze in detail all the possible fixed points of the effective Hamiltonian of a nonmagnetic impurity hopping between two sites in a metal obtained by Moustakas and Fisher (MF). We find a line of non-Fermi liquid fixed points which continuously interpolates between the two-channel Kondo fixed point (2CK) and the one-channel, two-impurity Kondo (2IK) fixed point. There is one relevant direction with scaling dimension 12 and one leading irrelevant operator with dimension 32. There is also one marginal operator in the spin sector moving along this line. The marginal operator, combined with the leading irrelevant operator, will generate the relevant operator. For the general position on this line, the leading low-temperature exponents of the specific heat, the hopping susceptibility and the electron conductivity Cimp,χhimp,σ(T) are the same as those of the 2CK, but the finite-size spectrum depends on the position on the line. No universal ratios can be formed from the amplitudes of the three quantities except at the 2CK point on this line where the universal ratios can be formed. At the 2IK point on this line, σ(T)~2σu(1+aT3/2), no universal ratio can be formed either. The additional non-Fermi-liquid fixed point found by MF has the same symmetry as the 2IK, it has two relevant directions with scaling dimension 12, and is therefore also unstable. The leading low-temperature behaviors are Cimp~T,χhimp~lnT,σ(T)~2σu(1+aT3/2) no universal ratios can be formed. The system is shown to flow to a line of Fermi-liquid fixed points which continuously interpolates between the noninteracting fixed point and the two-channel spin-flavor Kondo fixed point discussed by the author previously. The effect of particle-hole symmetry breaking is discussed. The effective Hamiltonian in the external magnetic field is analyzed. The scaling functions for the physical measurable quantities are derived in the different regimes; their predictions for the experiments are given. Finally
An automated miniature robotic vehicle inspection system
Energy Technology Data Exchange (ETDEWEB)
Dobie, Gordon; Summan, Rahul; MacLeod, Charles; Pierce, Gareth; Galbraith, Walter [Centre for Ultrasonic Engineering, University of Strathclyde, 204 George Street, Glasgow, G1 1XW (United Kingdom)
2014-02-18
A novel, autonomous reconfigurable robotic inspection system for quantitative NDE mapping is presented. The system consists of a fleet of wireless (802.11g) miniature robotic vehicles, each approximately 175 × 125 × 85 mm with magnetic wheels that enable them to inspect industrial structures such as storage tanks, chimneys and large diameter pipe work. The robots carry one of a number of payloads including a two channel MFL sensor, a 5 MHz dry coupled UT thickness wheel probe and a machine vision camera that images the surface. The system creates an NDE map of the structure overlaying results onto a 3D model in real time. The authors provide an overview of the robot design, data fusion algorithms (positioning and NDE) and visualization software.
An automated miniature robotic vehicle inspection system
International Nuclear Information System (INIS)
Dobie, Gordon; Summan, Rahul; MacLeod, Charles; Pierce, Gareth; Galbraith, Walter
2014-01-01
A novel, autonomous reconfigurable robotic inspection system for quantitative NDE mapping is presented. The system consists of a fleet of wireless (802.11g) miniature robotic vehicles, each approximately 175 × 125 × 85 mm with magnetic wheels that enable them to inspect industrial structures such as storage tanks, chimneys and large diameter pipe work. The robots carry one of a number of payloads including a two channel MFL sensor, a 5 MHz dry coupled UT thickness wheel probe and a machine vision camera that images the surface. The system creates an NDE map of the structure overlaying results onto a 3D model in real time. The authors provide an overview of the robot design, data fusion algorithms (positioning and NDE) and visualization software
Directory of Open Access Journals (Sweden)
K. Swarnalatha
2013-01-01
Full Text Available Risk analysis of urban aquatic systems due to heavy metals turns significant due to their peculiar properties viz. persis tence, non-degradab ility, toxicity, and accumulation. Akkulam Veli (AV, an urba n tropical lake in south India is subjected to various environmental stresses due to multiple waste discharge, sand mining, developmental activities, tour ism related activitie s etc. Hence, a comprehensive approach is adopted for risk assessment using modified degree of contamination factor, toxicity units based on numerical sediment quality guidelines (SQGs, and potentialecological risk indices. The study revealed the presence of toxic metals such as Cr, C d, Pb and As and the lake is rated under ‘low ecological risk’ category.
Valence skipping driven superconductivity and charge Kondo effect
International Nuclear Information System (INIS)
Yanagisawa, Takashi; Hase, Izumi
2013-01-01
Highlights: •Valence skipping in metallic compounds can give rise to an unconventional superconductivity. •Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. •The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. •We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. •There is a high temperature region near the boundary. -- Abstract: Valence skipping in metallic compounds can give rise to an unconventional superconductivity. Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. The superconducting state is changed into a metallic state with a local singlet as the attractive interaction |U| increases. There is a high temperature region near the boundary
EDITORIAL: Strongly correlated electron systems Strongly correlated electron systems
Ronning, Filip; Batista, Cristian
2011-03-01
-dependent Zeeman splitting in strontium ruthenate Emil J Rozbicki, James F Annett, Jean-René Souquet and Andrew P Mackenzie Thermodynamics of itinerant metamagnetic transitions A M Berridge Magnon-mediated pairing and isotope effect in iron-based superconductors Jiansheng Wu and Philip Phillips Nernst quantum oscillations in bulk semi-metals Zengwei Zhu, Huan Yang, Aritra Banerjee, Liam Malone, Benoît Fauqué and Kamran Behnia Signatures of a quantum Griffiths phase in a d-metal alloy close to its ferromagnetic quantum critical point Almut Schroeder, Sara Ubaid-Kassis and Thomas Vojta Influence of super-ohmic dissipation on a disordered quantum critical point Thomas Vojta, José A Hoyos, Priyanka Mohan and Rajesh Narayanan The van Hemmen-Kondo model for disordered cerium systems S G Magalhaes, F M Zimmer and B Coqblin Chemical pressure, dilution and disorder in the heavy fermion compounds Ce3 - xLaxPd20Si6 (x = 1/3, 2/3) H Winkler, K-A Lorenzer, S Laumann, J Custers, A Prokofiev and S Paschen Magnetism of fine particles of Kondo lattices, obtained by high-energy ball-milling E V Sampathkumaran, K Mukherjee, Kartik K Iyer, Niharika Mohapatra and Sitikantha D Das Heavy fermion scaling: uranium versus cerium and ytterbium compounds J M Lawrence, C H Wang, A D Christianson and E D Bauer Temperature dependence of hybridization gaps in metallic heavy-fermion systems Xiaodong Yang, Peter S Riseborough and Tomasz Durakiewicz Low-energy properties of the Kondo lattice model O Bodensiek, R Žitko, R Peters and T Pruschke Temperature dependence of the zero-bias anomaly in the Anderson-Hubbard model: insights from an ensemble of two-site systems R Wortis and W A Atkinson A charge density wave in the hidden order state of URu2Si2 Jung-Jung Su, Yonatan Dubi, Peter Wölfle and Alexander V Balatsky Field-induced suppression of the heavy-fermion state in YbRh2Si2 Gertrud Zwicknagl Discontinuous Hall coefficient at the quantum critical point in YbRh2Si2 Sven Friedemann, Niels Oeschler, Steffen
The NMR probe of high-Tc materials and correlated electron systems. 2. ed.
International Nuclear Information System (INIS)
Walstedt, Russell E.
2018-01-01
This new edition updates readers in three areas of NMR studies, namely, recent developments in high-T c materials, heavy fermion systems and actinide oxides are presented. The NMR probe has yielded a vast array of data for solid state materials, corresponding to different compounds, ionic sites, and nuclear species, as well as to a wide variety of experimental conditions. The last two parts of the book are completely new in this edition, while the first part has seen major updates. This edition features the latest developments for high-T c materials, especially the advances in the area of pseudogap studies are reviewed. An in depth overview of heavy fermion systems is presented in the second part, notably Kondo lattices, quantum critical points and unconventional superconductivity are areas of intense research recently and are covered extensively. Finally, valuable information from NMR studies with actinide oxides will be provided. Ongoing analysis and discussion of NMR data have resulted in a wealth of important insights into the physics of these exotic systems. The aims of this monograph are manifold. First, it reviews NMR methodology as it has been applied to the different studies. This is addressed to NMR practitioners and to physics laypersons alike. Next, it presents a review of NMR measurements and the wide variety of phenomena which they represent. The third phase is to recount the theoretical model calculations and other proposals which have been put forward to account for these data.
The NMR probe of high-T{sub c} materials and correlated electron systems. 2. ed.
Energy Technology Data Exchange (ETDEWEB)
Walstedt, Russell E. [Michigan Univ., Ann Arbor, MI (United States). Dept. of Physics
2018-03-01
This new edition updates readers in three areas of NMR studies, namely, recent developments in high-T{sub c} materials, heavy fermion systems and actinide oxides are presented. The NMR probe has yielded a vast array of data for solid state materials, corresponding to different compounds, ionic sites, and nuclear species, as well as to a wide variety of experimental conditions. The last two parts of the book are completely new in this edition, while the first part has seen major updates. This edition features the latest developments for high-T{sub c} materials, especially the advances in the area of pseudogap studies are reviewed. An in depth overview of heavy fermion systems is presented in the second part, notably Kondo lattices, quantum critical points and unconventional superconductivity are areas of intense research recently and are covered extensively. Finally, valuable information from NMR studies with actinide oxides will be provided. Ongoing analysis and discussion of NMR data have resulted in a wealth of important insights into the physics of these exotic systems. The aims of this monograph are manifold. First, it reviews NMR methodology as it has been applied to the different studies. This is addressed to NMR practitioners and to physics laypersons alike. Next, it presents a review of NMR measurements and the wide variety of phenomena which they represent. The third phase is to recount the theoretical model calculations and other proposals which have been put forward to account for these data.
An on-line dilution system for spectrometry using an inductively coupled plasma source
International Nuclear Information System (INIS)
Moore, G.L.; Watson, A.E.; Humphries-Cuff, P.J.
1982-01-01
An on-line dilution system that uses a two-channel peristaltic pump to feed a GMK Babington type of nebulizer is described. By the use of a diluent containing the appropriate concentrations of acid, sodium, and internal standard element, which was fed at a constant rate to the nebulizer, the system produced analytical results that are not significantly different (less than 3 per cent relative) from those obtained with the normal dilution technique. However, a considerable saving in time is achieved, as well as a saving in the use of expensive reagents
Phase separation in strongly correlated electron systems with two types of charge carriers
International Nuclear Information System (INIS)
Kugel, K.I.; Rakhmanov, A.L.; Sboychakov, A.O.
2007-01-01
Full text: A competition between the localization of the charge carriers due to Jahn-Teller distortions and the energy gain due to their delocalization in doped manganite and related magnetic oxides is analyzed based on a Kondo-lattice type model. The resulting effective Hamiltonian is, in fact, a generalization of the Falicov-Kimball model. We find that the number of itinerant charge carriers can be significantly lower than that implied by the doping level x. The phase diagram of the model in the T plane is constructed. The system exhibits magnetic ordered (antiferromagnetic, ferromagnetic, or canted) states as well the paramagnetic states with zero and nonzero density of the itinerant electrons. It is shown that a phase-separation is favorable in energy for a wide doping range. The characteristic size of inhomogeneities in a phase-separated state is of the order of several lattice constants. We also analyzed the two-band Hubbard model in the limit of strong on-site Coulomb repulsion. It was shown that such a system has a tendency to phase separation into the regions with different charge densities even in the absence of magnetic or any other ordering, if the ratio of the bandwidths is large enough. The work was supported by the European project CoMePhS and by the Russian Foundation for Basic Research, project no. 05-02-17600. (authors)
The NMR probe of high-Tc materials and correlated electron systems
Walstedt, Russell E
2018-01-01
This new edition updates readers in three areas of NMR studies, namely, recent developments in high-Tc materials, heavy fermion systems and actinide oxides are presented. The NMR probe has yielded a vast array of data for solid state materials, corresponding to different compounds, ionic sites, and nuclear species, as well as to a wide variety of experimental conditions. The last two parts of the book are completely new in this edition, while the first part has seen major updates. This edition features the latest developments for high-Tc materials, especially the advances in the area of pseudogap studies are reviewed. An in depth overview of heavy fermion systems is presented in the second part, notably Kondo lattices, quantum critical points and unconventional superconductivity are areas of intense research recently and are covered extensively. Finally, valuable information from NMR studies with actinide oxides will be provided. Ongoing analysis and discussion of NMR data have resulted in a wealth o...
Quantum dot systems: artificial atoms with tunable properties
International Nuclear Information System (INIS)
Weis, J.
2005-01-01
Full text: Quantum dots - also called zero-dimensional electron systems or artificial atoms - are physical objects where the constituent electrons are confined in a small spatial region, leading to discrete eigenvalues for the energies of the confined electrons. Large quantum dots offer a dense energy spectrum comparable to that of metallic grains, whereas small quantum dots more closely resemble atoms in their electronic properties. Quantum dots can be linked to leads by tunnel barriers, hence permitting electrical transport measurements: Coulomb blockade and single-electron charging effects are observed due to the repulsive electron electron interaction on the quantum dot site. Usually fabricated by conventional semiconductor growth and processing technology, the advantage is that both simple and also more complex quantum dot systems can be designed to purpose, acting as model systems with in-situ tunable parameters such as the number of confined electrons in the quantum dot and the strength of the tunnel coupling to the leads, electrostatically controlled by the applied voltages to gate electrodes. With increasing the tunnel coupling to the leads, the virtual occupation of the quantum dot from the leads becomes more and more important -- the simple description of electrical transport by single-electron tunneling events breaks down. The basic physics is described by the Kondo physics based on the Anderson impurity model. A system consisting of strongly electrostatically coupled quantum dots with separate leads to each quantum dot represent another realization of the Anderson impurity model. Experiments to verify the analogy are presented. The experimental data embedded within this tutorial have been obtained with Alexander Huebel, Matthias Keller, Joerg Schmid, David Quirion, Armin Welker, Ulf Wilhelm, and Klaus von Klitzing. (author)
Energy Technology Data Exchange (ETDEWEB)
Rahman, S; Timlin, J; Crow, J E; Mihalisin, T; Schlottmann, P [Temple Univ., Philadelphia, PA (United States)
1990-01-01
CePb{sub 3} is an itinerant heavy fermion antiferromagnetic displaying an incommensurate magnetic structure and an extremely small ordered moment. CeIn{sub 3} and CeTl{sub 3}, on the other hand are well-localized, simple antiferromagnets with the full moments expected for crystal field doublet Ce{sup 3+} ion systems. The authors have performed specific heat, sysceptibility and resistivity measurements for both the Ce(Pb,In){sub 3} and Ce(Pb,Tl){sub 3} systems. These systems remain cubic Cu{sub 3}Au structures across the entire series. They display extremely interesting T{sub N} behavior which suggests that a continuous transition from itinerant to localized antiferromagnetic behavior occurs for the Ce(Pb,Tl){sub 3} system. In the Ce (Pb,In){sub 3} system both types of antiferromagnetism are present but they are separated by a concentration range ({approximately}10-40% Pb) over which antiferromagnetism does not exist. The behavior of these systems cannot be accounted for by a Kondo necklace approach that neglects the coherence of a heavy fermion lattice and resulting itinerant antiferromagnetism.
Dynamics of the fusion reaction in the dtμ- system
International Nuclear Information System (INIS)
Belyaev, V.B.; Revai, J.; Zubarev, A.L.
1988-08-01
A dynamical scheme based on the (td,αn) two-channel model is derived for the description of the fusion reaction in the dtμ - system. Special attention is paid to the correct specification of the final states. Several possibilities are pointed out for the systematic improvement of the sudden approximation for the sticking coefficient. It seems to be useful to outline a general formulation of these processes which would allow a clear comparison of existing approaches. The lack of satisfactory agreement between experimental and theoretical values of the sticking coefficient is a further argument in favour of the programme. (R.P.) 10 refs
Numerical methods and applications in many fermion systems
Energy Technology Data Exchange (ETDEWEB)
Luitz, David J.
2013-02-07
This thesis presents results covering several topics in correlated many fermion systems. A Monte Carlo technique (CT-INT) that has been implemented, used and extended by the author is discussed in great detail in chapter 3. The following chapter discusses how CT-INT can be used to calculate the two particle Green's function and explains how exact frequency summations can be obtained. A benchmark against exact diagonalization is presented. The link to the dynamical cluster approximation is made in the end of chapter 4, where these techniques are of immense importance. In chapter 5 an extensive CT-INT study of a strongly correlated Josephson junction is shown. In particular, the signature of the first order quantum phase transition between a Kondo and a local moment regime in the Josephson current is discussed. The connection to an experimental system is made with great care by developing a parameter extraction strategy. As a final result, we show that it is possible to reproduce experimental data from a numerically exact CT-INT model-calculation. The last topic is a study of graphene edge magnetism. We introduce a general effective model for the edge states, incorporating a complicated interaction Hamiltonian and perform an exact diagonalization study for different parameter regimes. This yields a strong argument for the importance of forbidden umklapp processes and of the strongly momentum dependent interaction vertex for the formation of edge magnetism. Additional fragments concerning the use of a Legendre polynomial basis for the representation of the two particle Green's function, the analytic continuation of the self energy for the Anderson Kane Mele Model as well as the generation of test data with a given covariance matrix are documented in the appendix. A final appendix provides some very important matrix identities that are used for the discussion of technical details of CT-INT.
Numerical methods and applications in many fermion systems
International Nuclear Information System (INIS)
Luitz, David J.
2013-01-01
This thesis presents results covering several topics in correlated many fermion systems. A Monte Carlo technique (CT-INT) that has been implemented, used and extended by the author is discussed in great detail in chapter 3. The following chapter discusses how CT-INT can be used to calculate the two particle Green's function and explains how exact frequency summations can be obtained. A benchmark against exact diagonalization is presented. The link to the dynamical cluster approximation is made in the end of chapter 4, where these techniques are of immense importance. In chapter 5 an extensive CT-INT study of a strongly correlated Josephson junction is shown. In particular, the signature of the first order quantum phase transition between a Kondo and a local moment regime in the Josephson current is discussed. The connection to an experimental system is made with great care by developing a parameter extraction strategy. As a final result, we show that it is possible to reproduce experimental data from a numerically exact CT-INT model-calculation. The last topic is a study of graphene edge magnetism. We introduce a general effective model for the edge states, incorporating a complicated interaction Hamiltonian and perform an exact diagonalization study for different parameter regimes. This yields a strong argument for the importance of forbidden umklapp processes and of the strongly momentum dependent interaction vertex for the formation of edge magnetism. Additional fragments concerning the use of a Legendre polynomial basis for the representation of the two particle Green's function, the analytic continuation of the self energy for the Anderson Kane Mele Model as well as the generation of test data with a given covariance matrix are documented in the appendix. A final appendix provides some very important matrix identities that are used for the discussion of technical details of CT-INT.
Introduction to integrable many-body systems III
International Nuclear Information System (INIS)
Bajnok, Z.; Samaj, L.
2011-01-01
This is the third part of a three-volume introductory course about integrable systems of interacting bodies. The emphasis is put onto the method of Thermodynamic Bethe Ansatz. Two kinds of integrable models are studied. Systems of itinerant electrons, forming a part of Condensed Matter Physics, involve the Hubbard lattice model of electrons with short-ranged one-site interactions (Sect. 20) and the s-d exchange Kondo model (Sect. 21), describing the scattering of conduction electrons on a spin-s impurity. Methods and basic concepts used in Quantum Field Theory are explained on the integrable (1 + 1)-dimensional sine-Gordon model. We start with the classical description of the model in Sect. 22, analyze its finite energy field configurations (soliton, anti-soliton and breathers) and show its classical integrability. The model is quantized by using two schemes: the conformal (Sect. 23) and Lagrangian (Sect. 24) quantizations. The scattering matrix of the sine-Gordon theory is derived at the full quantum level in the bootstrap scheme and is compared to its classical limit in Sect. 25. The parameters of the scattering matrix are related to those of the Lagrangian by calculating the ground-state energy in an applied magnetic field in two ways: Conformal perturbation theory and Thermodynamic Bethe Ansatz (Sect. 26). The relation of the sine-Gordon theory to the XXZ Heisenberg model, which provides a complete solution of the sine-Gordon model in a finite volume, is pointed out in Sect. 27. The obtained results are applied in Sect. 28. to the derivation of the exact thermodynamics for the (symmetric) two-component Coulomb gas; this is the first classical two-dimensional fluid with exactly solvable thermodynamics (Authors)
Radiodiagnostic system combining scintillation GKS-2 γ camera and SAORI-01 computerized unit
International Nuclear Information System (INIS)
Kalashnikov, S.D.; Mishchenko, S.V.; Chuprov, P.V.
1986-01-01
A medical radiodiagnostic system prising the GKS-2 scintillation gamma chamber and the on-line data processing system is described. The gamma chamber consists of a detector, a two-channel control console, a microprocessor system for correction of distortions,system of photographic recording of images from an oscilloscopic display, a digital display-monitor and 6 accessiory collimators with trucks. GKS-2 has the increased spatial resolution, fast response and image homogeneity. Application of GKS-2 together with the SAORI-01 specialized on-line system,comprising the measuring computerized system, the colour-graphic display controller the polarizer photographic recording device for scanning image from the display screen and a system of base software, expands substantially diagnostic possibilities of equipment
Correlation effects in side-coupled quantum dots
International Nuclear Information System (INIS)
Zitko, R; Bonca, J
2007-01-01
Using Wilson's numerical renormalization group (NRG) technique, we compute zero-bias conductance and various correlation functions of a double quantum dot (DQD) system. We present different regimes within a phase diagram of the DQD system. By introducing a negative Hubbard U on one of the quantum dots, we simulate the effect of electron-phonon coupling and explore the properties of the coexisting spin and charge Kondo state. In a triple quantum dot (TQD) system, a multi-stage Kondo effect appears where localized moments on quantum dots are screened successively at exponentially distinct Kondo temperatures
Dehybridization of f and d states in the heavy-fermion system YbRh2Si2
Leuenberger, D.; Sobota, J. A.; Yang, S.-L.; Pfau, H.; Kim, D.-J.; Mo, S.-K.; Fisk, Z.; Kirchmann, P. S.; Shen, Z.-X.
2018-04-01
We report an optically induced reduction of the f -d hybridization in the prototypical heavy-fermion compound YbRh2Si2 . We use femtosecond time- and angle-resolved photoemission spectroscopy to monitor changes of spectral weight and binding energies of the Yb 4 f and Rh 4 d states before the lattice temperature increases after pumping. Overall, the f -d hybridization decreases smoothly with increasing electronic temperature up to ˜250 K but changes slope at ˜100 K . This temperature scale coincides with the onset of coherent Kondo scattering and with thermally populating the first excited crystal electrical field level. Extending previous photoemission studies, we observe a persistent f -d hybridization up to at least ˜250 K , which is far larger than the coherence temperature defined by transport but in agreement with the temperature dependence of the noninteger Yb valence. Our data underlines the distinction of probes accessing spin and charge degrees of freedom in strongly correlated systems.
Ichiki, Katsuya; Mimura, Kojiro; Anzai, Hiroaki; Uozumi, Takayuki; Sato, Hitoshi; Utsumi, Yuki; Ueda, Shigenori; Mitsuda, Akihiro; Wada, Hirofumi; Taguchi, Yukihiro; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki
2017-07-01
We investigated the bulk-derived electronic structure of the temperature-induced valence transition system EuNi2(Si1 -xGex )2 (x =0.70 , 0.79, and 0.82) by means of hard x-ray photoemission spectroscopy (HAXPES). The HAXPES spectra clearly show distinct temperature dependencies in the spectral intensities of the Eu2 + and Eu3 +3 d components. For x =0.70 , the changes in the Eu2 + and Eu3 +3 d spectral components with temperature reflect a continuous valence transition, whereas the sudden changes for x =0.79 and 0.82 reflect first-order valence transitions. The Eu 3 d spectral shapes for all x and particularly the drastic changes in the Eu3 +3 d feature with temperature are validated by a theoretical calculation based on the single-impurity Anderson model (SIAM). SIAM analysis reveals that the valence transition for each x is controlled by the c -f hybridization strength and the charge-transfer energy. Furthermore, the c -f hybridization strength governs the valence transition of this system, which is either first order or continuous, consistent with Kondo volume collapse.
International Nuclear Information System (INIS)
Geogdzhayev, Igor V.; Mishchenko, Michael I.; Liu Li; Remer, Lorraine
2004-01-01
We present an update on the status of the global climatology of the aerosol column optical thickness and Angstrom exponent derived from channel-1 and -2 radiances of the Advanced Very High Resolution Radiometer (AVHRR) in the framework of the Global Aerosol Climatology Project (GACP). The latest version of the climatology covers the period from July 1983 to September 2001 and is based on an adjusted value of the diffuse component of the ocean reflectance as derived from extensive comparisons with ship sun-photometer data. We use the updated GACP climatology and Stratospheric Aerosol and Gas Experiment (SAGE) data to analyze how stratospheric aerosols from major volcanic eruptions can affect the GACP aerosol product. One possible retrieval strategy based on the AVHRR channel-1 and -2 data alone is to infer both the stratospheric and the tropospheric aerosol optical thickness while assuming fixed microphysical models for both aerosol components. The second approach is to use the SAGE stratospheric aerosol data in order to constrain the AVHRR retrieval algorithm. We demonstrate that the second approach yields a consistent long-term record of the tropospheric aerosol optical thickness and Angstrom exponent. Preliminary comparisons of the GACP aerosol product with MODerate resolution Imaging Spectrometer (MODIS) and Multiangle Imaging Spectro-Radiometer aerosol retrievals show reasonable agreement, the GACP global monthly optical thickness being lower than the MODIS one by approximately 0.03. Larger differences are observed on a regional scale. Comparisons of the GACP and MODIS Angstrom exponent records are less conclusive and require further analysis
International Nuclear Information System (INIS)
Oliveira, A.C.J.G. de.
1988-12-01
Sensitivity calculations are very important in design and safety of nuclear reactor cores. Large codes with a great number of physical considerations have been used to perform sensitivity studies. However, these codes need long computation time involving high costs. The perturbation theory has constituted an efficient and economical method to perform sensitivity analysis. The present work is an application of the perturbation theory (matricial formalism) to a simplified model of DNB (Departure from Nucleate Boiling) analysis to perform sensitivity calculations in PWR cores. Expressions to calculate the sensitivity coefficients of enthalpy and coolant velocity with respect to coolant density and hot channel area were developed from the proposed model. The CASNUR.FOR code to evaluate these sensitivity coefficients was written in Fortran. The comparison between results obtained from the matricial formalism of perturbation theory with those obtained directly from the proposed model makes evident the efficiency and potentiality of this perturbation method for nuclear reactor cores sensitivity calculations (author). 23 refs, 4 figs, 7 tabs
Li, Yanjun; Tang, Xiaoying; Xu, Zhi; Liu, Weifeng; Li, Jing
2016-03-01
Whether the temporal correlation between inter-leads Electroencephalogram (EEG) that located on the boundary between left and right brain hemispheres is associated with sleep stages or not is still unknown. The purpose of this paper is to evaluate the role of correlation coefficients between EEG leads Fpz-Cz and Pz-Oz for automatic classification of sleep stages. A total number of 39 EEG recordings (about 20 h each) were selected from the expanded sleep database in European data format for temporal correlation analysis. Original waveform of EEG was decomposed into sub-bands δ (1-4 Hz), θ (4-8 Hz), α (8-13 Hz) and β (13-30 Hz). The correlation coefficient between original EEG leads Fpz-Cz and Pz-Oz within frequency band 0.5-30 Hz was defined as r(EEG) and was calculated every 30 s, while that between the two leads EEG in sub-bands δ, θ, α and β were defined as r(δ), r(θ), r(α) and r(β), respectively. Classification of wakefulness and sleep was processed by fixed threshold that derived from the probability density function of correlation coefficients. There was no correlation between EEG leads Fpz-Cz and Pz-Oz during wakefulness (|r| r > 0.1 for r(EEG) and r(δ)), while low correlation existed during sleep (r ≈ -0.4 for r(EEG), r(δ), r(θ), r(α) and r(β)). There were significant differences (analysis of variance, P correlation index between EEG leads Fpz-Cz and Pz-Oz could distinguish all five types of wakefulness, rapid eye movement (REM) sleep, N1 sleep, N2 sleep and N3 sleep. In conclusion, the temporal correlation between EEG bipolar leads Fpz-Cz and Pz-Oz are highly associated with sleep-wake stages. Moreover, high accuracy of sleep-wake classification could be achieved by the temporal correlation within frequency band 0.5-30 Hz between EEG leads Fpz-Cz and Pz-Oz.
Theoretical Studies of Magnetic Systems. Final Report, August 1, 1994 - November 30, 1997
Gor`kov, L. P.; Novotny, M. A.; Schrieffer, J. R.
1997-01-01
During the grant period the authors have studied five areas of research: (1) low dimensional ferrimagnets; (2) lattice effects in the mixed valence problem; (3) spin compensation in the one dimensional Kondo lattice; (4) the interaction of quasi particles in short coherence length superconductors; and (5) novel effects in angle resolved photoemission spectra from nearly antiferromagnetic materials. Progress in each area is summarized.
Energy Technology Data Exchange (ETDEWEB)
Goettel, Stefan
2015-05-22
In this thesis, we study two recently developed methods to tackle low-dimensional correlated quantum systems. In the first part, we benchmark the extension of the functional renormalization group to spin-systems. We apply it to the two-dimensional XXZ model and reproduce the prediction for the phase transition from planar to axial ordering at the isotropic point. The interpretation of the critical scale (where the flow of the susceptibility diverges) as the critical temperature of the system can be questioned, since it yields only good results in the Ising limit. Especially near the isotropic point, this interpretation becomes unsatisfactory as the Mermin-Wagner theorem is violated. We discuss several problems of the method and conclude that it should only be used to explore phase diagrams. In the second part, we extend previous works to two-level quantum dots in the Coulomb blockade regime with special hopping matrices in nonequilibrium, e.g., the Kondo model, to the generic form, including ferromagnetic leads, spin-orbit interactions etc. The dot and the transport observables are determined completely by the hybridization matrix, leading to one of our major results that all these models can be mapped to the Anderson impurity model with ferromagnetic leads. We investigate this model with a well-controlled real-time renormalization group approach and justify the results of a poor man's scaling analysis. By using a singular value decomposition of the tunneling matrix we can rotate the model to the anisotropic Kondo model in the high-energy regime to solve the flow equations analytically. With this, we calculate the stationary dot magnetization and the current. The minimum of the magnetization is found to be an ellipsoid as function of the magnetic field, where the stretching factor determines the distance to the scaling limit. Afterwards, we consider the special case of two external reservoirs and the system being in the scaling limit and discuss the golden
High-field magnetostriction in CeNiSn{sub 1-x}Ge{sub x} (0<=x<=1) strongly correlated systems
Energy Technology Data Exchange (ETDEWEB)
Moral, A. del, E-mail: delmoral@unizar.e [Laboratorio de Magnetismo de Solidos, Departamento de Fisica de Materia Condensada and ICMA, Universidad de Zaragoza and CSIC, 50009 Zaragoza (Spain); Fuente, C. de la [Laboratorio de Magnetismo de Solidos, Departamento de Fisica de Materia Condensada and ICMA, Universidad de Zaragoza and CSIC, 50009 Zaragoza (Spain)
2010-05-15
Magnetization (down to 1.8 K and up to 9 T) and magnetostriction (down to 4.2 K and up to 30 T) measurements have been performed in the series of polycrystalline intermetallics CeNiSn{sub 1-x}Ge{sub x} (0<=x<=1), which show a crossover from Kondo-lattice to fluctuating valence behaviors with x increase. Magnetostriction observed can be denominated as 'colossal' for a paramagnet (up to 0.68% at 150 K and 30 T), with no sign of saturation. Field, H, induced metamagnetic transitions associated to a change in Ce valence are observed. Three kinds of analysis of magnetostriction have been performed to ascertain the magnetostriction origin. At relatively low field and low temperatures these systems follow well the standard theory of magnetostriction (STM), revealing single-ion crystal field and exchange origins, and a determination of the alpha-symmetry microscopic magnetoelastic parameters have been performed. The valence transition is well explained in terms of the interconfigurational model, which needs an extension up to power H{sup 4}. Application of the scaling (thermodynamics corresponding low states) allows the obtainment of the Grueneisen constant, which increases with x. Needed elastic constants measurements are also reported.
Directory of Open Access Journals (Sweden)
Qin Guo-jie
2014-08-01
Full Text Available Sample-time errors can greatly degrade the dynamic range of a time-interleaved sampling system. In this paper, a novel correction technique employing a cubic spline interpolation is proposed for inter-channel sample-time error compensation. The cubic spline interpolation compensation filter is developed in the form of a finite-impulse response (FIR filter structure. The correction method of the interpolation compensation filter coefficients is deduced. A 4GS/s two-channel, time-interleaved ADC prototype system has been implemented to evaluate the performance of the technique. The experimental results showed that the correction technique is effective to attenuate the spurious spurs and improve the dynamic performance of the system.
Li, Dongmei; Guan, Tian; He, Yonghong; He, Qinghua; Zhang, Yilong; Wang, Xiangnan; Shen, Zhiyuan; Yang, Yuxuan; Qiao, Zhen; Ji, Yanhong
2017-12-01
A differential weak measurement system was presented, exhibiting the self-referencing function for biomolecule real time detection as a label-free optical biosensor. We built a Sagnac interferometer, which limited horizontal (H) and vertical (V) polarization to propagating along the common path but in opposite directions to realize weak measurements with two measuring channels installed in two corners of this Sagnac interferometer. By introducing two half wave plates into the system alternately with the two channels to convert between H and V polarization, we obtained a differential measurement for phase delay, which could quantitatively characterize the refractive index change corresponding to the concentration of samples in the channels. With this system, a real time monitor of molecule concentration in the dialysis process was accomplished, demonstrating the function of self-referencing, which is important for optical label-free molecule detection in a complex biological sample solution.
Variational study of fermionic and bosonic systems with non-Gaussian states: Theory and applications
Shi, Tao; Demler, Eugene; Ignacio Cirac, J.
2018-03-01
We present a new variational method for investigating the ground state and out of equilibrium dynamics of quantum many-body bosonic and fermionic systems. Our approach is based on constructing variational wavefunctions which extend Gaussian states by including generalized canonical transformations between the fields. The key advantage of such states compared to simple Gaussian states is presence of non-factorizable correlations and the possibility of describing states with strong entanglement between particles. In contrast to the commonly used canonical transformations, such as the polaron or Lang-Firsov transformations, we allow parameters of the transformations to be time dependent, which extends their regions of applicability. We derive equations of motion for the parameters characterizing the states both in real and imaginary time using the differential structure of the variational manifold. The ground state can be found by following the imaginary time evolution until it converges to a steady state. Collective excitations in the system can be obtained by linearizing the real-time equations of motion in the vicinity of the imaginary time steady-state solution. Our formalism allows us not only to determine the energy spectrum of quasiparticles and their lifetime, but to obtain the complete spectral functions and to explore far out of equilibrium dynamics such as coherent evolution following a quantum quench. We illustrate and benchmark this framework with several examples: a single polaron in the Holstein and Su-Schrieffer-Heeger models, non-equilibrium dynamics in the spin-boson and Kondo models, the superconducting to charge density wave phase transitions in the Holstein model.
Thermal expansion and magnetostriction measurements on PrIr{sub 2}Zn{sub 20}
Energy Technology Data Exchange (ETDEWEB)
Woerl, Andreas; Stingl, Christian; Sakai, Akito; Gegenwart, Philipp [Experimentalphysics VI, Center for Electronic Correlations and Magnetism, University of Augsburg (Germany); Matsumoto, Keisuke T.; Onimaru, Takahiro [Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima (Japan); Takabatake, Toshiro [Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima (Japan); Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima (Japan)
2016-07-01
Strong hybridization between electric quadrupole moments and conduction electrons gives rise to interesting physical phenomena such as new quantum phases and novel metallic properties. Non-fermi-liquid behavior based on the two channel Kondo effect is predicted by theory. PrIr{sub 2}Zn{sub 20} crystallizes in the CeCr{sub 2}Al{sub 20}-type structure, where the Pr{sup 3+} ions are surrounded by the highly symmetric cubic crystal field of 16 Zn atoms. The ground state is the non-magnetic Γ{sub 3} doublet and carries only electric quadrupole and a magnetic octupole moment. At T{sub Q}=0.11 K the electric quadrupole moments order in a antiferroquadrupolar way. A superconducting transition occurs at T{sub c}=0.05 K. The phase transition at T{sub Q}=0.11 K can be suppressed by high magnetic fields parallel to the [100] direction. We investigate the thermal expansion and magnetostriction at low temperatures. By applying high magnetic fields the system is tuned towards a quadrupolar quantum critical point. Furthermore the reaction of the system on breaking the cubic symmetry by compressive stress is explored.
Channel Estimation for Filter Bank Multicarrier Systems in Low SNR Environments
Energy Technology Data Exchange (ETDEWEB)
Driggs, Jonathan; Sibbett, Taylor; Moradiy, Hussein; Farhang-Boroujeny, Behrouz
2017-05-01
Channel estimation techniques are crucial for reliable communications. This paper is concerned with channel estimation in a filter bank multicarrier spread spectrum (FBMCSS) system. We explore two channel estimator options: (i) a method that makes use of a periodic preamble and mimics the channel estimation techniques that are widely used in OFDM-based systems; and (ii) a method that stays within the traditional realm of filter bank signal processing. For the case where the channel noise is white, both methods are analyzed in detail and their performance is compared against their respective Cramer-Rao Lower Bounds (CRLB). Advantages and disadvantages of the two methods under different channel conditions are given to provide insight to the reader as to when one will outperform the other.
Numerical renormalization group method for entanglement negativity at finite temperature
Shim, Jeongmin; Sim, H.-S.; Lee, Seung-Sup B.
2018-04-01
We develop a numerical method to compute the negativity, an entanglement measure for mixed states, between the impurity and the bath in quantum impurity systems at finite temperature. We construct a thermal density matrix by using the numerical renormalization group (NRG), and evaluate the negativity by implementing the NRG approximation that reduces computational cost exponentially. We apply the method to the single-impurity Kondo model and the single-impurity Anderson model. In the Kondo model, the negativity exhibits a power-law scaling at temperature much lower than the Kondo temperature and a sudden death at high temperature. In the Anderson model, the charge fluctuation of the impurity contributes to the negativity even at zero temperature when the on-site Coulomb repulsion of the impurity is finite, while at low temperature the negativity between the impurity spin and the bath exhibits the same power-law scaling behavior as in the Kondo model.
Magnetic impurity coupled to interacting conduction electrons
International Nuclear Information System (INIS)
Schork, T.
1996-01-01
We consider a magnetic impurity which interacts by hybridization with a system of weakly correlated electrons and determine the energy of the ground state by means of a 1/N f expansion. The correlations among the conduction electrons are described by a Hubbard Hamiltonian and are treated to the lowest order in the interaction strength. We find that their effect on the Kondo temperature, T K , in the Kondo limit is twofold: first, the position of the impurity level is shifted due to the reduction of charge fluctuations, which reduces T K . Secondly, the bare Kondo exchange coupling is enhanced as spin fluctuations are enlarged. In total, T K increases. Both corrections require intermediate states beyond the standard Varma-Yafet ansatz. This shows that the Hubbard interaction does not just provide quasiparticles, which hybridize with the impurity, but also renormalizes the Kondo coupling. copyright 1996 The American Physical Society
Interleaved numerical renormalization group as an efficient multiband impurity solver
Stadler, K. M.; Mitchell, A. K.; von Delft, J.; Weichselbaum, A.
2016-06-01
Quantum impurity problems can be solved using the numerical renormalization group (NRG), which involves discretizing the free conduction electron system and mapping to a "Wilson chain." It was shown recently that Wilson chains for different electronic species can be interleaved by use of a modified discretization, dramatically increasing the numerical efficiency of the RG scheme [Phys. Rev. B 89, 121105(R) (2014), 10.1103/PhysRevB.89.121105]. Here we systematically examine the accuracy and efficiency of the "interleaved" NRG (iNRG) method in the context of the single impurity Anderson model, the two-channel Kondo model, and a three-channel Anderson-Hund model. The performance of iNRG is explicitly compared with "standard" NRG (sNRG): when the average number of states kept per iteration is the same in both calculations, the accuracy of iNRG is equivalent to that of sNRG but the computational costs are significantly lower in iNRG when the same symmetries are exploited. Although iNRG weakly breaks SU(N ) channel symmetry (if present), both accuracy and numerical cost are entirely competitive with sNRG exploiting full symmetries. iNRG is therefore shown to be a viable and technically simple alternative to sNRG for high-symmetry models. Moreover, iNRG can be used to solve a range of lower-symmetry multiband problems that are inaccessible to sNRG.
Quadrupolar order, hidden octupolar order and tiny magnetic moment in URu2Si2
International Nuclear Information System (INIS)
Tsuruta, Atsushi; Matsuura, Tamifusa; Kuroda, Yoshihiro
2000-01-01
Possible orders in URu 2 Si 2 are investigated using a two-channel degenerate Anderson model. The ground state of uranium ions is the non-Kramers quadrupolar doublet Γ 5 with (5f) 2 , and its relevant excited state is the Kramers dipolar doublet Γ 7 with (5f) 1 . These states mix with each other via conduction electrons. At low temperatures, the system forms renormalized bands with both quadrupole and dipole degrees of freedom due to the quadrupolar Kondo effect which slightly mixes quadrupolar Γ 5 , a primary state of uranium ions, with dipolar Γ 7 . At a certain low temperature, conduction electrons in the renormalized bands undergo quadrupolar ordering with a large quadrupolar moment. At a further lower temperature, octupolar ordering occurs, accompanied by a tiny dipolar moment which is attributed to the property of the renormalized bands with primarily the Γ 5 -character slightly mixed with the Γ 7 -character. These phenomena are well described by the 1/N-expansion method with pseudo-fermions for the non-Kramers doublet Γ 5 and slave bosons for the Kramers doublet Γ 7 . (author)
Equilibrium charge fluctuations of a charge detector and its effect on a nearby quantum dot
Ruiz-Tijerina, David; Vernek, Edson; Ulloa, Sergio
2014-03-01
We study the Kondo state of a spin-1/2 quantum dot (QD), in close proximity to a quantum point contact (QPC) charge detector near the conductance regime of the 0.7 anomaly. The electrostatic coupling between the QD and QPC introduces a remote gate on the QD level, which varies with the QPC gate voltage. Furthermore, models for the 0.7 anomaly [Y. Meir et al., PRL 89,196802(2002)] suggest that the QPC lodges a Kondo-screened level with charge-correlated hybridization, which may be also affected by capacitive coupling to the QD, giving rise to a competition between the two Kondo ground states. We model the QD-QPC system as two capacitively-coupled Kondo impurities, and explore the zero-bias transport of both the QD and the QPC for different local gate voltages and coupling strengths, using the numerical renormalization group and variational methods. We find that the capacitive coupling produces a remote gating effect, non-monotonic in the gate voltages, which reduces the gate voltage window for Kondo screening in either impurity, and which can also drive a quantum phase transition out of the Kondo regime. Our study is carried out for intermediate coupling strengths, and as such is highly relevant to experiments; particularly, to recent studies of decoherence effects on QDs. Supported by MWN/CIAM and NSF PIRE.
Energy Technology Data Exchange (ETDEWEB)
Sykora, Steffen [IFW Dresden, P.O. Box 270116, D-01171 Dresden (Germany); Becker, Klaus W. [Technische Universitaet Dresden, D-01062 Dresden (Germany)
2016-07-01
In this paper we discuss a new phase of the Kondo lattice model which arises from the competition of Kondo and RKKY energy scales. Normally the Kondo lattice model is used to capture the low-energy physics of heavy fermion systems. However, according to the so-called Doniach picture the Kondo state will be replaced by an antiferromagnetic state for the case that the Kondo energy scale becomes smaller than the magnetic interaction between magnetic ions. In the present study we start instead from a modified electronic one-particle dispersion which avoids nesting of particle-hole excitations. Thus the magnetic ordered state should be suppressed which provides an opportunity for the inset of a new low-energy state with competing Kondo and magnetic energies. As will be shown, this new state avoids magnetic symmetry breaking but leads to a number of physical properties which are relevant for the understanding of the hidden order state in URu{sub 2}Si{sub 2}.
Cross-talk dynamics of optical solitons in a broadband Kerr nonlinear system with weak cubic loss
International Nuclear Information System (INIS)
Peleg, Avner; Nguyen, Quan M.; Chung, Yeojin
2010-01-01
We study the dynamics of fast soliton collisions in a Kerr nonlinear optical waveguide with weak cubic loss. We obtain analytic expressions for the amplitude and frequency shifts in a single two-soliton collision and show that the impact of a fast three-soliton collision is given by the sum of the two-soliton interactions. Our analytic predictions are confirmed by numerical simulations with the perturbed nonlinear Schroedinger (NLS) equation. Furthermore, we show that the deterministic collision-induced dynamics of soliton amplitudes in a broadband waveguide system with N frequency channels is described by a Lotka-Volterra model for N competing species. For a two-channel system we find that stable transmission with equal prescribed amplitudes can be achieved by a proper choice of linear amplifier gain. The predictions of the Lotka-Volterra model are confirmed by numerical solution of a perturbed coupled-NLS model.
Ground state and elementary excitations of a model valence-fluctuation system
International Nuclear Information System (INIS)
Brandow, B.H.
1979-01-01
The nature of the valence fluctuation problem is described, and motivations are given for an Anderson-lattice model Hamiltonian. A simple trial wave function is posed for the ground state, and the variational problem is solved. This demonstrates clearly that there is no Kondo-like divergence; the present concentrated Kondo problem is thus more simple mathematically than the sngle-impurity problem. Elementary excitations are studies by the Green's function techniques of Zubarev and Hubbard. Quenching of local moments and a large specific heat are found at low temperatures. The quasi-particle spectrum exhibits a gap, but epsilon/sub F/ does not lie in this gap. The insulation-like feature of SmB 6 , SmS, and TmSe at very low temperatures is explained in terms of a strongly reduced mobility for states near the gap, and reasons are given why this feature is not observed in other valence-fluctuation compounds. 73 references
International Nuclear Information System (INIS)
Stinshoff, H.
2003-01-01
To improve the reliability of Kozloduy Nuclear power plant several modernization measures will be implemented during the outages in the years 2003 to 2005. In the area of the main generator the following measures will be performed in unit 6 during 2003 outage: - Replacement of main generator circuit breaker by new SF6 cooled breaker type - Replacement of main generator excitation system by new two channel digital system - Replacement of main generator protection by new digital multi-purpose protections including digital fault recorders - Installation of radio frequency monitoring system of main generator circuit Starting from the present situation the new concept is explained. The project organization under consideration of large Bulgarian participation as well as the sequence and schedule of the implementation during the short outage time window is shown. These modernization measures lead to an increase of reliability and availability for the operation of the power plant and with this to increase power plant safety
Universality class of non-Fermi liquid behaviour in mixed valence systems
International Nuclear Information System (INIS)
Zhang Guangming; Su Zhaobin; Lu Yu
1995-11-01
A generalized Anderson single-impurity model with off-site Coulomb interactions is derived from the extended three-band Hubbard model, originally proposed to describe the physics of the copper-oxides. Using the abelian bosonization technique and canonical transformations, an effective Hamiltonian is derived in the strong coupling limit, which is essentially analogous to the Toulouse limit of the ordinary Kondo problem. In this limit, the effective Hamiltonian can be exactly solved, with a mixed valence quantum critical point separating two different Fermi liquid phases, i.e. the Kondo phase and the empty orbital phase. In the mixed valence quantum critical regime, the local moment is only partially quenched and X-ray edge singularities are generated. Around the quantum critical point, a new type of non-Fermi liquid behaviour is predicted with an extra specific heat C imp ∼ T 1/4 and a singular spin-susceptibility χ imp ∼ T -3/4 . At the same time, the effective Hamiltonian under single occupancy is transformed into a resonant-level model, from which the correct Kondo physical properties (specific heat, spin susceptibility, and an enhanced Wilson ratio) are easily rederived. Finally, a brief discussion is given to relate these theoretical results to observations in U Pd x Cu 5-x (x=1, 1.5) alloys, which show single-impurity critical behaviour consistent with our predictions. (author). 30 refs
Universality class of non-Fermi-liquid behavior in mixed-valence systems
Zhang, Guang-Ming; Su, Zhao-Bin; Yu, Lu
1996-01-01
A generalized Anderson single-impurity model with off-site Coulomb interactions is derived from the extended three-band Hubbard model, originally proposed to describe the physics of the copper oxides. Using the Abelian bosonization technique and canonical transformations, an effective Hamiltonian is derived in the strong-coupling limit, which is essentially analogous to the Toulouse limit of the ordinary Kondo problem. In this limit, the effective Hamiltonian can be exactly solved, with a mixed-valence quantum critical point separating two different Fermi-liquid phases, i.e., the Kondo phase and the empty orbital phase. In the mixed-valence quantum critical regime, the local moment is only partially quenched and x-ray edge singularities are generated. Around the quantum critical point, a type of non-Fermi-liquid behavior is predicted with an extra specific heat Cimp~T1/4 and a singular spin susceptibility χimp~T-3/4. At the same time, the effective Hamiltonian under single occupancy is transformed into a resonant-level model, from which the correct Kondo physical properties (specific heat, spin susceptibility, and an enhanced Wilson ratio) are easily rederived. Finally, a brief discussion is given to relate these theoretical results to observations in UPdxCu5-x (x=1,1.5) alloys, which show single-impurity critical behavior consistent with our predictions.
Godisov, O N; Yudkin, M I; Gerasimov, S F; Feofilov, G A
1994-01-01
Contradictory demands raised by the application of different types of sensitive detectors in 5 layers of the Inner Tracking System (ITS) for ALICE stipulate the simultaneous use of different schemes of heat drain: gaseous cooling of the 1st layer (uniform heat production over the sensitive surface) and evaporative cooling for the 2nd-5th layers (localised heat production). The last system is also a must for the thermostabilization of Si-drift detectors within 0.1 degree C. Theoretical estimates of gaseous, evaporative and liquid cooling systems are done for all ITS layers. The results of the experiments done for evaporative and liquid heat drain systems are presented and discussed. The major technical problems of the evaporative systems' design are being considered: i) control of liquid supply; ii) vapour pressure control. Two concepts of the evaporative systems are proposed: 1) One channel system for joint transfer of two phases (liquid + gas); 2) Two channels system with separate transfer of phases. Both sy...
van Stam, Gerard; Kok, H Petra; Hulshof, Maarten C C M; Kolff, M Willemijn; van Tienhoven, Geertjan; Sijbrands, Jan; Bakker, Akke; Zum Vörde Sive Vörding, Paul J; Oldenborg, Sabine; de Greef, Martijn; Rasch, Coen R N; Crezee, Hans
2017-11-01
Superficial tumours with deep infiltration in the upper 15 cm of the trunk cannot be treated adequately with existing hyperthermia systems. The aim of this study was to develop, characterise and evaluate a new flexible two-channel hyperthermia system (AMC-2) for tumours in this region. The two-channel AMC-2 system has two horizontally revolving and height adjustable 70 MHz waveguides. Three different interchangeable antennas with sizes 20 × 34, 15 × 34 and 8.5 × 34 cm were developed and their electrical properties were determined. The performance of the AMC-2 system was tested by measurements of the electric field distribution in a saline water filled elliptical phantom, using an electric field vector probe. Clinical feasibility was demonstrated by treatment of a melanoma in the axillary region. Phantom measurements showed a good performance for all waveguides. The large reflection of the smallest antenna has to be compensated by increased forward power. Field patterns become asymmetrical when using smaller top antennas, necessitating phase corrections. The clinical application showed that tumours deeper than 4 cm can be heated adequately. A median tumour temperature of 42 °C can be reached up to 12 cm depth with adequate antenna positioning and phase-amplitude steering. This 70 MHz AMC-2 waveguide system is a useful addition to existing loco-regional hyperthermia equipment as it is capable of heating axillary tumours and other tumours deeper than 4 cm.
Energy Technology Data Exchange (ETDEWEB)
Kawamori, Eiichirou; Lin, Yu-Hsiang [Institute of Space and Plasma Sciences, National Cheng Kung University, Tainan 70101, Taiwan (China); Mase, Atsushi [Art, Science and Technology Center for Cooperative Research, Kyushu University, Kasuga 816-8580 (Japan); Nishida, Yasushi; Cheng, C. Z. [Institute of Space and Plasma Sciences, National Cheng Kung University, Tainan 70101, Taiwan (China); Plasma and Space Science Center, National Cheng Kung University, Tainan 70101, Taiwan (China)
2014-02-15
This study presents a simple and powerful technique for multichannel measurements of the density profile in laboratory plasmas by microwave interferometry. This technique uses electromechanical microwave switches to temporally switch the connection between multiple receiver antennas and one phase-detection circuit. Using this method, the phase information detected at different positions is rearranged into a time series that can be acquired from a minimum number of data acquisition channels (e.g., two channels in the case of quadrature detection). Our successfully developed multichannel microwave interferometer that uses the antenna switching method was applied to measure the radial electron density profiles in a magnetized plasma experiment. The advantage of the proposed method is its compactness and scalability to multidimensional measurement systems at low cost.
Spin-glass, antiferromagnetism and Kondo behavior in Ce 2 Au 1- ...
Indian Academy of Sciences (India)
) and magnetoresistance of various alloys of this solid solution in order to gain better knowledge of the magnetism of these alloys. High pressure resistivity behavior is consistent with the proposal that Ce2AuSi3 lies at the left-hand side of the ...
Spin gap and antiferromagnetic correlations in the kondo insulator CeNiSn
DEFF Research Database (Denmark)
Mason, T.E.; Aeppli, G.; Ramirez, A.P.
1992-01-01
Neutron scattering measurements show that the crossover (at T less than or similar to 10 K) from metallic heavy-fermion to semiconducting behavior coincides with the formation of a gap in the magnetic excitation spectrum of CeNiSn. In contrast to the simple band picture of an insulator, the gap...... is well defined only at particular values of the momentum transfer Q. While substantial antiferromagnetic correlations in the a-c plane characterize the low-T state, the corresponding zero-frequency response function is Q independent....
From Kondo model and strong coupling lattice QCD to the Isgur-Wise function
International Nuclear Information System (INIS)
Patel, Apoorva
1995-01-01
Isgur-Wise functions parametrise the leading behaviour of weak decay form factors of mesons and baryons containing a single heavy quark. The form factors for the quark mass operator are calculated in strong coupling lattice QCD, and Isgur-Wise functions extracted from them. Based on renormalisation group invariance of the operators involved, it is argued that the Isgur-Wise functions would be the same in the weak coupling continuum theory. (author)
The Kondo problem. II. Crossover from asymptotic freedom to infrared slavery
Schlottmann, P.
1982-04-01
In the preceding paper we transformed the s-d Hamiltonian onto a resonance level with a large perturbation and derived the scaling equations for the vertices, the invariant coupling, and the resonance width. The scaling equations are integrated under the assumption that the energy dependence of the resonance width can be neglected. The transcendental equation obtained in this way for the renormalized resonance width is solved in the relevant limits and allows a calculation of the static and dynamical susceptibility. At high temperatures the perturbation expansion for the relaxation rate and the susceptibility is reproduced up to third order in Jρ. At low temperatures the lifetime and χ0 remain finite and vary according to a Fermi-liquid theory. The approximation scheme interpolates in this way between the asymptotic freedom and the infrared slavery, yielding a smooth crossover. The present results are in quantitative agreement with previous ones obtained with the relaxation-kernel method by Götze and Schlottmann. The advantages and drawbacks of the method are discussed. The calculation of the dynamical susceptibility is extended to nonzero external magnetic fields. The quasielastic peak of χ''(ω)ω is suppressed at low temperatures and large magnetic fields and shoulders develop at ω=+/-B.
TQUID Magnetometer and Artificial Neural Circuitry Based on a Topological Kondo Insulator
2016-05-01
samples are leached out in sodium hydroxide solution. The surfaces of these crystals were carefully etched using an equal mixture of hydrochloric acid...Dopants using EDS Left: EDS data of a 3% Ce doped SmB6 sample and right: SEM image of the sample (with 4 gold wires for transport measurements
Polarized-neutron study of spin dynamics in the Kondo insulator YbB12.
Nemkovski, K S; Mignot, J-M; Alekseev, P A; Ivanov, A S; Nefeodova, E V; Rybina, A V; Regnault, L-P; Iga, F; Takabatake, T
2007-09-28
Inelastic neutron scattering experiments have been performed on the archetype compound YbB(12), using neutron polarization analysis to separate the magnetic signal from the phonon background. With decreasing temperature, components characteristic for a single-site spin-fluctuation dynamics are suppressed, giving place to specific, strongly Q-dependent, low-energy excitations near the spin-gap edge. This crossover is discussed in terms of a simple crystal-field description of the incoherent high-temperature state and a predominantly local mechanism for the formation of the low-temperature singlet ground state.
Leading temperature dependence of the conductance in Kondo-correlated quantum dots
Aligia, A. A.
2018-04-01
Using renormalized perturbation theory in the Coulomb repulsion, we derive an analytical expression for the leading term in the temperature dependence of the conductance through a quantum dot described by the impurity Anderson model, in terms of the renormalized parameters of the model. Taking these parameters from the literature, we compare the results with published ones calculated using the numerical renormalization group obtaining a very good agreement. The approach is superior to alternative perturbative treatments. We compare in particular to the results of a simple interpolative perturbation approach.
A Multi-Layer Phoswich Radioxenon Detection System
International Nuclear Information System (INIS)
David M. Hamby
2007-01-01
Further work was performed in optical modeling of the modified (dual planar) XEPHWICH design. Modeling capabilities and understanding were expanded through the performance of three additional simulations. The efficiency of the entire optical modeling process was increased by developing custom software to interface with both the input and output of the simulation program. Work continues on the design and implementation of the analog portion of the read-out system. This component is being prototyped and is nearing completion. The PCB (printed circuit board) is in its design phase for the two-channel digital pulse processor, necessary for the dual planar XEPHWICH. System components are being selected for the signal processor based on a balance of cost and our expectations of quality. Outside the scope of the grant, but entirely related, we continue to work on developing a source of fission-product xenon gases that will be produced in the OSU TRIGA reactor. The amount of HEU necessary to provide the needed activities of xenon fission products, as well as build-in times for each isotope of importance following irradiation, have been calculated. Irradiation times in the TRIGA have been determined. We've finalized our design of the xenon-fission-product collection chamber and initiated in-house fabrication. PNNL will be supplying the thin foils of enriched uranium necessary for xenon production
Non-Fermi liquid scaling in UPdxCu5-x(x = 1,1.5)
International Nuclear Information System (INIS)
Aronson, M.C.; Osborn, R.; Lynn, J.W.; Chau, R.; Seaman, C.L.; Maple, M.B.
1994-08-01
The family of uranium based intermetallics UPd x Cu 5-x offers an ideal isostructural system to study the interplay of the impurity Kondo effect with the stability of long range magnetic order in a Kondo lattice. The parent compound UCu 5 is a prototypical Kondo impurity system at high temperatures, with Kondo temperature T K ∼ 5--10 meV. As the temperature is lowered, intersite interactions drive a transition to long-range antiferromagnetic order of the incompletely compensated uranium moments at 15 K. As Pd is substituted on the Cu sites, the antiferromagnetism is suppressed, with the ordering temperature driven to zero slightly below the composition UPdCu 4 . Unusual temperature and magnetic field scaling is observed in the magnetization, specific heat, and electrical resistivity of both UPdCu 4 and UPd 1.5 Cu 3.5 , inconsistent with the Fermi liquid description appropriate for many Kondo lattice systems, and in particular the parent compound UCu 5 . The authors report here the first direct measurements of the fundamental magnetic response for both compounds, providing a clear demonstration of non-Fermi liquid frequency and temperature scaling
DiFranco, Marino; Quinonez, Marbella
2012-01-01
A two-microelectrode voltage clamp and optical measurements of membrane potential changes at the transverse tubular system (TTS) were used to characterize delayed rectifier K currents (IKV) in murine muscle fibers stained with the potentiometric dye di-8-ANEPPS. In intact fibers, IKV displays the canonical hallmarks of KV channels: voltage-dependent delayed activation and decay in time. The voltage dependence of the peak conductance (gKV) was only accounted for by double Boltzmann fits, suggesting at least two channel contributions to IKV. Osmotically treated fibers showed significant disconnection of the TTS and displayed smaller IKV, but with similar voltage dependence and time decays to intact fibers. This suggests that inactivation may be responsible for most of the decay in IKV records. A two-channel model that faithfully simulates IKV records in osmotically treated fibers comprises a low threshold and steeply voltage-dependent channel (channel A), which contributes ∼31% of gKV, and a more abundant high threshold channel (channel B), with shallower voltage dependence. Significant expression of the IKV1.4 and IKV3.4 channels was demonstrated by immunoblotting. Rectangular depolarizing pulses elicited step-like di-8-ANEPPS transients in intact fibers rendered electrically passive. In contrast, activation of IKV resulted in time- and voltage-dependent attenuations in optical transients that coincided in time with the peaks of IKV records. Normalized peak attenuations showed the same voltage dependence as peak IKV plots. A radial cable model including channels A and B and K diffusion in the TTS was used to simulate IKV and average TTS voltage changes. Model predictions and experimental data were compared to determine what fraction of gKV in the TTS accounted simultaneously for the electrical and optical data. Best predictions suggest that KV channels are approximately equally distributed in the sarcolemma and TTS membranes; under these conditions, >70% of IKV
Atkinson, Matthew; Chukwumah, Chike; Marks, Jeffrey; Chak, Amitabh
2014-02-01
Flat and depressed lesions are becoming increasingly recognized in the esophagus, stomach, and colon. Various techniques have been described for endoscopic mucosal resection (EMR) of these lesions. To evaluate the efficacy of lift-grasp-cut EMR using a prototype dual-channel forward-viewing endoscope with an instrument elevator in one accessory channel (dual-channel elevator scope) as compared to standard dual-channel endoscopes. EMR was performed using a lift-grasp-cut technique on normal flat rectosigmoid or gastric mucosa in live porcine models after submucosal injection of 4 mL of saline using a dual-channel elevator scope or a standard dual-channel endoscope. With the dual-channel elevator scope, the elevator was used to attain further lifting of the mucosa. The primary endpoint was size of the EMR specimen and the secondary endpoint was number of complications. Twelve experiments were performed (six gastric and six colonic). Mean specimen diameter was 2.27 cm with the dual-channel elevator scope and 1.34 cm with the dual-channel endoscope (P = 0.018). Two colonic perforations occurred with the dual-channel endoscope, vs no complications with the dual-channel elevator scope. The increased lift of the mucosal epithelium, through use of the dual-channel elevator scope, allows for larger EMR when using a lift-grasp-cut technique. Noting the thin nature of the porcine colonic wall, use of the elevator may also make this technique safer.
Energy Technology Data Exchange (ETDEWEB)
Studenikin, S. A.; Gaudreau, L.; Kataoka, K.; Austing, D. G.; Lu, Tzu-Ming; Luhman, Dwight; Bethke, Donald Thomas; Wanke, Michael; Lilly, Michael; Carroll, Malcolm S.; Sachrajda, A. S.
2017-12-01
We demonstrate coupled triple dot operation and charge sensing capability for the recently introduced quantum dot technology employing undoped Si/Si_{0.8}Ge_{0.2} hetero-structures which also incorporate a single metal-gate layer to simplify fabrication [T. M. Lu et al., Appl. Phys. Lett. 109, 093102 (2016)]. Si/SiGe hetero-structures with a Ge concentration of 20% rather than the more usual 30% typically encountered offer higher electron mobility. The devices consist of two in-plane parallel electron channels that host a double dot in one channel and a single dot in the other channel. In a device where the channels are sufficiently close a triple dot in a triangular configuration is induced leading to regions in the charge stability diagram where three addition lines of different slope approach each other and anti-cross. In a device where the channels are further apart the single dot charge-senses the double dot with relative change of ~2% in the sensor current. We also highlight temporal drifting and metastability of the Coulomb oscillations. These effects are induced if the temperature environment of the device is not kept constant and arise from non-equilibrium charge redistribution and subsequent slow recovery.
DEFF Research Database (Denmark)
Jeppesen, Palle
1996-01-01
The lecture note is aimed at introducing system budgets for optical communication systems. It treats optical fiber communication systems (six generations), system design, bandwidth effects, other system impairments and optical amplifiers.......The lecture note is aimed at introducing system budgets for optical communication systems. It treats optical fiber communication systems (six generations), system design, bandwidth effects, other system impairments and optical amplifiers....
Study of flow instabilities in double-channel natural circulation boiling systems
International Nuclear Information System (INIS)
Durga Prasad, Gonella V.; Pandey, Manmohan; Pradhan, Santosh K.; Gupta, Satish K.
2008-01-01
Natural circulation boiling systems consisting of parallel channels can undergo different types of oscillations (in-phase or out-of-phase) depending on the geometric parameters and operating conditions. Disturbances in one channel affect the flow in other channels, which triggers thermal-hydraulic oscillations. In the present work, the modes of oscillation under different operating conditions and channel-to-channel interaction during power fluctuations and on-power refueling in a double-channel natural circulation boiling system are investigated. The system is modeled using a lumped parameter mathematical model and RELAP5/MOD3.4. Parametric studies are carried out for an equal-power double-channel system, at different operating conditions, with both the models, and the results are compared. Instabilities, non-linear oscillations, and effects of recirculation loop dynamics and geometric parameters on the mode of oscillations, are studied using the lumped model. The two channels oscillate out-of-phase in Type-I region, but in Type-II region, both the modes of oscillation are observed under different conditions. Channel-to-channel interaction and on-power refueling studies are carried out using the RELAP model. At high powers, disturbances in one channel significantly affect the stability of the other channel. During on-power refueling, a near-stagnation condition or low-velocity reverse flow can occur, the possibility of reverse flow being higher at lower pressures
Comparison of control systems applied to the handling of radioactive reactor components
International Nuclear Information System (INIS)
Robinson, C.; Harris, E.G.; Dyer, P.C.; Williams, J.G.B.
1985-01-01
The first generation of nuclear power stations have individual reactors each incorporating complete facilities for servicing components and refuelling. In the later designs, each power station has two reactors which are connected by a central block. This central block contains one set of facilities to service both reactors, but to improve the station capability, some of these are to be replicated. The central block incorporates a hoist well which was used during construction for the accessing of complete components. On completion of this work, the physical size of the hoist well is such as to permit the incorporation of additional facilities if these are shown to be operationally and economically desirable. Since a number of years of power operation has elapsed, the advantages of back-fitting to existing fuel-handling facilities has been illustrated. Since the mechanical arrangements and operating procedures are substantially similar for both the original and new handling facilities, the paper will illustrate the control systems provided for each. The configuration of the system is arranged to have two channels of control which complies with the current standard requirements in the United Kingdom. These requirements are more stringent than when the existing facility was designed and constructed, as described in the relevant sections of the paper. The new system has been designed and is being manufactured to comply with the Central Electricity Generating Board standard for nuclear fuel route interlock and control systems. (author)
A microcontroller-based telemetry system for sympathetic nerve activity and ECG measurement.
Harada, E; Yonezawa, Y; Caldwell, W M; Hahn, A W
1999-01-01
A telemetry system employing a low power 8-bit microcontroller has been developed for chronic unanesthetized small animal studies. The two-channel system is designed for use with animals in shielded cages. Analog signals from implantable ECG and nerve electrodes are converted to an 8-bit serial digital format. This is accomplished by individual 8 bit A/D converters included in the microcontroller, which also has serial I/O port. The converted serial binary code is applied directly to an antenna wire. Therefore, the system does not need to employ a separate transmitter, such as in FM or infrared optical telemeters. The system is used in a shielded animal cage to reduce interference from external radio signals and 60 Hz power line fields. The code is received by a high input impedance amplifier in the cage and is then demodulated. The telemeter is powered by a small 3 V lithium battery, which provides 100 hours of continuous operation. The circuit is constructed on two 25 x 25 mm. printed circuit boards and encapsulated in epoxy, yielding a total volume of 6.25 cc. The weight is 15 g.
Superconductivity and magnetism: From antagonism to mutual interplay
International Nuclear Information System (INIS)
Steglich, Frank
2007-01-01
In this paper, a brief survey is given on a number of research activities devoted to exploring the relationship between superconductivity and magnetism in f-electron systems. The starting point for these activities has been the pioneering work of 1958 by Matthias and coworkers illustrating the antagonistic nature of the two phenomena. Subsequent efforts concerned the investigation of Kondo superconductors and Kondo-lattice systems (in the 1970s), heavy-fermion metals (in the 1980s and 90s) and quantum critical materials (in the last decade). The latter systems are especially interesting as they promise a deeper insight into the mutual interplay between unconventional superconductivity and magnetism
Analysis of flow distribution instability in parallel thin rectangular multi-channel system
Energy Technology Data Exchange (ETDEWEB)
Xia, G.L. [School of Nuclear Science and Technology, Xi’an Jiaotong University, Xi’an City 710049 (China); Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, Harbin Engineering University, Harbin City 150001 (China); Su, G.H., E-mail: ghsu@mail.xjtu.edu.cn [School of Nuclear Science and Technology, Xi’an Jiaotong University, Xi’an City 710049 (China); Peng, M.J. [Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, Harbin Engineering University, Harbin City 150001 (China)
2016-08-15
Highlights: • Flow distribution instability in parallel thin rectangular multi-channel system is studied using RELAP5 codes. • Flow excursion may bring parallel heating channel into the density wave oscillations region. • Flow distribution instability is more likely to happen at low power/flow ratio conditions. • The increase of channel number will not affect the flow distribution instability boundary. • Asymmetry inlet throttling and heating will make system more unstable. - Abstract: The flow distribution instability in parallel thin rectangular multi-channel system has been researched in the present study. The research model of parallel channel system is established by using RELAP5/MOD3.4 codes. The transient process of flow distribution instability is studied at imposed inlet mass flow rate and imposed pressure drop conditions. The influence of heating power, mass flow rate, system pressure and channel number on flow distribution instability are analyzed. Furthermore, the flow distribution instability of parallel two-channel system under asymmetric inlet throttling and heating power is studied. The results show that, if multi-channel system operates at the negative slope region of channel ΔP–G curve, small disturbance in pressure drop will lead to flow redistribution between parallel channels. Flow excursion may bring the operating point of heating channel into the density-wave oscillations region, this will result in out-phase or in-phase flow oscillations. Flow distribution instability is more likely to happen at low power/flow ratio conditions, the stability of parallel channel system increases with system pressure, the channel number has a little effect on system stability, but the asymmetry inlet throttling or heating power will make the system more unstable.
Directory of Open Access Journals (Sweden)
Gianluca Brando
2016-09-01
Full Text Available In the context of grid connected photovoitaic (PV generation systems, there are two paramount aspects regarding the Maximum Power Point Tracking (MPPT of the photovoltaic units and the continuity of the service. The most diffused MPPT algorithms are based on either perturb and observe, or on an incremental conductance approach and need both PV current and voltage measurements. Several topology reconfigurable converters are also associated with the PV plants, guaranteeing fault-tolerant features. The generation continuity can also be assured by interleaved inverters, which keep the system operating at reduced maximum power in case of failure. In this paper, an evolution of a hysteresis based MPPT algorithm is presented, based on the measurement of only one voltage, together with a novel space vector modulation suitable for a two-channel three-phase grid connected interleaved inverter. The proposed MMPT algorithm and modulation technique are tested by means of several numerical analyses on a PV generation system of about 200 kW maximum power. The results testify the validity of the proposed strategies, showing good performance, even during a fault occurrence and in the presence of deep shading conditions.
Multi-channel data acquisition and processing system for moessbauer spectroscopy
International Nuclear Information System (INIS)
Jin Ge; Yang Yanming
1987-01-01
A multi-channel data acquisition and processing system for moessbauer spectroscopy is described, which consists of an intelligent interface and a BC3-80 microcomputer. The system has eight data channels, each channel contains a counting circuit and a memory. A Z80-CPU is used as a main unit for control and access. The microcomputer is used for real-time displaying spectrum, saving the data to disk, printing data and data processing. The system is applicable to a high counting rate multi-wire proportional chamber. It can increase greatly the counting rate for measuring moessbauer spectrum. The signals of each wire in the chamber go through a corresponding amplifier and a differential discriminator and are recorded by a corresponding data channel, the data of each channel is added by the microcomputer. In addition, two channels can be used to measure an absorption and a scattering spectrum at the same time and the internal and the surface information of the sample are obtained simultaneously
International Nuclear Information System (INIS)
Gossler
1980-01-01
The present paper deals with - controlled area ventilation systems - ventilation systems for switchgear-building and control-room - other ventilation systems for safety equipments - service systems for ventilation systems. (orig./RW)
Spin fluctuation effects on the conductance through a single Pd atom contact
International Nuclear Information System (INIS)
Romero, M A; Goldberg, E C; Gomez-Carrillo, S C; Bolcatto, P G
2009-01-01
A controversy about the conductance through single atoms still exists. There are many experiments where values lower than the quantum unity G 0 = 2e 2 /h have been found associated to Kondo regimes with high Kondo temperatures. Specifically in the Pd single atom contact, conductance values close to G 0 /2 at room temperature have been reported. In this work we propose a theoretical analysis of a break junction of Pd where the charge fluctuation in the single atom contact is limited to the most probable one: d 10 ↔d 9 . The projected density of states and the characteristics of the electron transport are calculated by using a realistic description of the interacting system. A Kondo regime is found where the conductance values and their dependence on temperature are in good agreement with the experimental trends observed in the conduction of single molecule transistors based on transition metal coordination complexes.
Origin of the -|A | T1 /2 term in the resistivity of disordered ZrAs1.58Se0.39
Gnida, Daniel
2018-04-01
Recently, Cichorek et al. have analyzed the magnetic-field-independent -|A | T1 /2 term in the resistivity of disordered ZrAs1.58Se0.39 within the Altshuler-Arononv model of electron-electron interaction in the presence of disorder [Phys. Rev. Lett. 117, 106601 (2016), 10.1103/PhysRevLett.117.106601]. Making the assumption that diffusion of conduction electrons in this compound is isotropic, they could not get quantitative agreement between the considered model and the experimental results. This led the authors to conclude that the singular T1 /2 contribution to the resistivity of ZrAs1.58Se0.39 could not be caused by electron-electron interaction but could only be explained by a two-channel Kondo effect. Here, we perform a detailed analysis of the -|A | T1 /2 correction to the resistivity of disordered ZrAs1.58Se0.39 using analogous Altshuler-Aronov relation but taking into account that the diffusion coefficient in the tetragonal ZrAs1.58Se0.39 is anisotropic. For the considered resistivity anisotropy, we found that the calculated values of the A coefficient are in very good agreement with those derived from the resistivity measurements. Moreover, analysis indicates that the values of the screening parameter λ(j =1 ) are close to zero, which satisfies the condition that the A coefficient does not depend on magnetic field. This shows that the magnetic-field-independent -|A | T1 /2 correction to the resistivity of disordered ZrAs1.58Se0.39 can be explained within the electron-electron interaction scenario in disordered metallic systems.
International Nuclear Information System (INIS)
Pechev, St.
1998-01-01
Three novel phases, U 3 Cu 4 Si 4 , U 3 Cu 4 Ge 4 and UCuGe 1,77 , were prepared in the U - Cu - X (X = Si or Ge) ternary system. Their structural and magnetic properties were investigated. The magnetic structures of the first two compounds were determined by neutron diffraction. Structural and magnetic behaviour transitions occur as copper substitutes silicon atoms in the UCu x Si 2-x (0,28 ≤ x ≤ 0,96) solid solution. Thus, the structure of the compositions changes in the α-ThSi 2 (tetragonal) → AlB 2 (hexagonal) → Ni 2 In(hexagonal) sequence while a transition from a nonmagnetic to ferromagnetic then antiferromagnetic behaviour is observed. The magnetic properties of the different compositions are governed by a Kondo - RKKY -type interactions competition. Crystallographic disorder and magnetic frustrations are at the origin of a spin glass state between the ferro- and antiferromagnetic areas. The investigations of the GdNi 3 X 2 (X =Ga, Al, Sn) compounds revealed that their structural and magnetic properties are strongly dependent on the nature of the X element as well as the on thermal treatment. A CaCu 5 → HoNi 2,6 Ga 2,4 - type structure transition and a ferro - to antiferromagnetic behaviour evolution are favoured by the increase of the X - atom size. A commensurate modulated crystal structure (described also as a a HoNi 2,6 Ga 2,4 x a HoNi 2,6 Ga 2,4 x 2c HoNi 2,6 Ga 2,4 -type superstructure) has been observed for GdNi 3 Al 2 . Hydrogen absorption in Gd 3 Ni 6 Al 2 and GdNi 3 Al 2 weakens the strength of the magnetic interactions. (author)
METHODS FOR QUALITY ENHANCEMENT OF USER VOICE SIGNAL IN VOICE AUTHENTICATION SYSTEMS
Directory of Open Access Journals (Sweden)
O. N. Faizulaieva
2014-03-01
Full Text Available The reasonability for the usage of computer systems user voice in the authentication process is proved. The scientific task for improving the signal/noise ratio of the user voice signal in the authentication system is considered. The object of study is the process of input and output of the voice signal of authentication system user in computer systems and networks. Methods and means for input and extraction of voice signal against external interference signals are researched. Methods for quality enhancement of user voice signal in voice authentication systems are suggested. As modern computer facilities, including mobile ones, have two-channel audio card, the usage of two microphones is proposed in the voice signal input system of authentication system. Meanwhile, the task of forming a lobe of microphone array in a desired area of voice signal registration (100 Hz to 8 kHz is solved. The usage of directional properties of the proposed microphone array gives the possibility to have the influence of external interference signals two or three times less in the frequency range from 4 to 8 kHz. The possibilities for implementation of space-time processing of the recorded signals using constant and adaptive weighting factors are investigated. The simulation results of the proposed system for input and extraction of signals during digital processing of narrowband signals are presented. The proposed solutions make it possible to improve the value of the signal/noise ratio of the useful signals recorded up to 10, ..., 20 dB under the influence of external interference signals in the frequency range from 4 to 8 kHz. The results may be useful to specialists working in the field of voice recognition and speaker’s discrimination.
Chen, Peng-Fei; Sun, Wen-Yang; Ming, Fei; Huang, Ai-Jun; Wang, Dong; Ye, Liu
2018-01-01
Quantum objects are susceptible to noise from their surrounding environments, interaction with which inevitably gives rise to quantum decoherence or dissipation effects. In this work, we examine how different types of local noise under an open system affect entropic uncertainty relations for two incompatible measurements. Explicitly, we observe the dynamics of the entropic uncertainty in the presence of quantum memory under two canonical categories of noisy environments: unital (phase flip) and nonunital (amplitude damping). Our study shows that the measurement uncertainty exhibits a non-monotonic dynamical behavior—that is, the amount of the uncertainty will first inflate, and subsequently decrease, with the growth of decoherence strengths in the two channels. In contrast, the uncertainty decreases monotonically with the growth of the purity of the initial state shared in prior. In order to reduce the measurement uncertainty in noisy environments, we put forward a remarkably effective strategy to steer the magnitude of uncertainty by means of a local non-unitary operation (i.e. weak measurement) on the qubit of interest. It turns out that this non-unitary operation can greatly reduce the entropic uncertainty, upon tuning the operation strength. Our investigations might thereby offer an insight into the dynamics and steering of entropic uncertainty in open systems.
Performance evaluation of multi-channel wireless mesh networks with embedded systems.
Lam, Jun Huy; Lee, Sang-Gon; Tan, Whye Kit
2012-01-01
Many commercial wireless mesh network (WMN) products are available in the marketplace with their own proprietary standards, but interoperability among the different vendors is not possible. Open source communities have their own WMN implementation in accordance with the IEEE 802.11s draft standard, Linux open80211s project and FreeBSD WMN implementation. While some studies have focused on the test bed of WMNs based on the open80211s project, none are based on the FreeBSD. In this paper, we built an embedded system using the FreeBSD WMN implementation that utilizes two channels and evaluated its performance. This implementation allows the legacy system to connect to the WMN independent of the type of platform and distributes the load between the two non-overlapping channels. One channel is used for the backhaul connection and the other one is used to connect to the stations to wireless mesh network. By using the power efficient 802.11 technology, this device can also be used as a gateway for the wireless sensor network (WSN).
A Novel Wearable Forehead EOG Measurement System for Human Computer Interfaces.
Heo, Jeong; Yoon, Heenam; Park, Kwang Suk
2017-06-23
Amyotrophic lateral sclerosis (ALS) patients whose voluntary muscles are paralyzed commonly communicate with the outside world using eye movement. There have been many efforts to support this method of communication by tracking or detecting eye movement. An electrooculogram (EOG), an electro-physiological signal, is generated by eye movements and can be measured with electrodes placed around the eye. In this study, we proposed a new practical electrode position on the forehead to measure EOG signals, and we developed a wearable forehead EOG measurement system for use in Human Computer/Machine interfaces (HCIs/HMIs). Four electrodes, including the ground electrode, were placed on the forehead. The two channels were arranged vertically and horizontally, sharing a positive electrode. Additionally, a real-time eye movement classification algorithm was developed based on the characteristics of the forehead EOG. Three applications were employed to evaluate the proposed system: a virtual keyboard using a modified Bremen BCI speller and an automatic sequential row-column scanner, and a drivable power wheelchair. The mean typing speeds of the modified Bremen brain-computer interface (BCI) speller and automatic row-column scanner were 10.81 and 7.74 letters per minute, and the mean classification accuracies were 91.25% and 95.12%, respectively. In the power wheelchair demonstration, the user drove the wheelchair through an 8-shape course without collision with obstacles.
Development of Anodic Flux and Temperature Controlling System for Micro Direct Methanol Fuel Cell
International Nuclear Information System (INIS)
Li, M M; Liu, C; Liang, J S; Wu, C B; Xu, Z
2006-01-01
Micro Direct Methanol Fuel Cell (μDMFC) is a kind of newly developed power sources, which effective apparatus for its performance evaluation is still in urgent need at present. In this study, a testing system was established for the purpose of testing the continuous working performance such as micro flux and temperature of μDMFC. In view of the temperature controlling for micro-flux liquid fuel, a heating block with labyrinth-like single pass channel inside for heating up the methanol solution was fabricated. A semiconductorrefrigerating chip was utilized to heat and cool the liquid flow during testing procedures. On the other hand, the two channels of a high accuracy double-channel syringe pump that can suck and pump in turn so as to transport methanol solution continuously was adopted. Based on the requirements of wide-ranged temperature and micro flux controlling, the solenoid valves and the correlative component were used. A hydraulic circuit, which can circulate the fed methanol cold to hot in turn, has also been constructed to test the fatigue life of the μDMFC. The automatic control was actualized by software module written with Visual C++. Experimental results show that the system is perfect in stability and it may provide an important and advanced evaluation apparatus to satisfy the needs for real time performance testing of μDMFC
Indian Academy of Sciences (India)
Embedded system, micro-con- troller ... Embedded systems differ from general purpose computers in many ... Low cost: As embedded systems are extensively used in con- .... operating systems for the desktop computers where scheduling.
Thermal systems; Systemes thermiques
Energy Technology Data Exchange (ETDEWEB)
Lalot, S. [Valenciennes Univ. et du Hainaut Cambresis, LME, 59 (France); Lecoeuche, S. [Ecole des Mines de Douai, Dept. GIP, 59 - Douai (France)]|[Lille Univ. des Sciences et Technologies, 59 - Villeneuve d' Ascq (France); Ahmad, M.; Sallee, H.; Quenard, D. [CSTB, 38 - Saint Martin d' Heres (France); Bontemps, A. [Universite Joseph Fourier, LEGI/GRETh, 38 - Grenoble (France); Gascoin, N.; Gillard, P.; Bernard, S. [Laboratoire d' Energetique, Explosion, Structure, 18 - Bourges (France); Gascoin, N.; Toure, Y. [Laboratoire Vision et Robotique, 18 - Bourges (France); Daniau, E.; Bouchez, M. [MBDA, 18 - Bourges (France); Dobrovicescu, A.; Stanciu, D. [Bucarest Univ. Polytechnique, Faculte de Genie Mecanique (Romania); Stoian, M. [Reims Univ. Champagne Ardenne, Faculte des Sciences, UTAP/LTM, 51 (France); Bruch, A.; Fourmigue, J.F.; Colasson, S. [CEA Grenoble, Lab. Greth, 38 (France); Bontemps, A. [Universite Joseph Fourier, LEGI/GRETh, 38 - Grenoble (France); Voicu, I.; Mare, T.; Miriel, J. [Institut National des Sciences Appliquees (INSA), LGCGM, IUT, 35 - Rennes (France); Galanis, N. [Sherbrooke Univ., Genie Mecanique, QC (Canada); Nemer, M.; Clodic, D. [Ecole des Mines de Paris, Centre Energetique et Procedes, 75 (France); Lasbet, Y.; Auvity, B.; Castelain, C.; Peerhossaini, H. [Nantes Univ., Ecole Polytechnique, Lab. de Thermocinetiquede Nantes, UMR-CNRS 6607, 44 (France)
2005-07-01
This session about thermal systems gathers 26 articles dealing with: neural model of a compact heat exchanger; experimental study and numerical simulation of the thermal behaviour of test-cells with walls made of a combination of phase change materials and super-insulating materials; hydraulic and thermal modeling of a supercritical fluid with pyrolysis inside a heated channel: pre-dimensioning of an experimental study; energy analysis of the heat recovery devices of a cryogenic system; numerical simulation of the thermo-hydraulic behaviour of a supercritical CO{sub 2} flow inside a vertical tube; mixed convection inside dual-tube exchangers; development of a nodal approach with homogenization for the simulation of the brazing cycle of a heat exchanger; chaotic exchanger for the cooling of low temperature fuel cells; structural optimization of the internal fins of a cylindrical generator; a new experimental approach for the study of the local boiling inside the channels of exchangers with plates and fins; experimental study of the flow regimes of boiling hydrocarbons on a bundle of staggered tubes; energy study of heat recovery exchangers used in Claude-type refrigerating systems; general model of Carnot engine submitted to various operating constraints; the free pistons Stirling cogeneration system; natural gas supplied cogeneration system with polymer membrane fuel cell; influence of the CRN coating on the heat flux inside the tool during the wood unrolling process; transport and mixture of a passive scalar injected inside the wake of a Ahmed body; control of a laser welding-brazing process by infrared thermography; 2D self-adaptative method for contours detection: application to the images of an aniso-thermal jet; exergy and exergy-economical study of an 'Ericsson' engine-based micro-cogeneration system; simplified air-conditioning of telephone switching equipments; parametric study of the 'low-energy' individual dwelling; brief synthesis of
Data Systems vs. Information Systems
Amatayakul, Margret K.
1982-01-01
This paper examines the current status of “hospital information systems” with respect to the distinction between data systems and information systems. It is proposed that the systems currently existing are incomplete data dystems resulting in ineffective information systems.
Georgiana Marin; Mihai Catalin Andrei
2011-01-01
In recent decades IT and computer systems have evolved rapidly in economic informatics field. The goal is to create user friendly information systems that respond promptly and accurately to requests. Informatics systems evolved into decision assisted systems, and such systems are converted, based on gained experience, in expert systems for creative problem solving that an organization is facing. Expert systems are aimed at rebuilding human reasoning on the expertise obtained from experts, sto...
System on chip (SoC) microcontrollers (μC) as digitisers for ion beam analysis (IBA) instruments
Energy Technology Data Exchange (ETDEWEB)
Whitlow, Harry J., E-mail: harry.j@whitlow.se
2016-09-15
Data digitisation of the analogue signals from detectors to digital data is an essential process in ion beam analysis (IBA). The low-cost, easy availability and development environments that have a low learning threshold makes system-on-chip (SoC) microcontrollers (μC) attractive for this task. These μC combine, on one die, analogue and digital inputs and outputs with serial USB interfaces, which opens up simple implementation of tailor-made interfaces for specific IBA measurement systems. We have investigated the design and performance limitations based on development of three different digitisation interfaces for IBA. These were a two-channel nuclear instrumentation module (NIM) ADC event mode interface (EMI) for a high-resolution magnetic RBS spectrometer, a simple headless-multi-channel analyser (MCA) and a combined dual channel headless MCA and EMI. It is shown that SoC μC based interfaces for digitisation of analogue spectroscopy pulses in IBA systems can be implemented for material costs less than 100 €. The performance of the SoC devices for many IBA applications is close to what can be achieved with state-of-the-art instruments. The simple pulse spectroscopy interface circuit and software are included in the auxiliary archive.
DEFF Research Database (Denmark)
Wagner, Falko Jens
1999-01-01
Multibody Systems is one area, in which methods for solving DAEs are of special interst. This chapter is about multibody systems, why they result in DAE systems and what kind of problems that can arise when dealing with multibody systems and formulating their corresponding DAE system....
A novel FPGA-based bunch purity monitor system at the APS storage ring
International Nuclear Information System (INIS)
Norum, W.E.
2008-01-01
Bunch purity is an important source quality factor for the magnetic resonance experiments at the Advanced Photon Source. Conventional bunch-purity monitors utilizing time-to-amplitude converters are subject to dead time. We present a novel design based on a single field- programmable gate array (FPGA) that continuously processes pulses at the full speed of the detector and front-end electronics. The FPGA provides 7778 single-channel analyzers (six per rf bucket). The starting time and width of each single-channel analyzer window can be set to a resolution of 178 ps. A detector pulse arriving inside the window of a single-channel analyzer is recorded in an associated 32-bit counter. The analyzer makes no contribution to the system dead time. Two channels for each rf bucket count pulses originating from the electrons in the bucket. The other four channels on the early and late side of the bucket provide estimates of the background. A single-chip microcontroller attached to the FPGA acts as an EPICS IOC to make the information in the FPGA available to the EPICS clients.
International Nuclear Information System (INIS)
Kim, Do Hun; Mun, Tae Hun; Kim, Dong Hwan
1999-02-01
This book introduces systems thinking and conceptual tool and modeling tool of dynamics system such as tragedy of single thinking, accessible way of system dynamics, feedback structure and causal loop diagram analysis, basic of system dynamics modeling, causal loop diagram and system dynamics modeling, information delay modeling, discovery and application for policy, modeling of crisis of agricultural and stock breeding products, dynamic model and lesson in ecosystem, development and decadence of cites and innovation of education forward system thinking.
Building a new control system for the cyclotron power supplies
International Nuclear Information System (INIS)
Kormany, Z.; Lakatos, T.; Kovacs, P.; Szuecs, I.; Ander, I.
2000-01-01
Complete text of publication follows. The MGC cyclotron of the ATOMKI is a multi-particle and variable-energy machine with a rather complicated beam transport system. As a consequence, the current or voltage value of numerous power supplies should be set and adjusted by the operators during a typical run. The original control system of the cyclotron provides a traditional control desk for this purpose where the requested values can be set by using selector switches and up/down tumblers. The adjustment process with this system is completely manual and rather slow - every power supply unit gets its starting value one after the other and it typically takes 10 to 20 minutes to change the whole setting. Another disadvantage of the present system is the poor reproducibility / the analogue panel meters of the control desk cannot provide the required precision to exactly repeat a former setting. To overcome the above difficulties and speed up the adjustment process of the cyclotron and the beam transport lines, a new control system for the power supplies has been designed and is under implementation within the framework of our modernization project. Supported by the International Atomic Energy Agency, Technical Assistance Program - Project Code Number: HUN/4/013. The control of the power supplies will be changed to digital - the analogue control signals of the power stages will be produced by the D/A, the current and voltage values will be read by the A/D conversion modules of a programmable logic controller (PLC). The transition to digital control requires the development of special interface units. To separate completely the control and measuring channels from each other, they are isolated from the PLC-ground by applying opto-isolators. A two-channel (control and measurement) linear interface circuit built around the TIL 300 optical isolators has been designed, assembled and tested. It has been verified that the linearity and the precision of this circuit fulfills the
Macroscopic quantum phenomena in strongly correlated fermionic systems
International Nuclear Information System (INIS)
Rech, J.
2006-06-01
It took several years after the idea of a zero-temperature phase transition emerged to realize the impact of such a quantum critical point over a large region of the phase diagram. Observed in many experimental examples, this quantum critical regime is not yet understood in details theoretically, and one needs to develop new approaches. In the first part, we focused on the ferromagnetic quantum critical point. After constructing a controlled approach allowing us to describe the quantum critical regime, we show through the computation of the static spin susceptibility that the ferromagnetic quantum critical point is unstable, destroyed internally by an effective dynamic long-range interaction generated by the Landau damping. In the second part, we revisit the exactly screened single impurity Kondo model, using a bosonic representation of the local spin and treating it in the limit of large spin degeneracy N. We show that, in this regime, the ground-state is a non-trivial Fermi liquid, unlike what was advocated by previous similar studies. We then extend our method to encompass the physics of two coupled impurities, for which our results are qualitatively comparable to the ones obtained from various approaches carried out in the past. We also develop a Luttinger-Ward formalism, enabling us to cure some of the drawbacks of the original method used to describe the single impurity physics. Finally, we present the main ideas and the first results for an extension of the method towards the description of a Kondo lattice, relevant for the understanding of the quantum critical regime of heavy fermion materials. (authors)
International Nuclear Information System (INIS)
1988-01-01
This paper discusses progress in heavy electron research and high temperature superconductivity research. Particular topics discussed are: quadrupolar Kondo effect; coherence in the Anderson Lattice; Hall effect in heavy electron systems, suppression of supeconductivity by disorder in strongly correlated electronic materials; and charge transfer mechanisms for high temperature superconductivity
Quantum transport in strongly interacting one-dimensional nanostructures
Agundez, R.R.
2015-01-01
In this thesis we study quantum transport in several one-dimensional systems with strong electronic interactions. The first chapter contains an introduction to the concepts treated throughout this thesis, such as the Aharonov-Bohm effect, the Kondo effect, the Fano effect and quantum state transfer.
The effect of La and Y substitution on the magnetic properties of CeIn3
International Nuclear Information System (INIS)
Dijkman, W.H.; Groot, W.H. de; Boer, F.R. de; Chatel, P.F. de
1982-01-01
CeIn 3 is known to be a 'concentrated Kondo system', that is, its properties give indications of the instability of the trivalent state of cerium. To test the stability of the valence state of Ce in this compound, the authors have prepared La- and Y-substituted quasibinary compounds and performed lattice-constant, susceptibility and magnetization measurements. (Auth.)
Indian Academy of Sciences (India)
November 2010 Volume 15 Number 11. GENERAL ARTICLES. 968. Santiago Ramón y Cajal: Father of. Neurosciences. Prasanna Venkhatesh Venkataramani. 977. Counting Subspaces of a Finite Vector Space – 1. Amritanshu Prasad. 988. Quantum Transport in Mesoscopic Systems. Coulomb Blockade and Kondo Effect.
[Theory of exotic superconducting and normal states of heavy electron and high Tc materials
International Nuclear Information System (INIS)
1990-01-01
This paper discusses: quadrupole Kondo effect; heavy electron transport properties; quadrupolar fluctuation mechanism for high-T c superconductors; research accomplishments for the t--J model of high-T c superconductors; interpretation of high-T c superconductors experimental data; and dynamics of strongly correlated systems
To 'display' or not to 'display'- that is the peptide
CSIR Research Space (South Africa)
Crampton, Michael C
2008-11-01
Full Text Available eukaryotic and prokaryotic systems but has mainly focused around phages (Etz et al, 2001), yeast (Kondo and Ueda, 2004) and bacteria (Lee et al 2003). The central variable domain of the FliC protein is dispensable and can be used for the insertion and display...
Pramana – Journal of Physics | Indian Academy of Sciences
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics. E V Sampathkumaran. Articles written in Pramana – Journal of Physics. Volume 58 Issue 5-6 May-June 2002 pp 777-782 Strongly Correlated Electron Systems. Spin-glass, antiferromagnetism and Kondo behavior in Ce2Au1-CoSi3 alloys · Subham Majumdar E V ...
Energy Technology Data Exchange (ETDEWEB)
Rech, J
2006-06-15
It took several years after the idea of a zero-temperature phase transition emerged to realize the impact of such a quantum critical point over a large region of the phase diagram. Observed in many experimental examples, this quantum critical regime is not yet understood in details theoretically, and one needs to develop new approaches. In the first part, we focused on the ferromagnetic quantum critical point. After constructing a controlled approach allowing us to describe the quantum critical regime, we show through the computation of the static spin susceptibility that the ferromagnetic quantum critical point is unstable, destroyed internally by an effective dynamic long-range interaction generated by the Landau damping. In the second part, we revisit the exactly screened single impurity Kondo model, using a bosonic representation of the local spin and treating it in the limit of large spin degeneracy N. We show that, in this regime, the ground-state is a non-trivial Fermi liquid, unlike what was advocated by previous similar studies. We then extend our method to encompass the physics of two coupled impurities, for which our results are qualitatively comparable to the ones obtained from various approaches carried out in the past. We also develop a Luttinger-Ward formalism, enabling us to cure some of the drawbacks of the original method used to describe the single impurity physics. Finally, we present the main ideas and the first results for an extension of the method towards the description of a Kondo lattice, relevant for the understanding of the quantum critical regime of heavy fermion materials. (authors)
Coupling component systems towards systems of systems
Autran , Frédéric; Auzelle , Jean-Philippe; Cattan , Denise; Garnier , Jean-Luc; Luzeaux , Dominique; Mayer , Frédérique; Peyrichon , Marc; Ruault , Jean-René
2008-01-01
International audience; Systems of systems (SoS) are a hot topic in our "fully connected global world". Our aim is not to provide another definition of what SoS are, but rather to focus on the adequacy of reusing standard system architecting techniques within this approach in order to improve performance, fault detection and safety issues in large-scale coupled systems that definitely qualify as SoS, whatever the definition is. A key issue will be to secure the availability of the services pr...
Habayeb, A R
1987-01-01
Highlights three principal applications of system effectiveness: hardware system evaluation, organizational development and evaluation, and conflict analysis. The text emphasizes the commonality of the system effectiveness discipline. The first part of the work presents a framework for system effectiveness, partitioning and hierarchy of hardware systems. The second part covers the structure, hierarchy, states, functions and activities of organizations. Contains an extended Appendix on mathematical concepts and also several project suggestions.
International Nuclear Information System (INIS)
Meyer, P.J.
1981-01-01
Systems included under the heading ''Reactor Auxillary Systems'' are those immediately involved with the reactor operation. These include the systems for dosing and letdown of reactor coolant, as well as for the chemical dosing, purification and treatment of the reactor coolant and the cooling system in the controlled area. The ancillary systems are mainly responsible for liquid and gaseous treatment and the waste treatment for final storage. (orig.)
PREFACE: Dynamics of low-dimensional systems Dynamics of low-dimensional systems
Bernasconi, M.; Miret-Artés, S.; Toennies, J. P.
2012-03-01
Chulkov Surface phonons on Pb(111) I Yu Sklyadneva, R Heid, K-P Bohnen, P M Echenique and E V Chulkov Using evidence from nanocavities to assess the vibrational properties of external surfaces G F Cerofolini, F Corni, S Frabboni, G Ottaviani, E Romano, R Tonini and D Narducci Magnetic properties and relaxation dynamics of a frustrated Ni7 molecular nanomagnet E Garlatti, S Carretta, M Affronte, E C Sañudo, G Amoretti and P Santini A theoretical study of rotational and translational diffusion dynamics of molecules with a six-fold point symmetry adsorbed on a hexagonal lattice by neutron scattering I Calvo-Almazán, S Miret-Artés and P Fouquet Vibrational dynamics and surface structure of Bi(111) from helium atom scattering measurements M Mayrhofer-Reinhartshuber, A Tamtögl, P Kraus, K H Rieder and W E Ernst Double and triple ionization of silver clusters by electron impactAvik Halder, Anthony Liang, Chunrong Yin and Vitaly V Kresin Scattering of O2 from a graphite surface W W Hayes, Junepyo Oh, Takahiro Kondo, Keitaro Arakawa, Yoshihiko Saito, Junji Nakamura and J R Manson Zero-phonon lines of systems with different dimensions and unconventional vibronic interactions V Hizhnyakov A kinetic Monte Carlo approach to investigate antibiotic translocation through bacterial porins Matteo Ceccarelli, Attilio V Vargiu and Paolo Ruggerone Quantum Zeno and anti-Zeno effects in surface diffusion of interacting adsorbates H C Peñate-Rodrìguez, R Martìnez-Casado, G Rojas-Lorenzo, A S Sanz and S Miret-Artés Weakly bound finite systems: (4He)N-Rb2(3Σu), clustering structures from a quantum Monte Carlo approach D López-Durán, R Rodrìguez-Cantano, T González-Lezana, G Delgado-Barrio, P Villarreal, E Yurtsever and F A Gianturco Multiphonon atom-surface scattering from corrugated surfaces: derivation of the inelastic scattering spectrum for diffraction statesBranko Gumhalter Probing the non-pairwise interactions between CO molecules moving on a Cu(111) surfacePepijn R Kole, Holly
Anisotropic magnetic phase diagram of Kondo-Lattice compound Ce3Pd20Ge6 with quadrupolar ordering
International Nuclear Information System (INIS)
Kitagawa, Jiro; Takeda, Naoya; Ishikawa, Masayasu; Yoshida, Toshiya; Ishiguro, Akiko; Kimura, Noriaki; Komatsubara, Takemi
1999-01-01
We have measured the specific heat and the electrical resistivity of Ce 3 Pd 20 Ge 6 in magnetic fields up to 4T applied along three principal directions. The compound shows the large negative magnetoresistance in the quadrupolar phase. The coefficient of the electronic specific heat and T 2 -coefficient of the electrical resistivity are considerably reduced at 4T. The magnetic phase diagram constructed from these measurements suggests the existence of a highly anisotropic interaction between the electric quadrupolar moments and the magnetic dipolar moments. (author)
Directory of Open Access Journals (Sweden)
Takumasa Kondo Kondo
2014-01-01
Full Text Available The fluted scale Crypticerya multicicatrices (Hemiptera: Monophlebidae is an invasive insect that became a major pest on the island of San Andrés. To generate control strategies for this insect, its distribution and infestation levels on palm species, fruit trees, leguminous trees and other plant species were determined during January 14–18, 2013. A total of 96 points were sampled in order to determine the distribution of the insect on the island. During the study, the fluted scale was found distributed throughout the island of San Andrés, including Haynes Cay and Johnny Cay. The palms were the plants with the highest levels of infestation, 70.8% had some degree of infestation (37.5% high infestation levels; followed by fruit trees which had 65.6% with some degree of infestation (30.2% high infestation levels; followed by leguminous trees which had 59.6% with some degree of infestation (13.5% high infestation levels and finally “other hosts” which had 51.1% with some level of infestation (11.5% high infestation levels. This study is the first detailed mapping of C. multicicatrices on the island of San Andrés which will become the basis for future work on the population dynamics of the fluted scale and its distribution on the island.
International Nuclear Information System (INIS)
Malik, S.K.; Menon, L.; Pecharsky, V.K.; Gschneidner, K.A. Jr.
1997-01-01
The compound CeRhSb is a mixed valent Ce-based compound which shows a gap in the electronic density of states at low temperatures. The gap manifests by a rise in electrical resistivity below about 8 K from which the gap energy is estimated to be about 4 K. We have carried out heat capacity measurements on this compound in various applied fields up to 9.85 T. The magnetic contribution to the heat capacity, ΔC, is found to have a maximum in ΔC/T vs T at 10 K, below which ΔC/T is linear with T. This is attributed to the fact that below this temperature, in the gapped state, the electronic density of states decreases linearly with decreasing temperature. On application of a magnetic field, the electronic specific heat coefficient γ in the gapped state increases by ∼4mJ/molK 2 . The maximum in ΔC/T vs T is observed in all fields, which shifts to lower temperatures ∼1K at 5.32 T and raises again at 9.85 T to about the same values as at H=0T. This suggests that the gap exists for all fields up to 9.85 T. Above 10 K, in the mixed-valent state, ΔC/T vs T decreases with increasing temperature in zero field. There is hardly any effect of application of field in the mixed-valent state. We have also carried out magnetoresistance measurements on CeRhSb up to fields of 5.5 T at 2, 4.5, 10, 20, and 30 K. The magnetoresistance in CeRhSb is positive at temperatures of 4.5 K and above, in applied fields up to 5.5 T. At 5.5 T, the magnetoresistance is maximum at 4.5 K (6%) and decreases with increasing temperature. The observation of the maximum is consistent with the observation of a maximum in ΔC/T vs T and is due to a change in the density of states. At a temperature of 2 K, a negative magnetoresistance is observed for magnetic fields greater than ∼3.5T which suggests reduction in the gap. copyright 1997 The American Physical Society
Directory of Open Access Journals (Sweden)
Jan Lánský
2017-06-01
Full Text Available Cryptocurrency systems are purely digital and decentralized systems that use cryptographic principles to confirm transactions. Bitcoin is the first and also the most widespread cryptocurrency. The aim of this article is to introduce Bitcoin system using a language understandable also to readers without computer science education. This article captures the Bitcoin system from three perspectives: internal structure, network and users. Emphasis is placed on brief and clear definitions (system components and their mutual relationships. A new system view of the stated terms constitutes author’s own contribution.
The functional renormalization group for interacting quantum systems with spin-orbit interaction
International Nuclear Information System (INIS)
Grap, Stephan Michael
2013-01-01
We studied the influence of spin-orbit interaction (SOI) in interacting low dimensional quantum systems at zero temperature within the framework of the functional renormalization group (fRG). Among the several types of spin-orbit interaction the so-called Rashba spin-orbit interaction is especially intriguing for future spintronic applications as it may be tuned via external electric fields. We investigated its effect on the low energy physics of an interacting quantum wire in an applied Zeeman field which is modeled as a generalization of the extended Hubbard model. To this end we performed a renormalization group study of the two particle interaction, including the SOI and the Zeeman field exactly on the single particle level. Considering the resulting two band model, we formulated the RG equations for the two particle vertex keeping the full band structure as well as the non trivial momentum dependence of the low energy two particle scattering processes. In order to solve these equations numerically we defined criteria that allowed us to classify whether a given set of initial conditions flows towards the strongly coupled regime. We found regions in the models parameter space where a weak coupling method as the fRG is applicable and it is possible to calculate additional quantities of interest. Furthermore we analyzed the effect of the Rashba SOI on the properties of an interacting multi level quantum dot coupled to two semi in nite leads. Of special interest was the interplay with a Zeeman field and its orientation with respect to the SOI term. We found a renormalization of the spin-orbit energy which is an experimental quantity used to asses SOI effects in transport measurements, as well as renormalized effective g factors used to describe the Zeeman field dependence. In particular in asymmetrically coupled systems the large parameter space allows for rich physics which we studied by means of the linear conductance obtained via the generalized Landauer
"Calibration" system for spectral measurements and its experimental results
Bruchkouskaya, Sviatlana I.; Katkovsky, Leonid V.; Belyaev, Boris I.; Malyshev, Vladislav B.
2017-04-01
"Calibration" system has been developed at A. N. Sevchenko Research Institute of Applied Physical Problems of the Belarusian State University. It was designed for measuring the characteristics of spectral reflectance of all types of natural surfaces (test sites) in ground conditions or on board of aircraft carriers and has the following components: - Photospectroradiometr (PhSR) of high resolution with a range of 400-900 nm, equipped with a digital time-lapse video system; - Two-channel modular spectroradiometer (TMS) with a range of 400-900 nm, designed for simultaneous measurements of reflected light brightness of the underlying surface and the incident radiation from the upper hemisphere; - Two portable spectroradiometers (PSR-700 and PSR-1300) with a spectral range 800-1500 nm; 1200-2500 nm; - Scanning solar spectropolarimeter (SSP-600) with a range of 350-950 nm for measurements of direct sunlight and scattered by the atmosphere at different angles; "Calibration" system provides spectral resolution of 5.2 nm in a range of 400-900 nm, 10 nm in a range of 800-1500 nm and 15 nm in a range of 1200-2500 nm. Measurements of the optical characteristics of solar radiation (for determining parameters of the atmosphere) and that of underlying surface are synchronous. There is also a set of special nozzles for measurements of spectral brightness coefficients, polarization characteristics and spectral albedo. Spectra and images are geotagged to the navigation data (time, GPS). For the measurements of spectral reflection dependencies within "Monitoring-SG" framework expeditions to the Kuril Islands, Kursk aerospace test site and Kamchatka Peninsula were conducted in 2015 and 2016. The spectra of different underlying surfaces have been obtained: soils, plants and water objects, sedimentary and volcanic rocks. These surveys are a valuable material for further researches and selection of test facilities for flight calibration of space imaging systems. Information obtained
International Nuclear Information System (INIS)
Honeck, H.C.
1975-04-01
A major computational system called JOSHUA has been under development at the Savannah River Laboratory since 1968. The JOSHUA System has two major parts: the Operating System and the Application System. The Operating System has been in production use since 1970 and provides data management, terminal, and job execution facilities. The Application System uses these facilities in solving problems in reactor physics and engineering. Features of the Application System are the two-dimensional lattice physics and three-dimensional transient reactor physics capabilities, which have been in use since 1971 and 1974, respectively. The capabilities of the JOSHUA System are summarized, and statistics on size, use, and development effort are provided. (U.S.)
Cabrera, Derek; Colosi, Laura; Lobdell, Claire
2008-08-01
Evaluation is one of many fields where "systems thinking" is popular and is said to hold great promise. However, there is disagreement about what constitutes systems thinking. Its meaning is ambiguous, and systems scholars have made diverse and divergent attempts to describe it. Alternative origins include: von Bertalanffy, Aristotle, Lao Tsu or multiple aperiodic "waves." Some scholars describe it as synonymous with systems sciences (i.e., nonlinear dynamics, complexity, chaos). Others view it as taxonomy-a laundry list of systems approaches. Within so much noise, it is often difficult for evaluators to find the systems thinking signal. Recent work in systems thinking describes it as an emergent property of four simple conceptual patterns (rules). For an evaluator to become a "systems thinker", he or she need not spend years learning many methods or nonlinear sciences. Instead, with some practice, one can learn to apply these four simple rules to existing evaluation knowledge with transformative results.
DEFF Research Database (Denmark)
The tutorial will discuss the definition of cognitive systems as the possibilities to extend the current systems engineering paradigm in order to perceive, learn, reason and interact robustly in open-ended changing environments. I will also address cognitive systems in a historical perspective...... to be modeled within a limited set of predefined specifications. There will inevitably be a need for robust decisions and behaviors in novel situations that include handling of conflicts and ambiguities based on the capability and knowledge of the artificial cognitive system. Further, there is a need...... in cognitive systems include e.g. personalized information systems, sensor network systems, social dynamics system and Web2.0, and cognitive components analysis. I will use example from our own research and link to other research activities....
Schomaker, Verner; Lingafelter, E. C.
1985-01-01
Discusses characteristics of crystal systems, comparing (in table format) crystal systems with lattice types, number of restrictions, nature of the restrictions, and other lattices that can accidently show the same metrical symmetry. (JN)
International Nuclear Information System (INIS)
Vanin, V.R.
1990-01-01
The multidetector systems for high resolution gamma spectroscopy are presented. The observable parameters for identifying nuclides produced simultaneously in the reaction are analysed discussing the efficiency of filter systems. (M.C.K.)
International Nuclear Information System (INIS)
Haldy, P.A.
1988-01-01
The definitions of the terms 'artificial intelligence' and 'expert systems', the methodology, areas of employment and limits of expert systems are discussed. The operation of an expert system is described, especially the presentation and organization of knowledge as well as interference and control. Methods and tools for expert system development are presented and their application in nuclear energy are briefly addressed. 7 figs., 2 tabs., 6 refs
DEFF Research Database (Denmark)
Hildebrandt, Thomas Troels; Cattani, Gian Luca
2016-01-01
An expert system is a computer system for inferring knowledge from a knowledge base, typically by using a set of inference rules. When the concept of expert systems was introduced at Stanford University in the early 1970s, the knowledge base was an unstructured set of facts. Today the knowledge b...... for the application of expert systems, but also raises issues regarding privacy and legal liability....
DEFF Research Database (Denmark)
Rose, Jørgen
1997-01-01
This report gives an overview of the different retrofitting possibilities that are available today. The report looks at both external and internal systems for external wall constructions, roof constructions, floor constructions and foundations. All systems are described in detail in respect to use...... and methods, and the efficiency of the different systems are discussed....
Non-linear quantum critical dynamics and fluctuation-dissipation ratios far from equilibrium
Energy Technology Data Exchange (ETDEWEB)
Zamani, Farzaneh [Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Str. 38, 01187 Dresden (Germany); Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden (Germany); Ribeiro, Pedro [CeFEMA, Instituto Superior Tcnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Russian Quantum Center, Novaya Street 100 A, Skolkovo, Moscow Area, 143025 (Russian Federation); Kirchner, Stefan, E-mail: stefan.kirchner@correlated-matter.com [Center for Correlated Matter, Zhejiang University, Hangzhou, Zhejiang 310058 (China)
2016-02-15
Non-thermal correlations of strongly correlated electron systems and the far-from-equilibrium properties of phases of condensed matter have become a topical research area. Here, an overview of the non-linear dynamics found near continuous zero-temperature phase transitions within the context of effective temperatures is presented. In particular, we focus on models of critical Kondo destruction. Such a quantum critical state, where Kondo screening is destroyed in a critical fashion, is realized in a number of rare earth intermetallics. This raises the possibility of experimentally testing for the existence of fluctuation-dissipation relations far from equilibrium in terms of effective temperatures. Finally, we present an analysis of a non-interacting, critical reference system, the pseudogap resonant level model, in terms of effective temperatures and contrast these results with those obtained near interacting quantum critical points. - Highlights: • Critical Kondo destruction explains the unusual properties of quantum critical heavy fermion compounds. • We review the concept of effective temperatures in models of critical Kondo destruction. • We compare effective temperatures found near non-interacting and fully interacting fixed points. • A comparison with non-interacting quantum impurity models is presented.
International Nuclear Information System (INIS)
Wauthier, J.; Fiori, R.
1990-01-01
The development, the characteristics and the applications of a multifunction system are presented. The system is used on the RBES laboratory pipes, at Marcoule. The system was developed in order to allow, without time loss, the modification of the circuit function by replacing only one component. The following elements form the multifunction system: a fixed base, which is part of the tube, a removable piece, which is inserted into the base, a cover plate and its locking system. The material, chosen among commercial trade marks, required small modifications in order to be used in the circuit [fr
Tsichritzis, Dionysios C; Rheinboldt, Werner
1974-01-01
Operating Systems deals with the fundamental concepts and principles that govern the behavior of operating systems. Many issues regarding the structure of operating systems, including the problems of managing processes, processors, and memory, are examined. Various aspects of operating systems are also discussed, from input-output and files to security, protection, reliability, design methods, performance evaluation, and implementation methods.Comprised of 10 chapters, this volume begins with an overview of what constitutes an operating system, followed by a discussion on the definition and pr
Radiation control monitoring system on the High Temperature Engineering Test Reactor
International Nuclear Information System (INIS)
Minowa, Y.; Nakazawa, T.; Sato, K.; Kikuchi, H.; Nomura, T.
1999-01-01
Radiation control monitoring system of the HTTR is divided into three subsystems; exhaust monitoring equipment, room air monitoring equipment, dose equivalent rate monitoring equipment. The exhaust monitoring equipment consists of exhaust gas monitors, exhaust dust monitors, and a tritium and carbon sampling device at normal operation of the reactor. Accident gas monitors are also provided for the emergency. The tritium and carbon sampling device uses cupper oxide as a oxidizer, and ethanol amine as a sampling materials which collects continuously tritium and carbon in dust during about one month and is measured by a liquid scintillation counter. The accident gas monitors consist of two channels, for a low and a high range. The high range-gas monitor consists of two ionization chambers: one encloses argon gas and the other encloses xenon gas. Average energy of various gamma-rays, hence, accident exposure dose of the public can be estimated with the comparison of the sensitivity of two kinds of ionization chambers. The dose equivalent rate monitoring equipment consists of silicon semiconductor detectors for gamma-ray, a ionization chamber for gamma-ray, a BF 3 counter for neutron, and accident area monitors which are located in the reactor container. The message of 'check dose !' or 'temporary evacuation !' can be send to the workers in the reactor with a light and a sound. A computer system collects the radiation monitoring data every 10 sec cycle and accumulates them in a server computer. The leakage and the dispersion of helium gas must be taken into account on the radiation control monitoring system of the HTTR. (Suetake, M.)
Siemieniuch, C E; Sinclair, M A
2006-01-01
The paper presents a view of systems integration, from an ergonomics/human factors perspective, emphasising the process of systems integration as is carried out by humans. The first section discusses some of the fundamental issues in systems integration, such as the significance of systems boundaries, systems lifecycle and systems entropy, issues arising from complexity, the implications of systems immortality, and so on. The next section outlines various generic processes for executing systems integration, to act as guides for practitioners. These address both the design of the system to be integrated and the preparation of the wider system in which the integration will occur. Then the next section outlines some of the human-specific issues that would need to be addressed in such processes; for example, indeterminacy and incompleteness, the prediction of human reliability, workload issues, extended situation awareness, and knowledge lifecycle management. For all of these, suggestions and further readings are proposed. Finally, the conclusions section reiterates in condensed form the major issues arising from the above.
International Nuclear Information System (INIS)
Kagan, D.N.; Hubberstey, P.; Barker, M.G.
1985-01-01
The paper reviews the experimental and theoretical studies carried out on multicomponent alkali metal systems. Solid-liquid phase equilibria studies are mainly concerned with the systems Na-K-Rb and Na-K-Cs, and data on the liquidus temperatures in these systems are presented. The thermodynamic properties of the ternary Na-K-Cs eutectic system have been determined experimentally, and the enthalpy, heat capacity and excess functions of the alloy are given. An analysis of calculational methods used in determining thermodynamic functions of ternary liquid metals systems is described. Finally, data are tabulated for the density, compressibility, saturated vapour pressure, viscosity and thermal conductivity of the ternary Na-K-Cs eutectic system. (UK)
Kembellec, Gérald; Saleh, Imad
2014-01-01
Acclaimed by various content platforms (books, music, movies) and auction sites online, recommendation systems are key elements of digital strategies. If development was originally intended for the performance of information systems, the issues are now massively moved on logical optimization of the customer relationship, with the main objective to maximize potential sales. On the transdisciplinary approach, engines and recommender systems brings together contributions linking information science and communications, marketing, sociology, mathematics and computing. It deals with the understan
DEFF Research Database (Denmark)
Jensen, Mads Brath; Mortensen, Henrik Rubæk; Mullins, Michael
2009-01-01
This paper describes and reflects upon the results of an investigative project which explores the setting up of a material system - a parametric and generative assembly consisting of and taking into consideration material properties, manufacturing constraints and geometric behavior. The project...... approaches the subject through the construction of a logic-driven system aiming to explore the possibilities of a material system that fulfills spatial, structural and performative requirements concurrently and how these are negotiated in situations where they might be conflicting....
Vaughan, William W.
2016-01-01
The term “systems engineering” when entered into the Google search page, produces a significant number of results, evidence that systems engineering is recognized as being important for the success of essentially all products. Since most readers of this item will be rather well versed in documents concerning systems engineering, I have elected to share some of the points made on this subject in a document developed by the European Cooperation for Space Standardization (ECSS), a component of t...
Coherence and spin effects in quantum dots
International Nuclear Information System (INIS)
Katsumoto, S
2007-01-01
This review focuses on experiments on coherent transport through quantum dot systems. The most important quantity obtained in coherent transport is the phase shift through the dots, which gives complementary information to the scattering amplitude (i.e. the conductance). However, two-terminal devices have a particular difficulty, called 'phase rigidity', in obtaining the phase shift. There are two representative ways to avoid this problem: one is to adopt a multi-terminal configuration and another is to use resonance in the interferometer. This review mainly reviews the latter approaches. Such resonance in the whole interferometer often joins with local resonance inside the interferometer and appears as the Fano effect, which is a powerful tool for investigating the phase shift problem with the aid of theories. In addition to such resonances of single-electron states, electron spin causes a kind of many-body resonance, that is, the Kondo effect. Combination of these resonances is the Fano-Kondo effect. Experiments on the Fano-Kondo effect, which unveil the nature of the Kondo resonance, are also reviewed. (topical review)
Federal Laboratory Consortium — The Energetic Systems Division provides full-spectrum energetic engineering services (project management, design, analysis, production support, in-service support,...
Irwin, J David
2011-01-01
Technology has now progressed to the point that intelligent systems are replacing humans in the decision making processes as well as aiding in the solution of very complex problems. In many cases intelligent systems are already outperforming human activities. Artificial neural networks are not only capable of learning how to classify patterns, such images or sequence of events, but they can also effectively model complex nonlinear systems. Their ability to classify sequences of events is probably more popular in industrial applications where there is an inherent need to model nonlinear system
Winther, Rasmus Grønfeldt
2008-08-19
Darwin's 19th century evolutionary theory of descent with modification through natural selection opened up a multidimensional and integrative conceptual space for biology. We explore three dimensions of this space: explanatory pattern, levels of selection, and degree of difference among units of the same type. Each dimension is defined by a respective pair of poles: law and narrative explanation, organismic and hierarchical selection, and variational and essentialist thinking. As a consequence of conceptual debates in the 20th century biological sciences, the poles of each pair came to be seen as mutually exclusive opposites. A significant amount of 21st century research focuses on systems (e.g., genomic, cellular, organismic, and ecological/global). Systemic Darwinism is emerging in this context. It follows a "compositional paradigm" according to which complex systems and their hierarchical networks of parts are the focus of biological investigation. Through the investigation of systems, Systemic Darwinism promises to reintegrate each dimension of Darwin's original logical space. Moreover, this ideally and potentially unified theory of biological ontology coordinates and integrates a plurality of mathematical biological theories (e.g., self-organization/structure, cladistics/history, and evolutionary genetics/function). Integrative Systemic Darwinism requires communal articulation from a plurality of perspectives. Although it is more general than these, it draws on previous advances in Systems Theory, Systems Biology, and Hierarchy Theory. Systemic Darwinism would greatly further bioengineering research and would provide a significantly deeper and more critical understanding of biological reality.
Hoff, Karla
2016-01-01
In standard economics, individuals are rational actors and economic forces undermine institutions that impose large inefficiencies. The persistence of the caste system is evidence of the need for psychologically more realistic models of decision-making in economics. The caste system divides South Asian society into hereditary groups whose lowest ranks are represented as innately polluted. ...
Lu L.; Medo M.; Yeung C.H.; Zhang Y.-C.; Zhang Z.-K.; Zhou T.
2012-01-01
The ongoing rapid expansion of the Internet greatly increases the necessity of effective recommender systems for filtering the abundant information. Extensive research for recommender systems is conducted by a broad range of communities including social and computer scientists, physicists, and interdisciplinary researchers. Despite substantial theoretical and practical achievements, unification and comparison of different approaches are lacking, which impedes further advances. In this article...
International Nuclear Information System (INIS)
Ohyama, Takuya; Saegusa, Hiromitsu
2009-03-01
As a part of the research and development regarding characterisation of deep geological environment, the GEOMASS (GEOLOGICAL MODELLING ANALYSIS AND SIMULATION SOFTWARE) system has been developed by the Japan Atomic Energy Agency in order to carry out geological and hydrogeological modelling and groundwater flow simulation and so on. The GEOMASS system integrates a commercial geological interpretation system (EarthVision), which is used for geological modelling and visualisation, with a proprietary code for groundwater flow (FracAffinity). This integrated system allows users to make rapid improvement of models as data increases. Also, it is possible to perform more realistic groundwater flow simulation due to the capability of modelling the rock mass as a continuum with discrete hydro-structural features in the rock mass. This paper consists of 'Overview of GEOMASS system', FracAffinity Theoretical Background' and 'FracAffinity User Guide' and is edited as a GEOMASS system manual. 'Overview of GEOMASS system' describes the outline of this system. 'FracAffinity Theoretical Background' describes the information of technical background of FracAffinity software. FracAffinity User Guide' describes the structure of the FracAffinity input files, the usage of FracAffinity Interface and flow-solver. Updating of the FracAffinity has been continued as needed and FracAffinity version3.3 is the latest version at present (July 2008). (author)
Systems integration (automation system). System integration (automation system)
Energy Technology Data Exchange (ETDEWEB)
Fujii, K; Komori, T; Fukuma, Y; Oikawa, M [Nippon Steal Corp., Tokyo (Japan)
1991-09-26
This paper introduces business activities on an automation systems integration (SI) started by a company in July,1988, and describes the SI concepts. The business activities include, with the CIM (unified production carried out on computers) and AMENITY (living environment) as the mainstays, a single responsibility construction ranging from consultation on structuring optimal systems for processing and assembling industries and intelligent buildings to system design, installation and after-sales services. With an SI standing on users {prime} position taken most importantly, the business starts from a planning and consultation under close coordination. On the conceptual basis of structuring optimal systems using the ompany {prime}s affluent know-hows and tools and adapting and applying with multi-vendors, open networks, centralized and distributed systems, the business is promoted with the accumulated technologies capable of realizing artificial intelligence and neural networks in its background, and supported with highly valuable business results in the past. 10 figs., 1 tab.
DEFF Research Database (Denmark)
Manelius, Anne-Mette; Beim, Anne
2007-01-01
Opsamling af diskussioner på konferencen og udstillingen Creative Systems i september/oktober 2007. Konferencen og Udstillingen Creative Systems sætter fokus på systemer som en positiv drivkraft i den kreative skabelsesproces. CINARK inviterede fire internationale kapaciteter, som indenfor hver...... deres felt har beskæftiget sig med udviklingen af systemer. Kieran Timberlake, markant amerikansk tegnestue; Mark West, Professor på University of Manitoba, Canada, og pioner indenfor anvendelse af tekstilforskalling til betonstøbninger; Matilda McQuaid, Arkitekturhistoriker og kurator på udstillingen...... om Extreme Textiles på amerikanske Cooper Hewit Design Museum, samt Professor Ludger Hovestadt, ved ETH, Zürich der fokuserer på udvikling og anvendelse af logaritmiske systemtilgange. Udstillingen diskuterede ud fra deres meget forskellige arbejder, det kreative potentiale i anvendelsen af systemer...
DEFF Research Database (Denmark)
Aceto, Luca; Ingolfsdottir, Anna; Larsen, Kim Guldstrand
A reactive system comprises networks of computing components, achieving their goals through interaction among themselves and their environment. Thus even relatively small systems may exhibit unexpectedly complex behaviours. As moreover reactive systems are often used in safety critical systems......, the need for mathematically based formal methodology is increasingly important. There are many books that look at particular methodologies for such systems. This book offers a more balanced introduction for graduate students and describes the various approaches, their strengths and weaknesses, and when...... they are best used. Milner's CCS and its operational semantics are introduced, together with the notions of behavioural equivalences based on bisimulation techniques and with recursive extensions of Hennessy-Milner logic. In the second part of the book, the presented theories are extended to take timing issues...
Energy Technology Data Exchange (ETDEWEB)
Hong, Sung Soo; Ryoo, Won; Chung, Gui Yung [Hong-Ik University, Seoul (Korea, Republic of); Chun, Myung-Suk [Korea Institute of Science and Technology (KIST), Seoul (Korea, Republic of)
2014-02-15
In the spiral wound module of the pressure-retarded osmosis (PRO) system for the salinity gradient power generation, effects of the inlet pressure differences between feed-channel and draw-channel were studied. Fluxes of water and solute through membrane and power were estimated. The water flux through membrane decreased along the x-direction and increased along the y-direction with the increase of inlet pressure differences between two channels. On the other hand, the solute flux through membrane showed the opposite trend. The concentration of flow in the feed-channel increased a lot along the y-direction and that in the draw-channel decreased along the x-direction. In our system, for the inlet pressure differences of 1-11 atm, the flow rate in the feed-channel decreased about 8-13% and that in the draw-channel increased by the same amount. The power density increased and then decreased with the increasing inlet pressure difference.
International Nuclear Information System (INIS)
Hong, Sung Soo; Ryoo, Won; Chung, Gui Yung; Chun, Myung-Suk
2014-01-01
In the spiral wound module of the pressure-retarded osmosis (PRO) system for the salinity gradient power generation, effects of the inlet pressure differences between feed-channel and draw-channel were studied. Fluxes of water and solute through membrane and power were estimated. The water flux through membrane decreased along the x-direction and increased along the y-direction with the increase of inlet pressure differences between two channels. On the other hand, the solute flux through membrane showed the opposite trend. The concentration of flow in the feed-channel increased a lot along the y-direction and that in the draw-channel decreased along the x-direction. In our system, for the inlet pressure differences of 1-11 atm, the flow rate in the feed-channel decreased about 8-13% and that in the draw-channel increased by the same amount. The power density increased and then decreased with the increasing inlet pressure difference
Directory of Open Access Journals (Sweden)
M S Islam
2010-03-01
Full Text Available Cross-phase modulation (XPM changes the state-of-polarization (SOP of the channels through nonlinear polarization rotation and induces nonlinear time dependent phase shift for polarization components that leads to amplitude modulation of the propagating waves in a wavelength division multiplexing (WDM system. Due to the presence of birefringence, the angle between the SOP changes randomly and as a result polarization mode dispersion (PMD causes XPM modulation amplitude fluctuation random in the perturbed channel. In this paper we analytically determine the probability density function of the random angle between the SOP of pump and probe, and evaluate the impact of polarization mode dispersion on XPM in terms of bit error rate, channel spacing etc for a two channel intensity modulation-direct detection WDM system at 10 Gb/s. It is found that the XPM induced crosstalk is polarization independent for channel spacing greater than 3 nm or PMD coefficient larger than 2 ps/√km. We also investigate the dependence of SOP variance on PMD coefficient and channel spacing.
Upgraded RECOVER system - CASDAC system
International Nuclear Information System (INIS)
Yamamoto, Yoichi; Koyama, Kinji
1992-03-01
The CASDAC (Containment And Surveillance Data Authenticated Communication) system has been developed by JAERI for nuclear safeguards and physical protection of nuclear material. This system was designed and constructed as an upgraded RECOVER system, design concept of which was based on the original RECOVER system and also the TRANSEAVER system. Both of them were developed several years ago as a remote monitoring system for continual verification of security and safeguards status of nuclear material. The system consists of two subsystems, one of them is a Grand Command Center (GCC) subsystem and the other is a facility subsystem. Communication between the two subsystems is controlled through the international telephone line network. Therefore all communication data are encrypted to prevent access by an unauthorized person who may intend to make a falsification, or tapping. The facility subsystem has an appropriate measure that ensure data security and reliable operation under unattended mode of operator. The software of this system is designed so as to be easily used in other different types of computers. This report describes the outline of the CASDAC system and the results of its performance test. This work has been carried out in the framework of Japan Support Programme for Agency Safeguards (JASPAS) as a project, JA-1. (author)
Charge Aspects of Composite Pair Superconductivity
Flint, Rebecca
2014-03-01
Conventional Cooper pairs form from well-defined electronic quasiparticles, making the internal structure of the pair irrelevant. However, in the 115 family of superconductors, the heavy electrons are forming as they pair and the internal pair structure becomes as important as the pairing mechanism. Conventional spin fluctuation mediated pairing cannot capture the direct transition from incoherent local moments to heavy fermion superconductivity, but the formation of composite pairs favored by the two channel Kondo effect can. These composite pairs are local d-wave pairs formed by two conduction electrons in orthogonal Kondo channels screening the same local moment. Composite pairing shares the same symmetries as magnetically mediated pairing, however, only composite pairing necessarily involves a redistribution of charge within the unit cell originating from the internal pair structure, both as a monopole (valence change) and a quadrupole effect. This redistribution will onset sharply at the superconducting transition temperature. A smoking gun test for composite pairing is therefore a sharp signature at Tc - for example, a cusp in the Mossbauer isomer shift in NpPd5Al2 or in the NQR shift in (Ce,Pu)CoIn5.
DEFF Research Database (Denmark)
Madsen, Tanja Kidholm Osmann; Bahnsen, Chris Holmberg; Jensen, Morten Bornø
This deliverable is part of WP4. Overall WP4 is motivated by the need for automatic systems that can ease the task of annotating massive amounts of traffic data. Concretely this deliverable is related to WP4.2 - the watchdog system. The idea with the watchdog is to develop a system that can remov...... huge chunks of video data where no events/interactions of interest are occurring and hence let a user focus on manually annotation of only the interesting stuff....
Sternberg, Shlomo
2010-01-01
Celebrated mathematician Shlomo Sternberg, a pioneer in the field of dynamical systems, created this modern one-semester introduction to the subject for his classes at Harvard University. Its wide-ranging treatment covers one-dimensional dynamics, differential equations, random walks, iterated function systems, symbolic dynamics, and Markov chains. Supplementary materials offer a variety of online components, including PowerPoint lecture slides for professors and MATLAB exercises.""Even though there are many dynamical systems books on the market, this book is bound to become a classic. The the
International Nuclear Information System (INIS)
Riess, R.
1980-01-01
The present paper describes the coolant chemistry and its consequences for 1300 MWsub(e) KWU PWR plants. Some selected systems, i.e. primary heat transport system, steam water cycle and cooling water arrangements, are chosen for this description. Various aspects of coolant chemistry regarding general corrosion, selective types of corrosion and deposits on heat transfer surfaces have been discussed. The water supply systems necessary to fulfill the requirements of the coolant chemistry are discussed as well. It has been concluded that a good operating performance can only be achieved when - beside other factors - the water chemistry has been given sufficient consideration. (orig./RW)
International Nuclear Information System (INIS)
Riess, R.
1981-01-01
The present paper describes the coolant chemistry and its consequences for 1300 MWsub(e) KWU PWR plants. Some selected systems, i.e. primary heat transport system, steam water cycle and cooling water arrangements, are chosen for this description. Various aspects of coolant chemistry regarding general corrosion, selective types of corrosion and deposits on heat transfer surface have been discussed. The water supply systems necessary to fulfill the requirements of the coolant chemistry are discussed as well. It has been concluded that a good operating performance can only be achieved when - beside other factors - the water chemistry has been given sufficient consideration. (orig./RW)
International Nuclear Information System (INIS)
Froggatt, R.J.
1981-01-01
The invention provides a two dimensional imaging system in which a pattern of radiation falling on the system is detected to give electrical signals for each of a plurality of strips across the pattern. The detection is repeated for different orientations of the strips and the whole processed by compensated back projection. For a shadow x-ray system a plurality of strip x-ray detectors are rotated on a turntable. For lower frequencies the pattern may be rotated with a Dove prism and the strips condensed to suit smaller detectors with a cylindrical lens. (author)
Directory of Open Access Journals (Sweden)
Oset E.
2012-12-01
Full Text Available I make a short review of the situation of the kaonic systems, with novel information supporting the two Λ(1405 states from the K-d → nπΣ reaction. A review is made of the K¯$ar K$NN system with recent calculations converging to smaller bindings and larger widths. Novel systems involving two kaons and one nucleon or three kaons are also reported and finally a short discussion is made of the analogous state DNN for which recent studies find a large binding and a small width.
PROFITABILITY OF THE CEE BANKING SYSTEMS DURING THE CRISIS PERIOD
Directory of Open Access Journals (Sweden)
MAGDALENA RADULESCU
2012-01-01
Full Text Available The increase of the foreign property in the CEE countries took place at the same time with the increase of the concentration on the banking market. The foreign countries contributed to the highest concentration level of the banking market through two channels: the acquisition by the foreign banks of some local institutions and the consolidation of the local (autochthonous institutions. Plus, the capital markets have developed considerably in the CEE countries, offering the firms alternative financing sources.
Directory of Open Access Journals (Sweden)
O. N. Faizulaieva
2014-09-01
Full Text Available Scientific task for improving the signal-to-noise ratio for user’s voice signal in computer systems and networks during the process of user’s voice authentication is considered. The object of study is the process of input and extraction of the voice signal of authentication system user in computer systems and networks. Methods and means for input and extraction of the voice signal on the background of external interference signals are investigated. Ways for quality improving of the user’s voice signal in systems of voice authentication are investigated experimentally. Firmware means for experimental unit of input and extraction of the user’s voice signal against external interference influence are considered. As modern computer means, including mobile, have two-channel audio card, two microphones are used in the voice signal input. The distance between sonic-wave sensors is 20 mm and it provides forming one direction pattern lobe of microphone array in a desired area of voice signal registration (from 100 Hz to 8 kHz. According to the results of experimental studies, the usage of directional properties of the proposed microphone array and space-time processing of the recorded signals with implementation of constant and adaptive weighting factors has made it possible to reduce considerably the influence of interference signals. The results of firmware experimental studies for input and extraction of the user’s voice signal against external interference influence are shown. The proposed solutions will give the possibility to improve the value of the signal/noise ratio of the useful signals recorded up to 20 dB under the influence of external interference signals in the frequency range from 4 to 8 kHz. The results may be useful to specialists working in the field of voice recognition and speaker discrimination.
The systems integration modeling system
International Nuclear Information System (INIS)
Danker, W.J.; Williams, J.R.
1990-01-01
This paper discusses the systems integration modeling system (SIMS), an analysis tool for the detailed evaluation of the structure and related performance of the Federal Waste Management System (FWMS) and its interface with waste generators. It's use for evaluations in support of system-level decisions as to FWMS configurations, the allocation, sizing, balancing and integration of functions among elements, and the establishment of system-preferred waste selection and sequencing methods and other operating strategies is presented. SIMS includes major analysis submodels which quantify the detailed characteristics of individual waste items, loaded casks and waste packages, simulate the detailed logistics of handling and processing discrete waste items and packages, and perform detailed cost evaluations
Nazihah Mat Daud, Anis; Jaafar, Rosly; Kadri Ayop, Shahrul; Supar Rohani, Md
2018-04-01
This paper discusses the development of a computerized acoustic characterization system of non-porous solid tissue mimicking materials. This system employs an alternative pulse echo immersion technique and consists of a pulser/receiver generator, a transducer used as both a transmitter and a receiver, a digital oscilloscope, and a personal computer with a custom-developed program installed. The program was developed on the LabVIEW 2012 platform and comprises two main components, a user interface and a block diagram. The user interface consists of three panels: a signal acquisition and selection panel, a display panel, and a calculation panel. The block diagram comprises four blocks: a signal acquisition block, a peak signal analysis block, an acoustic properties calculation and display block, and an additional block. Interestingly, the system can be operated in both online and offline modes. For the online mode, the measurements are performed by connecting the system with a Rigol DS2000 Series digital oscilloscope. In contrast, the measurements are carried out by processing the saved data on the computer for the offline mode. The accuracy and consistency of the developed system was validated by a KB-Aerotech Alpha Series transducer with 5 MHz center frequency and a Rigol DS2202 two-channel 200 MHz 2 GSa s-1 digital oscilloscope, based on the measurement of the acoustic properties of three poly(methyl methacrylate) samples immersed in a medium at a temperature of (24.0 ± 0.1) °C. The findings indicated that the accuracy and consistency of the developed system was exceptionally high, within a 1.04% margin of error compared to the reference values. As such, this computerized system can be efficiently used for the acoustic characterization of non-porous solid tissues, given its spontaneous display of results, user-friendly interface, and convenient hardware connection.
African Journals Online (AJOL)
1,3,2-DIAZABORACYCLOALKANE. RING SYSTEM. Negussie Retta" and Robert H. Neilson. 'Department of Chemistry, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia. Department of Chemistry, Texas Christian University.
The web site provides guidance and technical assistance for homeowners, government officials, industry professionals, and EPA partners about how to properly develop and manage individual onsite and community cluster systems that treat domestic wastewater.
Bartlett, R. G., Jr.
1973-01-01
The general anatomy and function of the human respiratory system is summarized. Breathing movements, control of breathing, lung volumes and capacities, mechanical relations, and factors relevant to respiratory support and equipment design are discussed.
Avdeev, Alexander A
2016-01-01
This monograph presents a systematic analysis of bubble system mathematics, using the mechanics of two-phase systems in non-equilibrium as the scope of analysis. The author introduces the thermodynamic foundations of bubble systems, ranging from the fundamental starting points to current research challenges. This book addresses a range of topics, including description methods of multi-phase systems, boundary and initial conditions as well as coupling requirements at the phase boundary. Moreover, it presents a detailed study of the basic problems of bubble dynamics in a liquid mass: growth (dynamically and thermally controlled), collapse, bubble pulsations, bubble rise and breakup. Special emphasis is placed on bubble dynamics in turbulent flows. The analysis results are used to write integral equations governing the rate of vapor generation (condensation) in non-equilibrium flows, thus creating a basis for solving a number of practical problems. This book is the first to present a comprehensive theory of boil...
Indian Academy of Sciences (India)
IAS Admin
study and understand the function of biological systems, particu- larly, the response of such .... understand the organisation and behaviour of prokaryotic sys- tems. ... relationship of the structure of a target molecule to its ability to bind a certain ...
DEFF Research Database (Denmark)
At first glance, this book may appear eclectic. It contains writings from architectural practice in a language and structure based on subjective views and experiences, combined with research contributions based on systematic design investigations of discrete computational systems. Discussions range......, and it aims to illustrate and identify new modes of working in architecture, particularly with regards to brickwork and other complex systems of modular assemblies, whether physical or digital....
Lucas, P.J.F.
2005-01-01
Expert systems mimic the problem-solving activity of human experts in specialized domains by capturing and representing expert knowledge. Expert systems include a knowledge base, an inference engine that derives conclusions from the knowledge, and a user interface. Knowledge may be stored as if-then rules, orusing other formalisms such as frames and predicate logic. Uncertain knowledge may be represented using certainty factors, Bayesian networks, Dempster-Shafer belief functions, or fuzzy se...
Directory of Open Access Journals (Sweden)
Lixin Dong
2008-11-01
Full Text Available Two strategies towards the realization of nanotechnology have been presented, i.e., top-down and bottom up. The former one is mainly based on nanofabrication and includes technologies such as nano-lithography, nano-imprint, and etching. Presently, they are still 2D fabrication processes with low resolution. The later one is an assembly-based technique. At present, it includes such items as self-assembly, dip-pen lithography, and directed self-assembly. These techniques can generate regular nano patterns in large scales. To fabricate 3D complex nano devices there are still no effective ways by so far. Here we show our effort on the development of a nano laboratory, a prototype nanomanufacturing system, based on nanorobotic manipulations. In which, we take a hybrid strategy as shown in Fig. 1. In this system, nano fabrication and nano assembly can be performed in an arbitrary order to construct nano building blocks and finally nano devices. The most important feature in this system is that the products can be fed back into the system to shrink the system part by part leading to nanorobots. Property characterization can be performed in each intermediate process. Due to the nanorobotic manipulation system, dynamic measurement can be performed rather than conventional static observations.
Fiscal system analysis - contractual systems
International Nuclear Information System (INIS)
Kaiser, M.J.
2006-01-01
Production sharing contracts are one of the most popular forms of contractual system used in petroleum agreements around the world, but the manner in which the fiscal terms and contract parameters impact system measures is complicated and not well understood. The purpose of this paper is to quantify the influence of private and market uncertainty in contractual fiscal systems. A meta-modelling approach is employed that couples the results of a simulation model with regression analysis to construct numerical functionals that quantify the fiscal regime. Relationships are derived that specify how the present value, rate of return, and take statistics vary as a function of the system parameters. The deepwater Girassol field development in Angola is taken as a case study. (author)
International Nuclear Information System (INIS)
Miyano, Hiroshi; Narabayashi, Naoshi.
1990-01-01
The represent invention concerns a reactor system with improved water injection means to a pressure vessel of a BWR type reactor. A steam pump is connected to a heat removing system pipeline, a high pressure water injection system pipeline and a low pressure water injection system pipeline for injecting water into the pressure vessel. A pump actuation pipeline is disposed being branched from a main steam pump or a steam relieaf pipeline system, through which steams are supplied to actuate the steam pump and supply cooling water into the pressure vessel thereby cooling the reactor core. The steam pump converts the heat energy into the kinetic energy and elevates the pressure of water to a level higher than the pressure of the steams supplied by way of a pressure-elevating diffuser. Cooling water can be supplied to the pressure vessel by the pressure elevation. This can surely inject cooling water into the pressure vessel upon loss of coolant accident or in a case if reactor scram is necessary, without using an additional power source. (I.N.)
International Nuclear Information System (INIS)
Kelly, M.F.; Wyman, R.H.
1975-01-01
In spite of the remarkable safety record of the nuclear industry as a whole, recent public concern over the potential impact of the industry's accelerated growth has prompted ERDA to expand its emergency response procedures. The Atmospheric Release Advisory Capability, ARAC, is a computer communications system designed to enhance the existing emergency response capability of ERDA nuclear facilities. ARAC will add at least two new functions to this capability: centralized, real-time data acquisition and storage, and simulation of the long range atmospheric transport of hazardous materials. To perform these functions, ARAC employs four major sub-systems or facilities: the site facility, the central facility, the global weather center and the regional model. The system has been under development for the past two years at the Lawrence Livermore Laboratory of the University of California