Superconductivity of composite particles in a two-channel Kondo lattice.
Hoshino, Shintaro; Kuramoto, Yoshio
2014-04-25
Emergence of odd-frequency s-wave superconductivity is demonstrated in the two-channel Kondo lattice by means of the dynamical mean-field theory combined with the continuous-time quantum Monte Carlo method. Around half filling of the conduction bands, divergence of an odd-frequency pairing susceptibility is found, which signals instability toward the superconductivity. The corresponding order parameter is equivalent to a staggered composite-pair amplitude with even frequencies, which involves both localized spins and conduction electrons. A model wave function is constructed for the composite order with the use of symmetry operations such as charge conjugation and channel rotations. Given a certain asymmetry of the conduction bands, another s-wave superconductivity is found that has a uniform order parameter. The Kondo effect in the presence of two channels is essential for both types of unconventional superconductivity.
Correlations between Kondo clouds in nearly antiferromagnetic Kondo lattices
Energy Technology Data Exchange (ETDEWEB)
Kiselev, M.N. E-mail: kiselev@physik.uni-wuerzburg.de; Kikoin, K.A
2004-05-01
We discuss a novel fluctuational mechanism explaining the physics of nearly antiferromagnetic Kondo lattices (KL). The effective action for KL model is expressed in terms of Bose operators responsible for paramagnetic excitations and semi-bosonic fields describing the dynamic Kondo clouds created by conduction electrons around local spin. The gauge invariant resonance valence bond theory of interacting Kondo clouds describes the spin liquid with strong critical fluctuations imitating itinerant fluctuation magnetism of Moriya type.
From four- to two-channel Kondo effect in junctions of XY spin chains
Directory of Open Access Journals (Sweden)
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
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.
Two-channel Kondo effect and renormalization flow with macroscopic quantum charge states.
Iftikhar, Z; Jezouin, S; Anthore, A; Gennser, U; Parmentier, F D; Cavanna, A; Pierre, F
2015-10-08
Many-body correlations and macroscopic quantum behaviours are fascinating condensed matter problems. A powerful test-bed for the many-body concepts and methods is the Kondo effect, which entails the coupling of a quantum impurity to a continuum of states. It is central in highly correlated systems and can be explored with tunable nanostructures. Although Kondo physics is usually associated with the hybridization of itinerant electrons with microscopic magnetic moments, theory predicts that it can arise whenever degenerate quantum states are coupled to a continuum. Here we demonstrate the previously elusive 'charge' Kondo effect in a hybrid metal-semiconductor implementation of a single-electron transistor, with a quantum pseudospin of 1/2 constituted by two degenerate macroscopic charge states of a metallic island. In contrast to other Kondo nanostructures, each conduction channel connecting the island to an electrode constitutes a distinct and fully tunable Kondo channel, thereby providing unprecedented access to the two-channel Kondo effect and a clear path to multi-channel Kondo physics. Using a weakly coupled probe, we find the renormalization flow, as temperature is reduced, of two Kondo channels competing to screen the charge pseudospin. This provides a direct view of how the predicted quantum phase transition develops across the symmetric quantum critical point. Detuning the pseudospin away from degeneracy, we demonstrate, on a fully characterized device, quantitative agreement with the predictions for the finite-temperature crossover from quantum criticality.
Instability of Non-Fermi Liquid Behavior in the Two-Channel Kondo Model
Institute of Scientific and Technical Information of China (English)
YUAN Qing-Shan; CHEN Hong; ZHANG Yu-Mei
2001-01-01
The effects of interchannel scattering of conduction electrons by the impu rity and repulsion of conduction electrons at the impurity site on the two-channel Kondo model are simultaneously considered in this paper.It is shown that these two perturbations will substantially modify the usual local non-Fermi liquid behavior of the two-channel Kondo model.With bosonization and unitary transformations we find that the system can be transformed into a single channel Kondo model with anisotropy between longitudinal and transverse exchange couplings.Whatever for originally antiferromagnetic or ferromagnetic isotropic coupling,the system always flows to strong-coupling limit,which exhibits local Fermi liquid behavior at low temperatures.
Universality and scaling in a charge two-channel Kondo device
Mitchell, Andrew K.; Landau, L. A.; Fritz, L.; Sela, E.
2016-01-01
We study a charge two-channel Kondo model, demonstrating that recent experiments [Iftikhar et al, Nature 526, 233 (2015)] realize an essentially perfect quantum simulation -- not just of its universal physics, but also nonuniversal effects away from the scaling limit. Numerical renormalization group
Anisotropic Kondo lattice without Nozieres exhaustion effect
Energy Technology Data Exchange (ETDEWEB)
Kiselev, M.N. [Physics Department, Arnold Sommerfeld Center for Theoretical Physics and Center for Nano-Science, Ludwig-Maximilians Universitaet Muenchen, 80333 Munich (Germany)]. E-mail: kiselev@physik.uni-wuerzburg.de; Kikoin, K. [Ben-Gurion University of the Negev, Beer-Sheva, 84105 (Israel)]. E-mail: kikoin@bgumail.bgu.ac.il
2006-05-01
The properties of layered Anderson/Kondo lattices with metallic electrons confined in 2D xy planes and local spins in insulating layers forming chains in z direction are studied. Each spin possesses its own 2D Kondo cloud, so that the Nozieres' exhaustion problem does not arise. The excitation spectrum is gapless both in charge and spin sectors. Possible experimental realizations of the model are briefly discussed.
Kondo lattice without Nozieres exhaustion effect.
Energy Technology Data Exchange (ETDEWEB)
Kikoin, K.; Kiselev, M. N.; Materials Science Division; Ben-Gurion Univ. of the Negev; Ludwig-Maximilians Univ.
2006-01-01
We discuss the properties of layered Anderson/Kondo lattices with metallic electrons confined in 2D xy planes and local spins in insulating layers forming chains in the z direction. Each spin in this model possesses its own 2D Kondo cloud, so that the Nozieres exhaustion problem does not occur. The high-temperature perturbational description is matched to exact low-T Bethe-ansatz solution. The excitation spectrum of the model is gapless both in charge and spin sectors. The disordered phases and possible experimental realizations of the model are briefly discussed.
Superconductivity in the Kondo lattice model
Energy Technology Data Exchange (ETDEWEB)
Bodensiek, Oliver; Pruschke, Thomas [Institute for Theoretical Physics, University of Goettingen, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Zitko, Rok [Institute for Theoretical Physics, University of Goettingen, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana (Slovenia)
2011-07-01
We study the Kondo lattice model with an additional attractive interaction among the conduction-band electrons by means of dynamical mean-field theory in combination with the numerical renormalization group method. In the normal phase we observe a strong dependency of the low-energy scale on the attractive interaction. Thus, there exists a delicate interplay between the attractive interaction and the antiferromagnetic Kondo exchange, which results in a critical interaction, above of which the Fermi surface collapses because the spins become effectively decoupled from the conduction electrons. Additionally, we allow for a s-wave superconducting phase, which appears to be split at the point of the underlying Fermi surface collapse. We discuss the interplay between attractive interaction an Kondo exchange and its pertinence to phonons in heavy fermion physics.
Two-channel Kondo effect and the low-temperature crossover
Keller, Andrew; Peeters, Lucas; Weymann, Ireneusz; Moca, Cătălin Paşcu; Mahalu, Diana; Umansky, Vladimir; Zaránd, Gergely; Goldhaber-Gordon, David
2015-03-01
The two-channel Kondo (2CK) state, where a spin-1/2 impurity is equally exchange-coupled to two independent reservoirs, is a canonical non-Fermi liquid state. Experimental observations are rare because of its sensitivity to common and hard-to-control perturbations. We implement experimentally a 2CK state in a coupled dot-grain system (Potok, et al., doi:10.1038/nature05556), and explore the physics of the low-temperature crossover: how magnetic field and gate voltage drive the system towards a Fermi liquid ground state. Our experimental findings are corroborated by detailed numerical renormalization group modeling of our device.
The Correlated Kondo-lattice Model
Kienert, J.; Santos, C.; Nolting, W.
2003-01-01
We investigate the ferromagnetic Kondo-lattice model (FKLM) with a correlated conduction band. A moment conserving approach is proposed to determine the electronic self-energy. Mapping the interaction onto an effective Heisenberg model we calculate the ordering of the localized spin system self-consistently. Quasiparticle densities of states (QDOS) and the Curie temperature are calculated. The band interaction leads to an upper Hubbard peak and modifies the magnetic stability of the FKLM.
Spin Relaxation in Kondo Lattice Systems with Anisotropic Kondo Interaction
Belov, S. I.; Kutuzov, A. S.
2016-12-01
We study the influence of the Kondo effect on the spin relaxation in systems with anisotropic Kondo interaction at temperatures both high and low as compared with the static magnetic field. In the absence of the Kondo effect, the electron spin resonance linewidth is not narrowed in the whole temperature range due to the high anisotropy of the Kondo interaction. The Kondo effect leads to the universal energy scale, which regulates the temperature and magnetic field dependence of different kinetic coefficients and results in a mutual cancelation of their singular parts in a collective spin mode.
Universal low-temperature crossover in two-channel Kondo models
Mitchell, Andrew K.; Sela, Eran
2012-06-01
An exact expression is derived for the electron Green function in two-channel Kondo models with one and two impurities, describing the crossover from non-Fermi liquid (NFL) behavior at intermediate temperatures to standard Fermi liquid (FL) physics at low temperatures. Symmetry-breaking perturbations generically present in experiment ensure the standard low-energy FL description, but the full crossover is wholly characteristic of the unstable NFL state. Distinctive conductance lineshapes in quantum dot devices should result. We exploit a connection between this crossover and one occurring in a classical boundary Ising model to calculate real-space electron densities at finite temperature. The single universal finite-temperature Green function is then extracted by inverting the integral transformation relating these Friedel oscillations to the t matrix. Excellent agreement is demonstrated between exact results and full numerical renormalization group calculations.
Kondo Destruction in RKKY-Coupled Kondo Lattice and Multi-Impurity Systems
Nejati, Ammar; Ballmann, Katinka; Kroha, Johann
2017-03-01
In a Kondo lattice, the spin exchange coupling between a local spin and the conduction electrons acquires nonlocal contributions due to conduction electron scattering from surrounding local spins and the subsequent RKKY interaction. It leads to a hitherto unrecognized interference of Kondo screening and the RKKY interaction beyond the Doniach scenario. We develop a renormalization group theory for the RKKY-modified Kondo vertex. The Kondo temperature TK(y ) is suppressed in a universal way, controlled by the dimensionless RKKY coupling parameter y . Complete spin screening ceases to exist beyond a critical RKKY strength yc even in the absence of magnetic ordering. At this breakdown point, TK(y ) remains nonzero and is not defined for larger RKKY couplings y >yc. The results are in quantitative agreement with STM spectroscopy experiments on tunable two-impurity Kondo systems. The possible implications for quantum critical scenarios in heavy-fermion systems are discussed.
Observation of orbital two-channel Kondo effect in a ferromagnetic L10-MnGa film
Zhu, Lijun; Woltersdorf, Georg; Zhao, Jianhua
2016-09-01
The experimental existence and stability of the fixed point of the two-channel Kondo (2CK) effect displaying exotic non-Fermi liquid physics have been buried in persistent confusion despite the intensive theoretical and experimental efforts in past three decades. Here we report an experimental realization of the two-level system resonant scattering-induced orbital 2CK effect in a ferromagnetic L10-MnGa film, which is signified by a magnetic field-independent resistivity upturn that has a logarithmic and a square-root temperature dependence beyond and below the Kondo temperature of ~14.5 K, respectively. Our results not only evidence the robust existence of orbital 2CK effect even in the presence of strong magnetic fields and long-range ferromagnetic ordering, but also extend the scope of 2CK host materials from nonmagnetic nanoscale point contacts to diffusive conductors of disordered alloys.
Spiral Magnetic Order in the One-Dimensional Kondo Lattice
Institute of Scientific and Technical Information of China (English)
LIU Zhen-Rong; LI Zheng-Zhong; SHEN Rui
2001-01-01
The effects of c-f (conduction-f electrons) hybridization on the spiral spin magnetism in the one dimensional Kondo lattice are studied. By using the mean-field approximation, a close set of equations of the Green's functions with arbitrary wave vector Q for the spiral ordering of spins is deduced. The magnetic phase boundary between the spiral magnetism and ferromagnetism has been calculated approximately. From our qualitative results, one can find that the ferromagnetic region is enlarged due to the c f hybridization. Moreover, some new results reflecting the Kondo effect, such as the modified dispersion relation and the weakening of the localized magnetic moments are also obtained.
Anomalous Hall effect in L 10-MnAl films with controllable orbital two-channel Kondo effect
Zhu, L. J.; Nie, S. H.; Zhao, J. H.
2016-05-01
The anomalous Hall effect (AHE) in strongly disordered magnetic systems has been buried in persistent confusion despite its long history. We report the AHE in perpendicularly magnetized L 10-MnAl epitaxial films with a variable orbital two-channel Kondo (2CK) effect arising from the strong coupling of conduction electrons and the structural disorders of two-level systems. The AHE is observed to excellently scale with ρAH/f =a0ρx x 0+b ρxx 2 at high temperatures where phonon scattering prevails. In contrast, significant deviation occurs at low temperatures where the orbital 2CK effect becomes important, suggesting a negative AHE contribution. The deviation of the scaling agrees with the orbital 2CK effect in the breakdown temperatures and deviation magnitudes.
Toward a new microscopic framework for Kondo lattice materials
Lonzarich, Gilbert; Pines, David; Yang, Yi-feng
2017-02-01
Understanding the emergence and subsequent behavior of heavy electrons in Kondo lattice materials is one of the grand challenges in condensed matter physics. From this perspective we review the progress that has been made during the past decade and suggest some directions for future research. Our focus will be on developing a new microscopic framework that incorporates the basic concepts that emerge from a phenomenological description of the key experimental findings.
The strong coupling Kondo lattice model as a Fermi gas
Östlund, S
2007-01-01
The strong coupling half-filled Kondo lattice model is an important example of a strongly interacting dense Fermi system for which conventional Fermi gas analysis has thus far failed. We remedy this by deriving an exact transformation that maps the model to a dilute gas of weakly interacting electron and hole quasiparticles that can then be analyzed by conventional dilute Fermi gas methods. The quasiparticle vacuum is a singlet Mott insulator for which the quasiparticle dynamics are simple. Since the transformation is exact, the electron spectral weight sum rules are obeyed exactly. Subtleties in understanding the behavior of electrons in the singlet Mott insulator can be reduced to a fairly complicated but precise relation between quasiparticles and bare electrons. The theory of free quasiparticles can be interpreted as an exactly solvable model for a singlet Mott insulator, providing an exact model in which to explore the strong coupling regime of a singlet Kondo insulator.
Ground-state phase diagram of the Kondo lattice model on triangular-to-kagome lattices
Akagi, Yutaka; Motome, Yukitoshi
2012-01-01
We investigate the ground-state phase diagram of the Kondo lattice model with classical localized spins on triangular-to-kagome lattices by using a variational calculation. We identify the parameter regions where a four-sublattice noncoplanar order is stable with a finite spin scalar chirality while changing the lattice structure from triangular to kagome continuously. Although the noncoplanar spin states appear in a wide range of parameters, the spin configurations on the kagome network beco...
Critical quasiparticles in single-impurity and lattice Kondo models
Vojta, M.; Bulla, R.; Wölfle, P.
2015-07-01
Quantum criticality in systems of local moments interacting with itinerant electrons has become an important and diverse field of research. Here we review recent results which concern (a) quantum phase transitions in single-impurity Kondo and Anderson models and (b) quantum phase transitions in heavy-fermion lattice models which involve critical quasiparticles. For (a) the focus will be on impurity models with a pseudogapped host density of states and their applications, e.g., in graphene and other Dirac materials, while (b) is devoted to strong-coupling behavior near antiferromagnetic quantum phase transitions, with potential applications in a variety of heavy-fermion metals.
Superconductivity of heavy fermions in the Kondo lattice model
Energy Technology Data Exchange (ETDEWEB)
Sykora, Steffen [IFW Dresden (Germany); Becker, Klaus W. [Institut fuer Theoretische Physik, Technische Universitaet Dresden (Germany)
2015-07-01
Understanding of the origin of superconductivity in strongly correlated electron systems is one of the basic unresolved problems in physics. Examples for such systems are the cuprates and also the heavy-fermion metals, which are compounds with 4f and 5f electrons. In all these materials the superconducting pairing interaction is often believed to be predominantly mediated by spin fluctuations and not by phonons as in normal metals. For the Kondo-lattice model we present results, which are derived within the Projective Renormalization Method (PRM). Based on a recent study of the one-particle spectral function for the normal state we first derive an effective Hamiltonian which describes heavy fermion quasiparticle bands close to the Fermi surface. An extension to the superconducting phase leads to d-wave solutions for the superconducting order parameter in agreement with recent STM measurements.
Arnold, Michael; Langenbruch, Tobias; Kroha, Johann
2007-11-02
We propose a physical realization of the two-channel Kondo (2CK) effect, where a dynamical defect in a metal has a unique ground state and twofold degenerate excited states. In a wide range of parameters the interactions with the electrons renormalize the excited doublet downward below the bare defect ground state, thus stabilizing the 2CK fixed point. In addition to the Kondo temperature T(K) the three-state defect exhibits another low-energy scale, associated with ground-to-excited-state transitions, which can be exponentially smaller than T(K). Using the perturbative nonequilibrium renormalization group we demonstrate that this can provide the long-sought explanation of the sharp conductance spikes observed by Ralph and Buhrman in ultrasmall metallic point contacts.
Emergence of a Fermionic Finite-Temperature Critical Point in a Kondo Lattice.
Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Mou, Chung-Yu; Lee, Ting-Kuo
2016-04-29
The underlying Dirac point is central to the profound physics manifested in a wide class of materials. However, it is often difficult to drive a system with Dirac points across the massless fermionic critical point. Here by exploiting screening of local moments under spin-orbit interactions in a Kondo lattice, we show that below the Kondo temperature, the Kondo lattice undergoes a topological transition from a strong topological insulator to a weak topological insulator at a finite temperature T_{D}. At T_{D}, massless Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our analysis indicates that the emergent relativistic symmetry dictates nontrivial thermal responses over large parameter and temperature regimes. In particular, it yields critical scaling behaviors both in magnetic and transport responses near T_{D}.
Spin-flux phase in the Kondo lattice model with classical localized spins
Agterberg, DF; Yunoki, S
2000-01-01
We provide numerical evidence that a spin-flux phase exists as a ground state of the Kondo lattice model with classical local spins on a square lattice. This state manifests itself as a double-e magnetic order in the classical spins with spin density at both (0, pi) and (pi ,0) and further exhibits
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.
Zero-temperature magnetic transition in an easy-axis Kondo lattice model.
Zhu, Jian-Xin; Kirchner, Stefan; Bulla, Ralf; Si, Qimiao
2007-11-30
We address the quantum transition of a spin-1/2 antiferromagnetic Kondo lattice model with an easy-axis anisotropy using the extended dynamical mean field theory. We derive results in real frequency by using the bosonic numerical renormalization group (BNRG) method and compare them with quantum Monte Carlo results in Matsubara frequency. The BNRG results show a logarithmic divergence in the critical local spin susceptibility, signaling a destruction of Kondo screening. The T=0 transition is consistent with being second order. The BNRG results also display some subtle features; we identify their origin and suggest means for further microscopic studies.
Zero-Temperature Magnetic Transition in an Easy-Axis Kondo Lattice Model
Zhu, Jian-Xin; Kirchner, Stefan; Bulla, Ralf; Si, Qimiao
2007-11-01
We address the quantum transition of a spin-1/2 antiferromagnetic Kondo lattice model with an easy-axis anisotropy using the extended dynamical mean field theory. We derive results in real frequency by using the bosonic numerical renormalization group (BNRG) method and compare them with quantum Monte Carlo results in Matsubara frequency. The BNRG results show a logarithmic divergence in the critical local spin susceptibility, signaling a destruction of Kondo screening. The T=0 transition is consistent with being second order. The BNRG results also display some subtle features; we identify their origin and suggest means for further microscopic studies.
Ferromagnetism in the Kondo-lattice compound CePd2P2.
Tran, Vinh Hung; Bukowski, Zbigniew
2014-06-25
We report physical properties of CePd2P2 crystallizing in the tetragonal ThCr2Si2-type structure (space group I4/mmm). Dc-magnetic susceptibility, magnetization, specific heat, electrical resistivity and magnetoresistance measurements establish a ferromagnetic ordering below the Curie temperature TC = 28.4 ± 0.2 K. Critical analysis of isothermal and isofield magnetization yields critical exponents of β = 0.405 ± 0.005, γ = 1.11 ± 0.05 and δ = 3.74 ± 0.04. The ordered state is characterized by saturation moment Ms ∼ 0.98μB and magnon energy gap Δ/kB ∼25–35 K. The studied properties reflect a competing influence of the Kondo and crystalline electric field (CEF) interactions. The strength of the Kondo effect is assigned by a low-temperature Kondo scale TK ∼19 ± 10 K and a high-temperature Kondo scale TK ~ H 117 } 10 K. A model of the inelastic scattering of the conduction electrons with an exchanged CEF energy ΔCEF was applied to the magnetic resistivity. An average value ΔCEF = 260 ± 30 K is consistent in the relationships with TK and TK H. We argue that the CePd2P2 compound appears to be a new ferromagnetic Kondo-lattice among the Ce-based intermetallics.
Two-Channel Kondo Physics due to As Vacancies in the Layered Compound ZrAs1.58 Se0.39
Cichorek, T.; Bochenek, L.; Schmidt, M.; Czulucki, A.; Auffermann, G.; Kniep, R.; Niewa, R.; Steglich, F.; Kirchner, S.
2016-09-01
We address the origin of the magnetic-field-independent -|A |T1 /2 term observed in the low-temperature resistivity of several As-based metallic systems of the PbFCl structure type. For the layered compound ZrAs1.58 Se0.39 , 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 nonmagnetic 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 ZrAs1.58 Se0.39 compared to the free-of-vacancies homologue ZrP1.54 S0.46 (Tc≈3.7 K ). Our findings should be relevant to a wide class of metals with disordered pnictogen layers.
Magnetic ordering and non-Fermi-liquid behavior in the multichannel Kondo-lattice model
Irkhin, Valentin Yu.
2016-05-01
Scaling equations for the Kondo lattice in the paramagnetic and magnetically ordered phases are derived to next-leading order with account of spin dynamics. The results are applied to describe various mechanisms of the non-Fermi-liquid (NFL) behavior in the multichannel Kondo-lattice model where a fixed point occurs in the weak-coupling region. The corresponding temperature dependences of electronic and magnetic properties are discussed. The model describes naturally formation of a magnetic state with soft boson mode and small moment value. An important role of Van Hove singularities in the magnon spectral function is demonstrated. The results are rather sensitive to the type of magnetic ordering and space dimensionality, the conditions for NFL behavior being more favorable in the antiferromagnetic and 2D cases.
Spiral magnetic phases on the Kondo Lattice Model: A Hartree-Fock approach
Costa, N. C.; Lima, J. P.; dos Santos, Raimundo R.
2017-02-01
We study the Kondo Lattice Model (KLM) on a square lattice through a Hartree-Fock approximation in which the local spins are treated semi-classically, in the sense that their average values are modulated by a magnetic wavevector Q while they couple with the conduction electrons through fermion operators. In this way, we obtain a ground state phase diagram in which spiral magnetic phases (in which the wavevector depends on the coupling constants and on the density) interpolate between the low-density ferromagnetic phase and the antiferromagnetic phase at half filling; within small regions of the phase diagram commensurate magnetic phases can coexist with Kondo screening. We have also obtained 'Doniach-like' diagrams, showing the effect of temperature on the ground state phases, and established that for some ranges of the model parameters (the exchange coupling and conduction electron density) the magnetic wavevector changes with temperature, either continuously or abruptly (e.g., from spiral to ferromagnetic).
Unusual phonon softening in the Kondo lattice CeCu 2
Loewenhaupt, Michael; Witte, Ulrike; Kramp, Sirko; Braden, Markus; Svoboda, Pavel
2002-03-01
CeCu2 is a Kondo lattice with antiferromagnetic order below 3.5 K and a Kondo temperature of about 6 K. Earlier neutron scattering experiments lead to the assumption of a coupling between a crystal field transition and some phonons with energies around 14 meV. With the results from our newly performed inelastic neutron measurements on a single crystal we found these assumptions confirmed. We observed an unusual softening of certain phonons with increasing temperature. This softening of up to 15% is much stronger than the normal thermal behavior of phonons. Additionally, the line width of these phonons is increasing. At the same time the magnetic response is strongly broadened by the coupling to the phonons. The findings for CeCu2 are discussed in relation with similar observation of a coupling between electronic and lattice degrees of freedom in CeAl2 and YbPO4.
Magnetic Quantum Phase Transitions of a Kondo Lattice Model with Ising Anisotropy
Zhu, Jian-Xin; Kirchner, Stefan; Si, Qimiao; Grempel, Daniel R.; Bulla, Ralf
2006-03-01
We study the Kondo Lattice model with Ising anisotropy, within an extended dynamical mean field theory (EDMFT) in the presence or absence of antiferromagnetic ordering. The EDMFT equations are studied using both the Quantum Monte Carlo (QMC) and Numerical Renormalization Group (NRG) methods. We discuss the overall magnetic phase diagram by studying the evolution, as a function of the ratio of the RKKY interaction and bare Kondo scale, of the local spin susceptibility, magnetic order parameter, and the effective Curie constant of a nominally paramagnetic solution with a finite moment. We show that, within the numerical accuracy, the quantum magnetic transition is second order. The local quantum critical aspect of the transition is also discussed.
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.
Developing Kondo lattice coherence and quantum criticality in YbRh{sub 2}Si{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Wirth, Steffen; Seiro, Silvia; Geibel, Christoph; Steglich, Frank [MPI for Chemical Physics of Solids, Dresden (Germany); Kirchner, Stefan [MPI for Physics of Complex Systems, Dresden (Germany); Krellner, Cornelius [Goethe University Frankfurt (Germany); Si, Qimiao [Rice University, Houston, Texas (United States)
2015-07-01
Hybridization is a fundamental concept in strongly correlated electron physics. In heavy fermion metals, it may result in the generation of low-energy scales that can give rise to quantum criticality and unconventional superconductivity. An important techniques that helped shaping our understanding of nonlocal correlations - magnetic and superconducting - has been tunneling spectroscopy (STS) with its unique ability to give local, microscopic information that directly relates to the one-particle Green's function. We investigated YbRh{sub 2}Si{sub 2}, an archetypal heavy fermion metal. Quantum criticality is discussed in terms of an antiferromagnetic instability and a Kondo break-down of the heavy quasiparticles. STS studies identified a hybridization-induced gap-like feature of the tunneling conductance. Here we focus on the evolution of the Kondo lattice. While the Kondo lattice starts forming already at the single-ion Kondo temperature, lattice Kondo effects dominate only at much lower temperatures. This establishes a hierarchy of energy scales. Finite-temperature signatures of the QCP are observed in field-dependent STS. Our findings are augmented by band structure calculations and transport measurements.
Long-range ferrimagnetic order in a two-dimensional supramolecular Kondo lattice
Girovsky, Jan; Nowakowski, Jan; Ali, Md. Ehesan; Baljozovic, Milos; Rossmann, Harald R.; Nijs, Thomas; Aeby, Elise A.; Nowakowska, Sylwia; Siewert, Dorota; Srivastava, Gitika; Wäckerlin, Christian; Dreiser, Jan; Decurtins, Silvio; Liu, Shi-Xia; Oppeneer, Peter M.; Jung, Thomas A.; Ballav, Nirmalya
2017-05-01
Realization of long-range magnetic order in surface-supported two-dimensional systems has been challenging, mainly due to the competition between fundamental magnetic interactions as the short-range Kondo effect and spin-stabilizing magnetic exchange interactions. Spin-bearing molecules on conducting substrates represent a rich platform to investigate the interplay of these fundamental magnetic interactions. Here we demonstrate the direct observation of long-range ferrimagnetic order emerging in a two-dimensional supramolecular Kondo lattice. The lattice consists of paramagnetic hexadeca-fluorinated iron phthalocyanine (FeFPc) and manganese phthalocyanine (MnPc) molecules co-assembled into a checkerboard pattern on single-crystalline Au(111) substrates. Remarkably, the remanent magnetic moments are oriented in the out-of-plane direction with significant contribution from orbital moments. First-principles calculations reveal that the FeFPc-MnPc antiferromagnetic nearest-neighbour coupling is mediated by the Ruderman-Kittel-Kasuya-Yosida exchange interaction via the Au substrate electronic states. Our findings suggest the use of molecular frameworks to engineer novel low-dimensional magnetically ordered materials and their application in molecular quantum devices.
Long-range ferrimagnetic order in a two-dimensional supramolecular Kondo lattice.
Girovsky, Jan; Nowakowski, Jan; Ali, Md Ehesan; Baljozovic, Milos; Rossmann, Harald R; Nijs, Thomas; Aeby, Elise A; Nowakowska, Sylwia; Siewert, Dorota; Srivastava, Gitika; Wäckerlin, Christian; Dreiser, Jan; Decurtins, Silvio; Liu, Shi-Xia; Oppeneer, Peter M; Jung, Thomas A; Ballav, Nirmalya
2017-05-22
Realization of long-range magnetic order in surface-supported two-dimensional systems has been challenging, mainly due to the competition between fundamental magnetic interactions as the short-range Kondo effect and spin-stabilizing magnetic exchange interactions. Spin-bearing molecules on conducting substrates represent a rich platform to investigate the interplay of these fundamental magnetic interactions. Here we demonstrate the direct observation of long-range ferrimagnetic order emerging in a two-dimensional supramolecular Kondo lattice. The lattice consists of paramagnetic hexadeca-fluorinated iron phthalocyanine (FeFPc) and manganese phthalocyanine (MnPc) molecules co-assembled into a checkerboard pattern on single-crystalline Au(111) substrates. Remarkably, the remanent magnetic moments are oriented in the out-of-plane direction with significant contribution from orbital moments. First-principles calculations reveal that the FeFPc-MnPc antiferromagnetic nearest-neighbour coupling is mediated by the Ruderman-Kittel-Kasuya-Yosida exchange interaction via the Au substrate electronic states. Our findings suggest the use of molecular frameworks to engineer novel low-dimensional magnetically ordered materials and their application in molecular quantum devices.
4 f excitations in Ce Kondo lattices studied by resonant inelastic x-ray scattering
Amorese, A.; Dellea, G.; Fanciulli, M.; Seiro, S.; Geibel, C.; Krellner, C.; Makarova, I. P.; Braicovich, L.; Ghiringhelli, G.; Vyalikh, D. V.; Brookes, N. B.; Kummer, K.
2016-04-01
The potential of resonant inelastic soft x-ray scattering to measure 4 f crystal electric-field excitation spectra in Ce Kondo lattices has been examined. Spectra have been obtained for several Ce systems and show a well-defined structure determined by crystal-field, spin-orbit, and charge-transfer excitations only. The spectral shapes of the excitation spectra can be well understood in the framework of atomic multiplet calculations. For CeCu2Si2 we found notable disagreement between the inelastic x-ray-scattering spectra and theoretical calculations when using the crystal-field scheme proposed from inelastic neutron scattering. Modified sets of crystal-field parameters yield better agreement. Our results also show that, with the very recent improvements of soft x-ray spectrometers in resolution to below 30 meV at the Ce M4 ,5 edges, resonant inelastic x-ray scattering could be an ideal tool to determine the crystal-field scheme in Ce Kondo lattices and other rare-earth compounds.
Zero-Temperature Magnetic Transition in an Easy-Axis Kondo Lattice Model --- An NRG Study
Zhu, Jian-Xin; Kirchner, Stefan; Bulla, Ralf; Si, Qimiao
2007-03-01
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. Here we address the quantum transition of a spin-12 antiferromagnetic Kondo lattice model with an easy-axis anisotropy within the extended dynamical mean field theory. We derive results [1] in real frequency using the bosonic numerical renormalization group (bNRG) method and compare them with Quantum Monte Carlo results in Matsubara frequency. The bNRG results show a logarithmic divergence in the critical local spin susceptibility, signaling a destruction of Kondo screening. The T=0 transition is nearly second order, with any jump in the magnetic order parameter not exceeding a few percents of the full moment. The bNRG results also display some subtle features; we discuss their possible origins and suggest means for further microscopic studies. [1] J.-X. Zhu, S. Kirchner, R. Bulla, and Q. Si, cond-mat/0607567.
Crystal field-phonon coupling in the Kondo lattice CeCu2
Witte, U.; Kramp, S.; Braden, M.; Svoboda, P.; Loewenhaupt, M.
CeCu2 is a Kondo lattice and shows antiferromagnetic order below 3.5K. In earlier neutron-scattering experiments on a polycrystalline sample an anomaly in the inelastic neutron spectra at about 14 meV and at temperatures between 100 and 150K was observed. This has led to the assumption of a coupling between a crystal field transition between two excited levels and phonons. Inelastic neutron measurements on a single crystal confirm this assumption. We find an unusual strong energy shift (up to 15%) of certain phonons with increasing temperature, depending on their symmetry. At the same time the magnetic response is strongly broadened due to the coupling to the phonons.
Crystal field-phonon coupling in the Kondo lattice CeCu{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Witte, U. [TU Dresden, Institut fuer Angewandte Physik (IAPD), 01062 Dresden (Germany); HMI Berlin, Glienicker Str. 100, 14109 Berlin (Germany); Kramp, S. [HMI Berlin, Glienicker Str. 100, 14109 Berlin (Germany); Braden, M. [LLB Saclay, 91191 Gif-Sur-Yvette Cedex (France); Svoboda, P. [Charles University, 12116 Praha (Czech Republic); Loewenhaupt, M. [TU Dresden, Institut fuer Angewandte Physik (IAPD), 01062 Dresden (Germany)
2002-07-01
CeCu{sub 2} is a Kondo lattice and shows antiferromagnetic order below 3.5 K. In earlier neutron-scattering experiments on a polycrystalline sample an anomaly in the inelastic neutron spectra at about 14 meV and at temperatures between 100 and 150 K was observed. This has led to the assumption of a coupling between a crystal field transition between two excited levels and phonons. Inelastic neutron measurements on a single crystal confirm this assumption. We find an unusual strong energy shift (up to 15%) of certain phonons with increasing temperature, depending on their symmetry. At the same time the magnetic response is strongly broadened due to the coupling to the phonons. (orig.)
STEM in Kondo Lattices: a new window on correlated electron materials
Coleman, Piers
2012-02-01
The tremendous developments in scanning tunneling electron spectroscopy over the past decade, applied with tremendous success to the cuprate superconductors, are now beginning to be applied to other strongly correlated electron systems. One area where they offer tremendous potential, is in the context of heavy fermion materials. In the last few years, it has become possible to start probing the physics of the Kondo lattice using STEM methods. In this talk I will review this field, discussing the physics of tunneling into the Kondo lattice, showing how tunneling involves a co-operative process of electron transfer and spin-flip, called ``cotunnelling'' [1,2]. I will provide an overview of latest results in this field, especially URu2Si2 [3,4], YbRh2Si2 [5] and CeCoIn5 [6], discussing how STEM can be used to probe various new theoretical proposals [7,8] for the exotic order and critical behavior. [4pt] [1] M. Maltseva, M. Dzero, and P. Coleman, Phys. Rev. Lett. 103, 206402 (2009).[0pt] [2] J. Figgins and D. Morr, Phys. Rev. Lett. 104, 187202 (2010).[0pt] [3] A. R. Schmidt et al, Nature 465, 570-576 (2010).[0pt] [4] P. Aynajian et al., Proc. Natl. Acad. Sci. U.S.A. 107, 10383 (2010).[0pt] [5] S. Ernst et al, Nature (2011).[0pt] [6] S. Ernst et al, Physica Status Solidi 247, 624 (2010).[0pt] [7] Y. Dubi and A.V. Balatsky, Phys. Rev. Lett. 106, 196407 (2011).[0pt] [8] P. Chandra, P. Coleman and R. Flint, to be published (2012).
Antiferroquadrupolar Ordering in Quadrupolar Kondo Lattice of Non-Kramers System PrTa2Al20
Higashinaka, Ryuji; Nakama, Akihiro; Miyazaki, Ryoichi; Yamaura, Jun-ichi; Sato, Hideyuki; Aoki, Yuji
2017-10-01
Single crystals of PrTa2Al20 have been investigated by means of single-crystal structural analysis and measurements of magnetization, specific heat, and electrical resistivity. The crystalline-electric-field level scheme of the Pr ions has a nonmagnetic Γ3 doublet ground state and a Γ5 magnetic excited state with an energy separation of 53 K. The 4f-electron contribution to the electrical resistivity shows -log T magnetic Kondo scattering above 50 K and a downward curvature characteristic of a quadrupolar Kondo lattice formation below 20 K. A phase transition appears at 0.65 K in zero field and shifts to higher temperatures in applied fields, indicating that this transition is antiferroquadrupolar (AFQ) in nature. The largely enhanced Sommerfeld coefficient ˜1.5 J/(mol K2) in the AFQ state may indicate the formation of heavy quasiparticles. The hierarchically arranged sequence of the magnetic Kondo regime, quadrupolar Kondo lattice regime, and AFQ ordered state in the wide temperature range 0.2-300 K demonstrates that PrTa2Al20 is a good playground to investigate quadrupole physics with strong electron correlations.
Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics
Steglich, Frank; Wirth, Steffen
2016-08-01
This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a ‘conventional’, itinerant QCP can be well understood within Landau’s paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an ‘unconventional’, local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.
Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics.
Steglich, Frank; Wirth, Steffen
2016-08-01
This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a 'conventional', itinerant QCP can be well understood within Landau's paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an 'unconventional', local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.
Isaev, L.; Schachenmayer, J.; Rey, A. M.
2016-09-01
We show that an interplay between quantum effects, strong on-site ferromagnetic exchange interaction, and antiferromagnetic correlations in Kondo lattices can give rise to an exotic spin-orbit coupled metallic state in regimes where classical treatments predict a trivial insulating behavior. This phenomenon can be simulated with ultracold alkaline-earth fermionic atoms subject to a laser-induced magnetic field by observing dynamics of spin-charge excitations in quench experiments.
Isaev, L; Schachenmayer, J; Rey, A M
2016-09-23
We show that an interplay between quantum effects, strong on-site ferromagnetic exchange interaction, and antiferromagnetic correlations in Kondo lattices can give rise to an exotic spin-orbit coupled metallic state in regimes where classical treatments predict a trivial insulating behavior. This phenomenon can be simulated with ultracold alkaline-earth fermionic atoms subject to a laser-induced magnetic field by observing dynamics of spin-charge excitations in quench experiments.
Importance of conduction electron correlation in a Kondo lattice, Ce{sub 2}CoSi{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Patil, Swapnil; Pandey, Sudhir K; Medicherla, V R R; Singh, R S; Bindu, R; Sampathkumaran, E V; Maiti, Kalobaran, E-mail: kbmaiti@tifr.res.i [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai-400 005 (India)
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, Ce{sub 2}CoSi{sub 3}, 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.
Nonequilibrium spatiotemporal formation of the Kondo screening cloud on a lattice
Nuss, Martin; Ganahl, Martin; Arrigoni, Enrico; von der Linden, Wolfgang; Evertz, Hans Gerd
2015-02-01
We study the nonequilibrium formation of a spin screening cloud that accompanies the quenching of a local magnetic moment immersed in a Fermi sea at zero temperature. Based on high-precision density matrix renormalization-group results for the interacting single-impurity Anderson model, we discuss the real-time evolution after a quantum quench in the impurity-reservoir hybridization using time-evolving block decimation. We report emergent length and time scales in the spatiotemporal structure of nonlocal correlation functions in the spin and the charge density channel. At equilibrium, our data for the correlation functions and the extracted length scales show good agreement with existing results, as do local time-dependent observables at the impurity. In the time-dependent data, we identify a major signal which defines a "light cone" moving at the Fermi velocity and a ferromagnetic component in its wake. Inside the light cone we find that the structure of the nonequilibrium correlation functions emerges on two time scales. Initially, the qualitative structure of the correlation functions develops rapidly at the lattice Fermi velocity. Subsequently the spin correlations converge to the equilibrium results on a much larger time scale. This process sets a dynamic energy scale, which we identify to be proportional to the Kondo temperature. Outside the light cone we observe two different power-law decays of the correlation functions in space, with time- and interaction-strength-independent exponents.
Fano resonance and hybridization gap in the Kondo lattice URu2Si2^*
Park, Wan Kyu; Tobash, P. H.; Ronning, F.; Bauer, E. D.; Sarrao, J. L.; Thompson, J. D.; Greene, L. H.
2012-02-01
The nature of the `hidden' order transition in URu2Si2 remains puzzling despite intensive research over the past two and half decades. A key question under debate is whether a hybridization gap between the renormalized bands can be identified as the long-sought hidden order parameter. We report on the measurement of a hybridization gap in URu2Si2 employing a spectroscopic technique based on quasiparticle scattering across a ballistic metallic junction [1]. The differential conductance data exhibit an asymmetric double-peak structure, a signature for a Fano resonance in a Kondo lattice [2]. The extracted hybridization gap opens well above the hidden order transition temperature, indicating that it is not the order parameter for the hidden order phase. Our results place constraints on the origin of the hidden order transition in URu2Si2.[4pt] [1] W. K. Park et al., arXiv:1110.5541.[0pt] [2] M. Maltseva, M. Dzero, P. Coleman, PRL 103, 206402 (2009).
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.)
Schilling, James S.; Song, Jing; Soni, Vikas; Lim, Jinhyuk
Most elemental lanthanides order magnetically at temperatures To well below ambient, the highest being 292 K for Gd. Sufficiently high pressure is expected to destabilize the well localized magnetic 4 f state of the heavy lanthanides, leading to increasing influence of Kondo physics on the RKKY interaction. For pressures above 80 GPa, To for Dy and Tb begins to increase dramatically, extrapolating for Dy to a record-high value near 400 K at 160 GPa. This anomalous increase may be an heretofore unrecognized feature of the Kondo lattice state; if so, one would expect To to pass through a maximum and fall rapidly at even higher pressures. A parallel is suggested to the ferromagnet CeRh3B2 where To = 115 K at ambient pressure, a temperature more than 100-times higher than anticipated from simple de Gennes scaling. Here we discuss recent experiments on Nd where anomalous behavior in To (P) is found to occur at lower pressures, perhaps reflecting the fact that Nd's 4 f wave function is less localized. Work at Washington University is supported by NSF Grant DMR-1104742 and CDAC through NNSA/DOE Grant DE-FC52-08NA28554.
Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Zhang, Wen; Lai, Xinchun; Donglai Feng Team; Huiqiu Yuan Team
One basic concept in heavy fermions systems is the entanglement of localized spin state and itinerant electron state. It can be tuned by two competitive intrinsic mechanisms, Kondo effect and Ruderman-Kittel-Kasuya-Yosida interaction, with external disturbances. The key issue regarding heavy fermions properties is how the two mechanisms work in the same phase region. To investigate the relation of the two mechanisms, the cubic antiferromagnetic heavy fermions compound CeIn3 was investigated by soft x-ray angle resolved photoemission spectroscopy. The hybridization between f electrons and conduction bands in the paramagnetic state was observed directly, providing compelling evidence for Kondo screening scenario and coexistence of two mechanisms. The hybridization strength shows slight and regular anisotropy in K space, implying that the two mechanisms are competitive and anisotropic. This work illuminates the concomitant and competitive relation between the two mechanisms and supplies some evidences for the anisotropic superconductivity of CeIn3
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)
Magnavita, E.T. [CCNH, Universidade Federal do ABC (UFABC), Santo André, SP, 09210-580 (Brazil); Rettori, C. [CCNH, Universidade Federal do ABC (UFABC), Santo André, SP, 09210-580 (Brazil); Instituto de Física “Gleb Wataghin”, UNICAMP, Campinas, SP, 13083-970 (Brazil); Osorio-Guillén, J.M. [Instituto de Física, Universidad de Antioquia UdeA, Calle 70 No 52-21, Medellín (Colombia); Ferreira, F.F.; Mendonça-Ferreira, L.; Avila, M.A.; Ribeiro, R.A. [CCNH, Universidade Federal do ABC (UFABC), Santo André, SP, 09210-580 (Brazil)
2016-06-05
A thorough transport and thermodynamic investigation of flux-grown single crystals of the ternary Zintl phase Yb{sub 11} AlSb{sub 9}, combined with first-principles density functional theory calculations, shows that this compound is a metal above T ≈ 100 K and a semiconductor with small hybridization gap at low-T. The general behavior resembles those of Kondo lattice semiconductors, although some of the measured properties are strongly sample dependent, as often seen in hybridized f-electron materials. We thus suggest that Yb{sub 11} AlSb{sub 9} can be considered as a new Yb-based Kondo lattice semiconductor joining the family of strongly correlated electron systems. - Highlights: • First characterization at low temperatures of Yb{sub 11}AlSb{sub 9}. • Yb{sub 11}AlSb{sub 9} has a small, field dependent hybridization gap at low-T. • Yb{sub 11}AlSb{sub 9} can be considered as a new Kondo lattice semiconductor.
Aoki, Dai; Paulsen, Carley; Kotegawa, Hisashi; Hardy, Frederic; Meingast, Christoph; Haen, Pierre; Boukahil, Mounir; Knafo, William; Ressouche, Eric; Raymond, Stephane; Flouquet, Jacques
2012-01-01
Doping Kondo lattice system CeRu2Si2 with Rh-8% (Ce(Ru0.92Rh0.08)2Si2) leads to drastic consequences due to the mismatch of the lattice parameters between CeRu2Si2 and CeRh2Si2. A large variety of experiments clarifies the unusual properties of the ground state induced by the magnetic field from longitudinal antiferromagnetic (AF) mode at H = 0 to polarized paramagnetic phase in very high magnetic field. The separation between AF phase, paramagnetic phase and polarized paramagnetic phase vary...
Three-dimensional bulk electronic structure of the Kondo lattice CeIn3 revealed by photoemission
Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Liu, Qin; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Liu, Yu; Song, Haifeng; Zhang, Zhengjun; Lai, Xinchun
2016-09-01
We show the three-dimensional electronic structure of the Kondo lattice CeIn3 using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic state. For the first time, we have directly observed the three-dimensional topology of the Fermi surface of CeIn3 by photoemission. The Fermi surface has a complicated hole pocket centred at the Γ-Z line and an elliptical electron pocket centred at the R point of the Brillouin zone. Polarization and photon-energy dependent photoemission results both indicate the nearly localized nature of the 4f electrons in CeIn3, consistent with the theoretical prediction by means of the combination of density functional theory and single-site dynamical mean-field theory. Those results illustrate that the f electrons of CeIn3, which is the parent material of CeMIn5 compounds, are closer to the localized description than the layered CeMIn5 compounds.
Aoki, Dai; Paulsen, Carley; Kotegawa, Hisashi; Hardy, Frédéric; Meingast, Christoph; Haen, Pierre; Boukahil, Mounir; Knafo, William; Ressouche, Eric; Raymond, Stephane; Flouquet, Jacques
2012-03-01
Doping Kondo lattice system CeRu2Si2 with Rh-8% (Ce(Ru0.92Rh0.08)2Si2) leads to drastic consequences due to the mismatch of the lattice parameters between CeRu2Si2 and CeRh2Si2. A large variety of experiments clarifies the unusual properties of the ground state induced by the magnetic field from longitudinal antiferromagnetic (AF) mode at H=0 to polarized paramagnetic phase in very high magnetic field. The separation between AF phase, paramagnetic phase and polarized paramagnetic phase varying with temperature, magnetic field and pressure is discussed on the basis of the experiments down to very low temperature. Similarities and differences between Rh and La substituted alloys are discussed with emphasis on the competition between transverse and longitudinal AF modes, and ferromagnetic fluctuations.
The Kondo lattice state in the presence of Van Hove singularities: Next-to-leading order scaling
Irkhin, V. Yu.
2017-07-01
Renormalization group analysis of the Kondo model with a logarithmic Van Hove singularity in the electron density of states has been carried out in the next-to-leading scaling approximation in different magnetic phases. The effective coupling constant remains small, while the renormalized magnetic moment and the frequency of spin fluctuations decrease by several orders of magnitude. In this way, broad regions of non-Fermi-liquid behavior are found from scaling trajectories in a large interval of the bare coupling constant. Applications to the physics of itinerant magnetism are considered.
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}
Competing Kondo Effects in Non-Kramers Doublet Systems
Kusunose, Hiroaki
2016-01-01
In non-Kramers Kondo systems with a quadrupolar degrees of freedom, an ordinary magnetic Kondo effect can compete with the quadrupolar Kondo effect. We discuss such competition keeping Pr$T_{2}$Zn$_{20}$ ($T$=Ir, Rh) and Pr$T_{2}$Al$_{20}$ ($T$=V, Ti) in mind, where the $\\Gamma_{3}$ non-Kramers crystalline-electric-field (CEF) doublet ground state is realized in Pr$^{3+}$ ion with $(4f)^{2}$ configuration under cubic symmetry. The quadrupolar Kondo effect can be described by the two-channel K...
Magneto-heat capacity study on Kondo lattice system Ce(Ni$_{1−x}$Cu$_x$)$_2$Al$_3$
Indian Academy of Sciences (India)
SANKARARAO YADAM; DURGESH SINGH; D VENKATESHWARLU; MOHAN KUMAR GANGRADE; S SHANMUKHA RAO SAMATHAM; V GANESAN
2016-04-01
Heat capacity studies on the Kondo lattice system Ce(Ni$_{1−x}$Cu$_x$)$_2$Al$_3$, in the presence of magnetic fields, were reported for $x = 0.0−0.4$. The physical properties of the intermediate compositions like $x = 0.3$ and 0.4 were known for their enhanced thermoelectric power and hence have been analysed with an extra interest. It was also shown from the X-ray diffraction that these systems with $x = 0.3$ and 0.4 were in single phase in terms of sample purity and it stabilized the phases easily with the increase in the Cu doping in the system. The low temperature risein $C_p/T$ below 10 K under the influence of high magnetic fields was analysed using a multi-level Schottky effect. A gradual decrease of the total angular momentum (J) with the increase of applied magnetic fields indicated ascenario of screening of Ce$^{3+}$ magnetic moment while simultaneously the system settled for the Fermi liquid state. The screening thus seen was in line with the expectations of electrical conductivity measurements on these samples.
Some transport properties of the two-channel Kondo impurity
Energy Technology Data Exchange (ETDEWEB)
Schlottmann, P. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Zvyagin, A.A. [B. I. Verkin Institute for Low Temperature Physics and Engineering of the Ukrainian Akademy of Sciences, 47 Lenin Ave., 310164, Kharkov (Ukraine)
1997-04-01
We consider conduction electrons moving along a ring in two different orbital channels interacting with a spin-1/2 impurity via isotropic spin exchange. The exchange is the same for both channels, but a crystalline field breaks the orbital symmetry. The tower structure of the finite size corrections to the ground state energy is derived from the Bethe ansatz equations and used to discuss the Aharonov{endash}Bohm{endash}Casher interference pattern in the persistent current and the magnetoresistivity. {copyright} {ital 1997 American Institute of Physics.}
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.
Competing Kondo Effects in Non-Kramers Doublet Systems
Kusunose, Hiroaki
2016-06-01
In non-Kramers Kondo systems with quadrupolar degrees of freedom, an ordinary magnetic Kondo effect can compete with the quadrupolar Kondo effect. We discuss such competition keeping PrT2Zn20 (T = Ir, Rh) and PrT2Al20 (T = V, Ti) in mind, where the Γ3 non-Kramers crystalline-electric-field (CEF) doublet ground state is realized in a Pr3+ ion with a (4f)2 configuration under cubic symmetry. The quadrupolar Kondo effect can be described by the two-channel Kondo model, which leads to the local non-Fermi-liquid (NFL) ground state, while the magnetic Kondo effect favors the ordinary local Fermi-liquid (FL) ground state. On the basis of the minimal extended two-channel Kondo model including the magnetic Kondo coupling as well, we investigate the competition and resulting thermodynamics, and orbital/magnetic and single-particle excitation spectra by Wilson's numerical renormalization group (NRG) method. There is a first-order transition between the NFL and FL ground states. In addition to these two states, the alternative FL state accompanied by a free magnetic spin appears in the intermediate temperature range, which eventually reaches the true NFL ground state, as a consequence of the stronger competition between the magnetic and quadrupolar Kondo effects. In this peculiar state, the magnetic susceptibility shows a Curie-like behavior, while the orbital fluctuation exhibits the FL behavior. Moreover, the single-particle spectra yield a more singular behavior. Implications to the Pr 1-2-20 systems are briefly discussed.
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.
Kondo Screening and Fermi Surface in the Antiferromagnetic Metal Phase
Yamamoto, Seiji; Si, Qimiao
2006-03-01
We address the Kondo effect deep inside the antiferromagnetic metal phase of a Kondo lattice Hamiltonian with SU(2) invariance. The local- moment component is described in terms of a non-linear sigma model. The Fermi surface of the conduction electron component is taken to be sufficiently small, so that it is not spanned by the antiferromagnetic wavevector. The effective low energy form of the Kondo coupling simplifies drastically, corresponding to the uniform component of the magnetization that forward-scatters the conduction electrons on their own Fermi surface. We use a combined bosonic and fermionic (Shankar) renormalization group procedure to analyze this effective theory and study the Kondo screening and Fermi surface in the antiferromagnetic phase. The implications for the global magnetic phase diagram, as well as quantum critical points, of heavy fermion metals are discussed.
Corrected Kondo temperature beyond the conventional Kondo scaling limit
Li, ZhenHua; Wei, JianHua; Zheng, Xiao; Yan, YiJing; Luo, Hong-Gang
2017-05-01
In the Kondo systems such as the magnetic impurity screened by the conduction electrons in a metal host, as well as the quantum dots connected by the leads, the low energy behaviors have universal dependence on the T/T\\text{K}0 or eV/{{k}\\text{B}}T\\text{K}0 , where T\\text{K}0 is the conventional Kondo temperature. However, it was shown that this scaling behavior is only valid at low-energy; this is called the Kondo scaling limit. Here we explore the extention of the scaling parameter range by introducing the corrected Kondo temperature T K, which may depend on the temperature and bias, as well as the other external parameters. We define the corrected Kondo temperature by scaling the local density of states near the Fermi level, obtained by accurate hierarchy of equations of motion approach at finite temperature and finite bias, and thus obtain a phenomenological expression of the corrected Kondo temperature. By using the corrected Kondo temperature as a characteristic energy scale, the conductance of the quantum dot can be well scaled in a wide parameter range, even two orders beyond the conventional scaling parameter range. Our work indicates that the Kondo scaling, although dominated by the conventional Kondo temperature in the low-energy of the Kondo system, could be extended to a higher energy regime, which is useful for analyzing the physics of the Kondo transport in non-equilibrium or high temperature cases.
Corrected Kondo temperature beyond the conventional Kondo scaling limit.
Li, ZhenHua; Wei, JianHua; Zheng, Xiao; Yan, YiJing; Luo, Hong-Gang
2017-02-20
In the Kondo systems such as the magnetic impurity screened by the conduction electrons in a metal host, as well as the quantum dots connected by the leads, the low energy behaviors have universal dependence on the [Formula: see text] or [Formula: see text], where [Formula: see text] is the conventional Kondo temperature. However, it was shown that this scaling behavior is only valid at low-energy; this is called the Kondo scaling limit. Here we explore the extention of the scaling parameter range by introducing the corrected Kondo temperature T K, which may depend on the temperature and bias, as well as the other external parameters. We define the corrected Kondo temperature by scaling the local density of states near the Fermi level, obtained by accurate hierarchy of equations of motion approach at finite temperature and finite bias, and thus obtain a phenomenological expression of the corrected Kondo temperature. By using the corrected Kondo temperature as a characteristic energy scale, the conductance of the quantum dot can be well scaled in a wide parameter range, even two orders beyond the conventional scaling parameter range. Our work indicates that the Kondo scaling, although dominated by the conventional Kondo temperature in the low-energy of the Kondo system, could be extended to a higher energy regime, which is useful for analyzing the physics of the Kondo transport in non-equilibrium or high temperature cases.
The role of short-range magnetic correlations in the gap opening of topological Kondo insulators
Ramos, E.; Franco, R.; Silva-Valencia, J.; Foglio, M. E.; Figueira, M. S.
2017-08-01
In this article we investigate the effects of short-range anti-ferromagnetic correlations on the gap opening of topological Kondo insulators. We add a Heisenberg term to the periodic Anderson model at the limit of strong correlations in order to allow a small degree of hopping of the localized electrons between neighboring sites of the lattice. This new model is adequate for studying topological Kondo insulators, whose paradigmatic material is the compound SmB6 . The main finding of the article is that the short-range antiferromagnetic correlations, present in some Kondo insulators, contribute decisively to the opening of the Kondo gap in their density of states. These correlations are produced by the interaction between moments on the neighboring sites of the lattice. For simplicity, we solve the problem on a two dimensional square lattice. The starting point of the model is the 4f-Ce ions orbitals, with J=5/2 multiplet in the presence of spin-orbit coupling. We present results for the Kondo and for the antiferromagnetic correlation functions. We calculate the phase diagram of the model, and as we vary the Ef level position from the empty regime to the Kondo regime, the system develops metallic and topological Kondo insulator phases. The band structure calculated shows that the model describes a strong topological insulator.
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.
Lateral manipulation and interplay of local Kondo resonances in a two-impurity Kondo system
Energy Technology Data Exchange (ETDEWEB)
Ren, Jindong; Wu, Xu; Guo, Haiming, E-mail: hmguo@iphy.ac.cn; Pan, Jinbo; Du, Shixuan; Gao, Hong-Jun [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Luo, Hong-Gang [Center for Interdisciplinary Studies and Key Laboratory for Magnetism and Magnetic Materials of the MoE, Lanzhou University, Lanzhou 730000 (China); Beijing Computational Science Research Center, Beijing 100084 (China)
2015-08-17
The atomic-scale spatial relationship of a two-impurity Kondo system has been determined at varying lateral distance by scanning tunneling microscopy (STM) and spectroscopy. The localized spins of two cobalt magnetic adatoms that are placed on different electrodes of an STM form two individual Kondo singlet states, each showing quite different Kondo coupling, i.e., the tip-Kondo with low Kondo temperature and the sample-Kondo with high Kondo temperature. The differential conductance dI/dV spectra show the continuous changes of the resonance peak feature when approaching the Kondo tip laterally to the local sample-Kondo impurity on the surface. The result indicates a notable interplay between these two Kondo systems. We propose a convolution model based on the q factor of the sample-Kondo (q{sub s}) and tip-Kondo (q{sub t}) to interpret the change of various tunneling channels and the evolution of the experimental spectra.
Exact results for the Kondo screening cloud of two helical liquids.
Posske, Thore; Liu, Chao-Xing; Budich, Jan Carl; Trauzettel, Björn
2013-01-04
We analyze the screening of a magnetic quantum dot with spin 1/2 coupled to two helical liquids. Interestingly, we find two qualitatively different sets of Toulouse points, i.e., nontrivial parameters for which we can solve the two channel Kondo model exactly. This enables us to calculate the temperature and voltage dependent Kondo screening cloud, which develops oscillations for an applied spin voltage μ(s). Such a spin voltage can be conveniently applied by a charge bias in a four-terminal helical liquid setup.
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2-δAs2.
Luo, Yongkang; Ronning, F; Wakeham, N; Lu, Xin; Park, Tuson; Xu, Z-A; Thompson, J D
2015-11-03
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2-δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ~0.032 E-/formular unit in CeNi2-δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2−δAs2
Luo, Yongkang; Ronning, F.; Wakeham, N.; Lu, Xin; Park, Tuson; Xu, Z.-A.; Thompson, J. D.
2015-01-01
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2−δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ∼0.032 e−/formular unit in CeNi2−δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening. PMID:26483465
Consequences of Kondo exchange on quantum spins
Delgado Acosta, Fernando; Hirjibehedin, Cyrus F.; Fernández Rossier, Joaquín
2014-01-01
When individual quantum spins are placed in close proximity to conducting substrates, the localized spin is coupled to the nearby itinerant conduction electrons via Kondo exchange. In the strong coupling limit this can result in the Kondo effect — the formation of a correlated, many body singlet state — and a resulting renormalization of the density of states near the Fermi energy. However, even when Kondo screening does not occur, Kondo exchange can give rise to a wide variety of other pheno...
Magnetically induced QCD Kondo effect
Ozaki, Sho; Itakura, Kazunori; Kuramoto, Yoshio
2016-10-01
The "QCD Kondo effect" stems from the color exchange interaction in QCD with non-Abelian property, and can be realized in a high-density quark matter containing heavy-quark impurities. We propose a novel type of the QCD Kondo effect induced by a strong magnetic field. In addition to the fact that the magnetic field does not affect the color degrees of freedom, two properties caused by the Landau quantization in a strong magnetic field are essential for the "magnetically induced QCD Kondo effect"; (1) dimensional reduction to 1 +1 -dimensions, and (2) finiteness of the density of states for lowest energy quarks. We demonstrate that, in a strong magnetic field B , the scattering amplitude of a massless quark off a heavy quark impurity indeed shows a characteristic behavior of the Kondo effect. The resulting Kondo scale is estimated as ΛK≃√{eqB }αs1 /3exp {-4 π /Ncαslog (4 π /αs)} where αs and Nc are the fine structure constant of strong interaction and the number of colors in QCD, and eq is the electric charge of light quarks.
A Maximally Supersymmetric Kondo Model
Energy Technology Data Exchange (ETDEWEB)
Harrison, Sarah; Kachru, Shamit; Torroba, Gonzalo; /Stanford U., Phys. Dept. /SLAC
2012-02-17
We study the maximally supersymmetric Kondo model obtained by adding a fermionic impurity to N = 4 supersymmetric Yang-Mills theory. While the original Kondo problem describes a defect interacting with a free Fermi liquid of itinerant electrons, here the ambient theory is an interacting CFT, and this introduces qualitatively new features into the system. The model arises in string theory by considering the intersection of a stack of M D5-branes with a stack of N D3-branes, at a point in the D3 worldvolume. We analyze the theory holographically, and propose a dictionary between the Kondo problem and antisymmetric Wilson loops in N = 4 SYM. We perform an explicit calculation of the D5 fluctuations in the D3 geometry and determine the spectrum of defect operators. This establishes the stability of the Kondo fixed point together with its basic thermodynamic properties. Known supergravity solutions for Wilson loops allow us to go beyond the probe approximation: the D5s disappear and are replaced by three-form flux piercing a new topologically non-trivial S3 in the corrected geometry. This describes the Kondo model in terms of a geometric transition. A dual matrix model reflects the basic properties of the corrected gravity solution in its eigenvalue distribution.
Holographic Kondo and Fano Resonances
Erdmenger, Johanna; O'Bannon, Andy; Papadimitriou, Ioannis; Probst, Jonas; Wu, Jackson M S
2016-01-01
We use holography to study a $(1+1)$-dimensional Conformal Field Theory (CFT) coupled to an impurity. The CFT is an $SU(N)$ gauge theory at large $N$, with strong gauge interactions. The impurity is an $SU(N)$ spin. We trigger an impurity Renormalization Group (RG) flow via a Kondo coupling. The Kondo effect occurs only below the critical temperature of a large-$N$ mean-field transition. We show that at all temperatures $T$, spectral functions of certain bosonic operators exhibit a Fano resonance, which in the low-$T$ phase is a large-$N$ manifestation of the Kondo resonance. Such Fano resonances are characteristic features of RG flows between $(0+1)$-dimensional fixed points, and are thus distinct from those observed for example in quantum dots.
The Spin Glass-Kondo Competition in Disordered Cerium Systems
Magalhaes, S. G.; Zimmer, F.; Coqblin, B.
2013-10-01
We discuss the competition between the Kondo effect, the spin glass state and a magnetic order observed in disordered Cerium systems. We present firstly the experimental situation of disordered alloys such as CeNi1 - xCux and then the different theoretical approaches based on the Kondo lattice model, with different descriptions of the intersite exchange interaction for the spin glass. After the gaussian approach of the Sherrington-Kirkpatrick model, we discuss the Mattis and the van Hemmen models. Then, we present simple cluster calculations in order to describe the percolative evolution of the clusters from the cluster spin glass to the inhomogeneous ferromagnetic order recently observed in CeNi1 - xCux disordered alloys and finally we discuss the effect of random and transverse magnetic field.
Thermoelectric power of Kondo insulators
佐宗, 哲郎
2002-01-01
Thermoelectric power (TEP) of the Kondo insulators is investigated theoretically within the framework of the dynamical mean field theory. It is found that the temperature dependence of the Seebeck coefficient changes from the ordinary behavior S(T) ∝ T−1 in semiconductors to S ∝ T at low temperatures due to the finite imaginary part of the electron self-energy in the Kondo insulators with strong correlation. Realistic models for YbB12 and FeSi based on the band calculations are also studied....
Spatially dependent Kondo effect in Quantum Corrals
Rossi, Enrico; Morr, Dirk K.
2007-03-01
We study the Kondo screening of a single magnetic impurity placed inside a quantum corral consisting of non-magnetic impurities on the surface of a metallic host system. We show that the spatial structure of the corral's eigenmodes leads to a spatially dependent Kondo effect whose signatures are experimentally measurable spatial variations of the Kondo temperature, TK, and of the critical Kondo coupling, Jcr. Moreover we find that the screening of the magnetic impurity is accompanied by the formation of multiple Kondo resonances with characteristic spatial patterns that provide further experimental signatures of the spatially dependent Kondo effect. Our results demonstrate that quantum corrals provide new possibilities to manipulate and explore the Kondo effect.
Two-channel X-ray reflectometer
Touryanski, A G; Pirshin, I V
2000-01-01
The two-channel X-ray reflectometer is proposed providing an increase in accuracy and sensitivity especially to nanoscale oxide layers. The reflectometer has two independent measuring channels controlled by a processor and the beam-splitting and spectral selection device based on a row of semitransparent plates of pyrolitic graphite. Results of reflection curve measurements in a relative mode are presented for an Ni film and GaAs monocrystal.
Phase diagram of the bosonic Kondo-Hubbard model
Energy Technology Data Exchange (ETDEWEB)
Foss-Feig, Michael; Rey, Ana Maria [JILA, National Institute of Standards and Technology, and University of Colorado, Boulder, Colorado 80309 (United States)
2011-11-15
We study a bosonic version of the Kondo lattice model with an onsite repulsion in the conduction band, implemented with alkali-metal atoms in two bands of an optical lattice. Using both weak- and strong-coupling perturbation theory, we find that at unit filling of the conduction bosons the superfluid-to-Mott-insulator transition should be accompanied by a magnetic transition from a ferromagnet (in the superfluid) to a paramagnet (in the Mott insulator). Furthermore, an analytic treatment of Gutzwiller mean-field theory reveals that quantum spin fluctuations induced by the Kondo exchange cause the otherwise continuous superfluid-to-Mott-insulator phase transition to be first order. We show that lattice separability imposes a serious constraint on proposals to exploit excited bands for quantum simulations, and discuss a way to overcome this constraint in the context of our model by using an experimentally realized nonseparable lattice. A method to probe the first-order nature of the transition based on collapses and revivals of the matter-wave field is also discussed.
TWO-CHANNEL DIELECTRIC WAKE FIELD ACCELERATOR
Energy Technology Data Exchange (ETDEWEB)
Jay L. Hirshfield
2012-05-30
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 {approx}30 GHz, and the structure is configured to exhibit a high transformer ratio ({approx}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.
Kondo route to spin inhomogeneities in the honeycomb Kitaev model
Energy Technology Data Exchange (ETDEWEB)
Das, S. D.; Dhochak, K.; Tripathi, V.
2016-07-01
Paramagnetic impurities in a quantum spin liquid give rise to Kondo effects with highly unusual properties. We have studied the effect of locally coupling a paramagnetic impurity with the spin-1/2 honeycomb Kitaev model in its gapless spin-liquid phase. The ( impurity) scaling equations are found to be insensitive to the sign of the coupling. The weak and strong coupling fixed points are stable, with the latter corresponding to a noninteracting vacancy and an interacting, spin-1 defect for the antiferromagnetic and ferromagnetic cases, respectively. The ground state in the strong coupling limit in both cases has a nontrivial topology associated with a finite Z(2) flux at the impurity site. For the antiferromagnetic case, this result has been obtained straightforwardly owing to the integrability of the Kitaev model with a vacancy. The strong-coupling limit of the ferromagnetic case is, however, nonintegrable, and we address this problem through exact-diagonalization calculations with finite Kitaev fragments. Our exact diagonalization calculations indicate that the weak-to-strong coupling transition and the topological phase transition occur rather close to each other and are possibly coincident. We also find an intriguing similarity between the magnetic response of the defect and the impurity susceptibility in the two-channel Kondo problem.
Competition between Quadrupole and Magnetic Kondo Effects in Non-Kramers Doublet Systems
Kusunose, Hiroaki; Onimaru, Takahiro
2015-03-01
We discuss possible competition between magnetic and quadrupole Kondo effects in non-Kramers doublet systems in cubic symmetry. The quadrupole Kondo effect leads to non-Fermi-liquid (NFL) ground state, while the magnetic one favors ordinary Fermi-liquid (FL) ground state. In terms of the j-j coupling scheme, we argue that the orbital fluctuation must develop in the vicinity of the NFL-FL boundary. A change of temperature dependence of the f-electron entropy in both the FL and NFL regimes is demonstrated by the Wilson's numerical renormalization-group (NRG) method on the basis of the extended two-channel Kondo exchange model. We present implications to PrT2X20 (T=Ti, V, Ir; X=Al, Zn) systems which exhibit both quadrupole ordering and peculiar superconductivity. We discuss how the magnetic field lifts the non-Kramers degeneracy. Our model also represents the alternative FL state accompanied by a free magnetic spin, as a consequence of stronger competition between the magnetic and the quadrupole Kondo effects.
Mitchell, Andrew K.; Becker, Michael; Bulla, Ralf
2011-09-01
The existence of a length scale ξK˜1/TK (with TK the Kondo temperature) has long been predicted in quantum impurity systems. At low temperatures T≪TK, the standard interpretation is that a spin-(1)/(2) impurity is screened by a surrounding “Kondo cloud” of spatial extent ξK. We argue that renormalization group (RG) flow between any two fixed points (FPs) results in a characteristic length scale, observed in real space as a crossover between physical behavior typical of each FP. In the simplest example of the Anderson impurity model, three FPs arise, and we show that “free orbital,” “local moment,” and “strong coupling” regions of space can be identified at zero temperature. These regions are separated by two crossover length scales ξLM and ξK, with the latter diverging as the Kondo effect is destroyed on increasing temperature through TK. One implication is that moment formation occurs inside the “Kondo cloud”, while the screening process itself occurs on flowing to the strong coupling FP at distances ˜ξK. Generic aspects of the real-space physics are exemplified by the two-channel Kondo model, where ξK now separates local moment and overscreening clouds.
Kiss, Annamaria; Kuramoto, Yoshio; Hoshino, Shintaro
2011-01-01
Accurate numerical results are derived for transport properties of Kondo impurity systems with potential scattering and orbital degeneracy. Using the continuous-time quantum Monte Carlo (CT-QMC) method, static and dynamic physical quantities are derived in a wide temperature range across the Kondo temperature T_K. With strong potential scattering, the resistivity tends to decrease with decreasing temperature, in contrast to the ordinary Kondo effect. Correspondingly, the quasi-particle densit...
Chang, Po-Yao; Erten, Onur; Coleman, Piers
2017-08-01
Heavy fermion materials have recently attracted attention for their potential to combine topological protection with strongly correlated electron physics. To date, the ideas of topological protection have been restricted to the heavy fermion or `Kondo' insulators with the simplest point-group symmetries. Here we argue that the presence of nonsymmorphic crystal symmetries in many heavy fermion materials opens up a new family of topologically protected heavy electron systems. Re-examination of archival resistivity measurements in the nonsymmorphic heavy fermion insulators Ce3Bi4Pt3 and CeNiSn reveals the presence of a low-temperature conductivity plateau, making them candidate members of the new class of material. We illustrate our ideas with a specific model for CeNiSn, showing how glide symmetries generate surface states with a novel Möbius braiding that can be detected by ARPES or non-local conductivity measurements. One of the interesting effects of strong correlation is the development of partially localization or `Kondo breakdown' on the surfaces, which transforms Möbius surface states into quasi-one-dimensional conductors, with the potential for novel electronic phase transitions.
Single crystal study on a novel Kondo compound Ce{sub 6}Pt{sub 11}In{sub 14}
Energy Technology Data Exchange (ETDEWEB)
Pikul, A.P. E-mail: a.pikul@int.pan.wroc.pl; Bukowski, Z.; Stepien-Damm, J.; Kaczorowski, D
2004-05-01
Ce{sub 6}Pt{sub 11}In{sub 14} crystallizes with a monoclinic unit cell (space group C2/m; lattice parameters: a=22.729(5) A, b=4.3960(10) A, c=14.780(3) A, {beta}=118.35(3) deg.; Z=2). It is paramagnetic down to 1.9 K, and strongly anisotropic in the entire temperature range studied. The electrical resistivity along the b-axis shows Kondo features with a maximum located at 7 K. The transverse magnetoresistivity isotherms, measured in the incoherent region, follow a single-ion Kondo scaling with the characteristic temperature T*=4 K.
Competition between Kondo effect and RKKY physics in graphene magnetism
Allerdt, A.; Feiguin, A. E.; Das Sarma, S.
2017-03-01
The cooperative behavior of quantum impurities on two-dimensional (2D) materials, such as graphene and bilayer graphene, is characterized by a nontrivial competition between screening (Kondo effect) and Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetism. In addition, due to the small density of states at the Fermi level, impurities may not couple to the conduction electrons at all, behaving as free moments. Employing a recently developed exact numerical method to study multi-impurity lattice systems, we obtain nonperturbative results that dramatically depart from expectations based on the conventional RKKY theory. At half filling and for weak coupling, impurities remain in the local moment regime when they are on opposite sublattices, up to a critical value of the interactions when they start coupling antiferromagnetically with correlations that decay very slowly with interimpurity distance. At finite doping, away from half filling, ferromagnetism is completely absent and the physics is dominated by a competition between antiferromagnetism and Kondo effect. In bilayer graphene, impurities on opposite layers behave as free moments, unless the interaction is of the order of the hopping or larger.
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 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.
Vojta, Matthias; Mitchell, Andrew K; Zschocke, Fabian
2016-07-15
Kitaev's honeycomb-lattice compass model describes a spin liquid with emergent fractionalized excitations. Here, we study the physics of isolated magnetic impurities coupled to the Kitaev spin-liquid host. We reformulate this Kondo-type problem in terms of a many-state quantum impurity coupled to a multichannel bath of Majorana fermions and present the numerically exact solution using Wilson's numerical renormalization group technique. Quantum phase transitions occur as a function of Kondo coupling and locally applied field. At zero field, the impurity moment is partially screened only when it binds an emergent gauge flux, while otherwise it becomes free at low temperatures. We show how Majorana degrees of freedom determine the fixed-point properties, make contact with Kondo screening in pseudogap Fermi systems, and discuss effects away from the dilute limit.
Continuous Time Quantum Monte Carlo simulation of Kondo shuttling
Zhang, Peng; Assaad, Fakher; Jarrell, Mark
2010-03-01
The Kondo shuttling problem is investigated by using the Continuous Time Quantum Monte Carlo method in both the anti-adiabatic limit φTK and the intermediate regime φ˜TK, where φ is the phonon modulation frequency and TK is the Kondo temperature. We investigate the potential emergence of Kondo effect or Kondo breakdown as a function of the phonon modulation frequency and electron-phonon coupling. This research is supported by grant OISE-0952300.
Kondo effect in low-carrier systems
Energy Technology Data Exchange (ETDEWEB)
Hager, R.; Bulla, R. [Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Univ. Augsburg (Germany)
2007-07-01
Recent experiments on dilute U impurities in semiconducting CaB{sub 6} show typical Kondo phenomena with a Kondo temperature T{sub K}{approx}2 K (G.A. Wigger e.t al., Europhys. Lett. 68, 685 (2004)). This observation is rather unusual for magnetic moments due to 5f electrons because of the large hybridization between impurities and the conduction electrons. We perform numerical renormalization group calculations for an Anderson impurity model with a, low concentration of conduction electrons, believed to be the relevant model for (U,Ca)B{sub 6}. We present results for thermodynamic and dynamic quantities for various carrier concentrations and investigate the crossover from mixed-valent to Kondo behaviour upon decreasing the filling of the conduction band. (orig.)
Kondo effect in quantum dots and molecular devices
Institute of Scientific and Technical Information of China (English)
JIANG Lang; LI Hongxiang; HU Wenping; ZHU Daoben
2005-01-01
Kondo effect is a very important many-body phenomenon in condensed matter physics,which explains why the resistance increases as the temperature is lowered (usually <10 K) in dilute magnetic alloy, and why the conductance increases as temperature is decreased in quantum dots. This paper simply introduces equilibrium and non- equilibrium Kondo effects in quantum dots together with the Kondo effect in quantum dots with even number of electrons (when the singlet and triplet states are degenerate). Furthermore, Kondo effect in single atom/molecular transistors is introduced, which indicates a new way to study Kondo effect.
Kondo effect in molecules with strong correlations
Energy Technology Data Exchange (ETDEWEB)
Kuzmenko, Tetyana [Department of Physics, Ben-Gurion University, P.O. Box 653, Beer-Sheva 84105 (Israel)]. E-mail: tetyana@bgumail.bgu.ac.il; Kikoin, Konstantin [Department of Physics, Ben-Gurion University, P.O. Box 653, Beer-Sheva 84105 (Israel); Avishai, Yshai [Department of Physics, Ben-Gurion University, P.O. Box 653, Beer-Sheva 84105 (Israel)
2005-04-30
A theory of Kondo tunneling through molecules adsorbed on metallic substrate is constructed and the underlying physics is exposed. It is shown that in the case of weak chemisorption the sandwich-type molecules manifest a novel type of Kondo effect that has not been observed in magnetically doped bulk metals. The exchange Hamiltonian of these molecules unveils unusual dynamical SO(n) symmetries instead of conventional SU(2) symmetry. These symmetries can be experimentally realized and the specific value of n can be controlled by gate voltage.
Kondo tunneling through real and artificial molecules.
Kikoin, K; Avishai, Y
2001-03-05
When an asymmetric double dot is hybridized with itinerant electrons, its singlet ground state and lowly excited triplet state cross, leading to a competition between the Zhang-Rice mechanism of singlet-triplet splitting in a confined cluster and the Kondo effect (which accompanies the tunneling through quantum dot under a Coulomb blockade restriction). The rich physics of an underscreened S = 1 Kondo impurity in the presence of low-lying triplet-singlet excitations is exposed and estimates of the magnetic susceptibility and the electric conductance are presented, together with applications for molecule chemisorption on metallic substrates.
Transport across two interacting quantum dots: bulk Kondo, Kondo box and molecular regimes
Costa Ribeiro, Laercio; Hamad, Ignacio; Chiappe, Guillermo; Victoriano Anda, Enrique
2014-03-01
We analyze the transport properties of a double quantum dot device with both dots coupled to perfect conducting leads and to a finite chain of N non-interacting sites connecting both of them. The inter-dot chain strongly influences the transport across the system and the local density of states of the dots. We study the case of small number of sites, so that Kondo box effects are present. For odd N and small coupling between the inter-dot chain and the dots, a state with two coexisting Kondo regimes develops: the bulk Kondo due to the quantum dots connected to leads and the one produced by the screening of the quantum dots spins by the spin in the finite chain. As the coupling to the inter-dot chain increases, there is a crossover to a molecular Kondo effect, due to the screening of the molecule spin by the leads. For even N the two-Kondo temperatures regime does not develop and the physics is dominated by the usual competition between Kondo and antiferromagnetism. We finally study how the transport properties are affected as N is increased. We used exact multi-configurational Lanczos calculations and finite U slave-boson mean-field theory. The results obtained with both methods describe qualitatively and also quantitatively the same physics.
Transport properties of fully screened Kondo models
Hörig, Christoph B M; Mora, Christophe; Schuricht, Dirk
2014-01-01
We study the nonequilibrium transport properties of fully (exactly) screened Kondo quantum dots subject to a finite bias voltage or a finite temperature. First, we calculate the Fermi-liquid coefficients of the conductance for models with arbitrary spin, i.e., its leading behavior for small bias vol
The Kondo tip decorated by the Co atom
Feng, Wei; Liu, Qin; Lai, Xinchun; Zhao, Aidi
2016-11-01
The Kondo effect of single Co adatoms on Ru(0001) is detected with two different kinds of co-decorated tip (Kondo tip) by using low temperature scanning tunneling microscopy and scanning tunneling spectroscopy. We call the relatively separated two magnetic impurities in the tunneling region ‘two Kondo system’ to distinguish it from the ‘two-impurity Kondo system’. We find that the artificially constructed Kondo tips can be generally categorized into two types of Kondo resonances, which have distinct Fano line shapes with quantum interference factor |q| ≫ 1 and |q| ∼ 1, respectively. The tunneling spectra of six constructed two Kondo systems can be well fitted by summing the two Fano resonances of the two subsystems and a linear background. More interestingly, by extracting the amplitudes of the two Fano resonances in the spectra, we find that the electron transmission of such a two Kondo system in the tunneling region is dominated by the quantum interference of the Kondo tip, which is directly related to the geometric configuration of the adsorbed Kondo atom on the tip.
The possibility of nanostructure character in approaching Kondo effect
Energy Technology Data Exchange (ETDEWEB)
Kamali, N; Yazdani, A; Shahsavari, L [Tarbiat Modares University, Jalal al Ahmad, P. O. Box 14115-175, Tehran (Iran, Islamic Republic of)
2007-12-15
Based on instability of magnetic structure, a new class of heavy fermions is constructed with a stable local magnetic ion 'Gd'. The lattice constants, D.C magnetic susceptibility and the electrical resistivity measurements in the magnetic unstable intermetallic compounds show; (1) the Instability of crystal structure, as well as high transition temperature 'T{sub c}', strongly depends on the conduction electrons concentration. The reduced size effect and the reduction in correlation length, is expected to be the cause of this behaviour as it could be due to the nanostructure character as well as the competition of inter and intra-cluster also (2) the coexistence of Kondo lattice behaviour and magnetic ordering 'reentrant antiferromagnet' for the temperature range of 30 < T{sub k} < 90K with T{sub N} = T{sub max} = 30K and finally (3) the metal-insulator-like behaviour with complete quench of magnetic ordering occur antiferromagnetically named 'super paramagnet' at a certain conduction electron concentration.
Cai, Ang; Pixley, Jedediah; Si, Qimiao
Heavy fermion metals represent a canonical system to study superconductivity driven by quantum criticality. We are particularly motivated by the properties of CeRhIn5, which shows the characteristic features of a Kondo destruction quantum critical point (QCP) in its normal state, and has one of the highest Tc's among the heavy fermion superconductors. As a first step to study this problem within a cluster-EDMFT approach, we analyze a four-site Anderson impurity model with the antiferromagnetic spin component of the cluster coupled to a sub-Ohmic bosonic bath. We find a QCP that belongs to the same universality class as the single-site Bose-Fermi Anderson model. Together with previous work on a two-site model, our result suggests that the Kondo destruction QCP is robust as cluster size increases. More importantly, we are able to calculate the d-wave pairing susceptibility, which we find to be enhanced near the QCP. Using this model as the effective cluster model of the periodic Anderson model, we are also able to study the superconducting pairing near the Kondo-destruction QCP of the lattice model; preliminary results will be presented.
Dynamical symmetries in Kondo tunneling through complex quantum dots.
Kuzmenko, T; Kikoin, K; Avishai, Y
2002-10-07
Kondo tunneling reveals hidden SO(n) dynamical symmetries of evenly occupied quantum dots. As is exemplified for an experimentally realizable triple quantum dot in parallel geometry, the possible values n=3,4,5,7 can be easily tuned by gate voltages. Following construction of the corresponding o(n) algebras, scaling equations are derived and Kondo temperatures are calculated. The symmetry group for a magnetic field induced anisotropic Kondo tunneling is SU(2) or SO(4).
Kondo force in shuttling devices: dynamical probe for a Kondo cloud.
Kiselev, M N; Kikoin, K A; Gorelik, L Y; Shekhter, R I
2013-02-08
We consider the electromechanical properties of a single-electronic device consisting of a movable quantum dot attached to a vibrating cantilever, forming a tunnel contact with a nonmovable source electrode. We show that the resonance Kondo tunneling of electrons amplifies exponentially the strength of nanoelectromechanical (NEM) coupling in such a device and make the latter insensitive to mesoscopic fluctuations of electronic levels in a nanodot. It is also shown that the study of a Kondo-NEM phenomenon provides additional (as compared with standard conductance measurements in a nonmechanical device) information on retardation effects in the formation of a many-particle cloud accompanying the Kondo tunneling. A possibility for superhigh tunability of mechanical dissipation as well as supersensitive detection of mechanical displacement is demonstrated.
Kondo Effect at a Quantum Critical Point
Ramazashvili, Revaz; Coleman, Piers
1998-03-01
The Kondo effect in a metal on the verge of a zero-temperature magnetic instability provides a fascinating example of interference between local and long-range correlations. (A. I. Larkin and V. I. Mel'nikov, Sov. Phys. JETP 34, 656 (1972)) (P. Coleman and A. M. Tsvelik, cond-mat/9707003) (A. Sengupta, cond-mat/9707316) We discuss possible consequences of this interference, including the breakdown of the Fermi liquid state.
First passage time statistics for two-channel diffusion
Godec, Aljaz
2016-01-01
We present rigorous results for the mean first passage time and first passage time statistics for two-channel Markov additive diffusion in a 3-dimensional spherical domain. Inspired by biophysical examples we assume that the particle can only recognise the target in one of the modes, which is shown to effect a non-trivial first passage behaviour. We also address the scenario of intermittent immobilisation. In both cases we prove that despite the perfectly non-recurrent motion of two-channel Markov additive diffusion in 3 dimensions the first passage statistics at long times do not display Poisson-like behaviour if none of the phases has a vanishing diffusion coefficient. This stands in stark contrast to the standard (one-channel) Markov diffusion counterpart. We also discuss the relevance of our results in the context of cellular signalling.
Kondo behavior and conductance through 3d impurities in gold chains doped with oxygen
Barral, M. A.; Di Napoli, S.; Blesio, G.; Roura-Bas, P.; Camjayi, A.; Manuel, L. O.; Aligia, A. A.
2017-03-01
Combining ab initio calculations and effective models derived from them, we discuss the electronic structure of oxygen doped gold chains when one Au atom is replaced by any transition-metal atom of the 3d series. The effect of O doping is to bring extended Au 5dxz and 5dyz states to the Fermi level, which together with the Au states of zero angular momentum projection leads to three possible channels for the screening of the magnetism of the impurity. For most 3d impurities the expected physics is similar to that of the underscreened Kondo model, with singular Fermi liquid behavior. For Fe and Co under a tetragonal crystal field introduced by leads, the system might display a non-Fermi liquid behavior. Ni and Cu impurities are described by a S = 1 two channel Kondo model and an SU(4) impurity Anderson model in the intermediate valence regime, respectively. In both cases, the system is a Fermi liquid, but the conductance shows some observable differences with the ordinary SU(2) Anderson model.
Kondo effects in triangular triple quantum dots
Oguri, Akira; Numata, Takahide; Nisikawa, Yunori; Hewson, A. C.
2009-03-01
We study the conductance through a triangular triple quantum dot, which is connected to two noninteracting leads, using the numerical renormalization group (NRG). It is found that the system shows a variety of Kondo effects depending on the filling of the triangle. The SU(4) Kondo effect occurs at half-filling, and a sharp conductance dip due to a phase lapse appears in the gate-voltage dependence. Furthermore, when four electrons occupy the three sites on average, a local S=1 moment, which is caused by the Nagaoka mechanism, is induced along the triangle. The temperature dependence of the entropy and spin susceptibility of the triangle shows that this moment is screened by the conduction electrons via two separate stages at different temperatures. The two-terminal and four-terminal conductances show a clear difference at the gate voltages, where the SU(4) or the S=1 Kondo effects occur[1]. We will also discuss effects of deformations of the triangular configuration, caused by the inhomogeneity in the inter-dot couplings and in the gate voltages. [4pt] [1] T.Numata, Y.Nisikawa, A.Oguri, and A.C.Hewson: arXiv:0808.3496.
Exact Nonequilibrium Transport in the Topological Kondo Effect
Béri, B.
2017-07-01
A leading candidate for the experimental confirmation of the nonlocal quantum dynamics of Majorana fermions is the topological Kondo effect, predicted for mesoscopic superconducting islands connected to metallic leads. We identify an anisotropic, Toulouse-like, limit of the topological Kondo problem where the full nonequilibrium conductance and shot noise can be calculated exactly. Near the Kondo fixed point, we find novel asymptotic features including a universal conductance scaling function and fractional charge quantization observable via the Fano factor. In the universal regime, our results apply for generic anisotropy and even away from the Kondo limit as long as the system supports an emergent topological Kondo fixed point. Our approach thus provides key new qualitative insights and exact expressions for quantitative comparisons to future experimental data.
Kondo Effect in a Single Electron Transistor
Goldhaber-Gordon, David
1998-03-01
When a field-effect transistor is made very small, and electrons in the channel are separated from those in the leads by tunnel junctions, the transistor turns on and off every time an extra electron is added to the channel. The droplet of electrons confined in the channel of such a single-electron transistor (SET) interacts with electrons in the leads. This is in close analogy to an impurity atom interacting with the delocalized electrons in a metal, the traditional system for studying the Kondo effect.(Y. Meir, N.S. Wingreen, and P.A. Lee. PRL) 70, 2601 (1993) I will discuss measurements on a new generation of SETs that display all the aspects of the Kondo effect:(D. Goldhaber-Gordon, Hadas Shtrikman, D. Mahalu, D. Abusch-Magder, U. Meirav, and M.A. Kastner. To be published in Nature). a spin singlet forms between a localized electron in the channel and delocalized electrons in the leads, causing an enhancement of the zero-bias conductance, when the number of electrons on the artificial atom is odd but not when it is even. The system can be studied out of equilibrium by applying a voltage between the two leads, an impossible procedure in bulk Kondo systems. The spin singlet is altered by applying such a voltage or a magnetic field or by increasing the temperature, all in ways that agree with predictions. In addition, the tunability of an SET allows study of the system over a range of parameters not easily accessible to previous calculations or experiments.
Entanglement Entropy in a Holographic Kondo Model
Erdmenger, Johanna; Hoyos, Carlos; Newrzella, Max-Niklas; Wu, Jackson M S
2015-01-01
We calculate entanglement and impurity entropies in a recent holographic model of a magnetic impurity interacting with a strongly coupled system. There is an RG flow to an IR fixed point where the impurity is screened, leading to a decrease in impurity degrees of freedom. This information loss corresponds to a volume decrease in our dual gravity model, which consists of a codimension one hypersurface embedded in a BTZ black hole background in three dimensions. There are matter fields defined on this hypersurface which are dual to Kondo field theory operators. In the large N limit, the formation of the Kondo cloud corresponds to the condensation of a scalar field. The entropy is calculated according to the Ryu-Takayanagi prescription. This requires to determine the backreaction of the hypersurface on the BTZ geometry, which is achieved by solving the Israel junction conditions. We find that the larger the scalar condensate gets, the more the volume of constant time slices in the bulk is reduced, shortening the...
Kondo effect and mesoscopic ﬂuctuations
Indian Academy of Sciences (India)
Denis Ullmo; Sébastien Burdin; Dong E Liu; Harold U Baranger
2011-11-01
Two important themes in nanoscale physics in the last two decades are correlations between electrons and mesoscopic ﬂuctuations. Here we review our recent work on the intersection of these two themes. The setting is the Kondo effect, a paradigmatic example of correlated electron physics, in a nanoscale system with mesoscopic ﬂuctuations; in particular, we consider a small quantum dot coupled to a ﬁnite reservoir (which itself may be a large quantum dot). We discuss three aspects of this problem. First, in the high-temperature regime, we argue that a Kondo temperature K which takes into account the mesoscopic ﬂuctuations is a relevant concept: for instance, physical properties are universal functions of /K. Secondly, when the temperature is much less than the mean level spacing due to conﬁnement, we characterize a natural cross-over from weak to strong coupling. This strong coupling regime is itself characterized by well-deﬁned single-particle levels, as one can see from a Nozières Fermi-liquid theory argument. Finally, using a mean-ﬁeld technique, we connect the mesoscopic ﬂuctuations of the quasiparticles in the weak coupling regime to those at strong coupling.
Kondo effect in organometallic complexes with vibrating ligand shells
Energy Technology Data Exchange (ETDEWEB)
Kiselev, M.N. [Institut fuer Theoretische Physik und Astrophysik, Universitaet Wuerzburg, 97074 (Germany)]. E-mail: kiselev@physik.uni-wuerzburg.de; Kikoin, K. [Physics Department, Ben-Gurion University, Beer-Sheva 84105 (Israel); Wegewijs, M.R. [Institut fuer Theoretische Physik-Lehrstuhl A, RWTH Aachen, 52056 Aachen (Germany)
2007-03-15
We investigate transport through a mononuclear rare-earth metal-organic shell complex with strong tunnel coupling between the shell and two electrodes. The ground state of this molecule is a singlet while the first excited state is a triplet. We show that modulation of the tunnel barrier due to a molecular distortion which couples to the tunneling induces the Kondo effect, provided the discrete vibrational energy compensates the singlet/triplet gap. We discuss also the possibility of tuning the phonon-induced Kondo tunneling by external magnetic field and the finite bias Kondo anomaly.
Two-Channel Satellite Retrievals of Aerosol Properties: An Overview
Mishchenko, Michael I.
1999-01-01
In order to reduce current uncertainties in the evaluation of the direct and indirect effects of tropospheric aerosols on climate on the global scale, it has been suggested to apply multi-channel retrieval algorithms to the full period of existing satellite data. This talk will outline the methodology of interpreting two-channel satellite radiance data over the ocean and describe a detailed analysis of the sensitivity of retrieved aerosol parameters to the assumptions made in different retrieval algorithms. We will specifically address the calibration and cloud screening issues, consider the suitability of existing satellite data sets to detecting short- and long-term regional and global changes, compare preliminary results obtained by several research groups, and discuss the prospects of creating an advanced retroactive climatology of aerosol optical thickness and size over the oceans.
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.
Nonequilibrium electron transport through quantum dots in the Kondo regime
DEFF Research Database (Denmark)
Wölfle, Peter; Paaske, Jens; Rosch, Achim
2005-01-01
Electron transport at large bias voltage through quantum dots in the Kondo regime is described within the perturbative renormalization group extended to nonequilibrium. The conductance, local magnetization, dynamical spin susceptibility and local spectral function are calculated. We show how the ...
Quantum Entanglement in the Two Impurity Kondo Model
Cho, S Y; Cho, Sam Young; Kenzie, Ross H. Mc
2005-01-01
In order to quantify quantum entanglement in two impurity Kondo systems, we calculate the concurrence, negativity, and von Neumann entropy. The entanglement of the two Kondo impurities is shown to be determined by two competing many-body effects, the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, $I$. Due to the spin-rotational invariance of the ground state, the concurrence and negativity are uniquely determined by the spin-spin correlation between the impurities. It is found that there exists a critical minimum value of the antiferromagnetic correlation between the impurity spins which is necessary for entanglement of the two impurity spins. The critical value is discussed in relation with the unstable fixed point in the two impurity Kondo problem. Specifically, at the fixed point there is no entanglement between the impurity spins. Entanglement will only be created (and quantum information processing (QIP) be possible) if the RKKY interaction exchange energy, $I$, is at least severa...
Schwinger boson approach to the fully screened Kondo model.
Rech, J; Coleman, P; Zarand, G; Parcollet, O
2006-01-13
We apply the Schwinger boson scheme to the fully screened Kondo model and generalize the method to include antiferromagnetic interactions between ions. Our approach captures the Kondo crossover from local moment behavior to a Fermi liquid with a nontrivial Wilson ratio. When applied to the two-impurity model, the mean-field theory describes the "Varma-Jones" quantum phase transition between a valence bond state and a heavy Fermi liquid.
Evidence of Kondo effect in organic radical nanoassemblies
Rashidi, Mohammad; Mullegger, Stefan; Fattinger, Michael; Koch, Reinhold
2012-02-01
The outstanding spatial resolution of low temperature (LT) scanning tunneling microscopy (STM) and spectroscopy (STS) enables to probe the frontier orbital electronic structure of single magnetic molecules and clusters adsorbed on substrates. Here, we study self-aligned nanostructures of (spin-1/2) hydrocarbon radicals on a metal surface by means of LT-STM and STS. Pronounced involvement of surface state electrons is observed in the frontier molecular orbital (MO) resonances. An empty hybrid state closely above the substrate Fermi level exhibits the characteristic properties of surface Kondo effect reported for similar systems in the literature. By identifying three electronic states as hybrids of molecular orbitals and surface state electrons (two of them directly related to the Kondo effect), we are able to present a modified picture of the surface Kondo effect. It is based on a valence-bond model, where the bonding state represents Kondo's virtual bound state and the antibonding state is the so called 'Kondo resonance' reported in STM studies of the surface Kondo effect. Furthermore, double occupation of the originally singly unoccupied MO by tunneling electrons leads to the third state well above the Fermi level due to Coulomb repulsion as described by the Anderson model.
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.
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.
Tuning the Kondo effect in YbRh{sub 2}Si{sub 2}: Electron spin resonance under pressure and doping
Energy Technology Data Exchange (ETDEWEB)
Wykhoff, Jan; Sichelschmidt, J.; Krellner, C.; Geibel, C.; Steglich, F. [MPl for Chemical Physics of Solids, Dresden (Germany); Zakharov, D.V.; Krug von Nidda, H.A.; Loidl, A. [EP V, EKM, University of Augsburg (Germany); Fazlizhanov, I. [E.K. Zavoisky Physical Technical Institute, Kazan (Russian Federation)
2009-07-01
The observation of a well defined Electron Spin Resonance (ESR) signal below the Kondo temperature T{sub K} in the heavy-fermion compound YbRh{sub 2}Si{sub 2} refutes a common believe that concentrated rare earth ions in Kondo-lattice intermetallic compounds would be ESR silent in the Kondo regime. The signal shows distinct properties of the Yb{sup 3+} 4f spin and, hence, should contain valuable microscopic information on the dynamical Kondo coupling to the conduction electrons. We investigated the effect of tuning the 4f - conduction electron hybridization strength by Co-doping and hydrostatic pressure up to 3 GPa. Both stabilize antiferromagnetic order, lead to a reduction of T{sub K}, and yield pronounced changes in the ESR parameters. By comparing the quantitatively different effect of pressure and Co doping on the ESR parameters we found a relation of the zero temperature residual ESR linewidth to the residual resistivity and the linear in temperature slope of the linewidth as was similarly reported for the La-doping case.
Kondo effect at low electron density and high particle-hole asymmetry in 1D, 2D, and 3D
Žitko, Rok; Horvat, Alen
2016-09-01
Using the perturbative scaling equations and the numerical renormalization group, we study the characteristic energy scales in the Kondo impurity problem as a function of the exchange coupling constant J and the conduction-band electron density. We discuss the relation between the energy gain (impurity binding energy) Δ E and the Kondo temperature TK. We find that the two are proportional only for large values of J , whereas in the weak-coupling limit the energy gain is quadratic in J , while the Kondo temperature is exponentially small. The exact relation between the two quantities depends on the detailed form of the density of states of the band. In the limit of low electron density the Kondo screening is affected by the strong particle-hole asymmetry due to the presence of the band-edge van Hove singularities. We consider the cases of one- (1D), two- (2D), and three-dimensional (3D) tight-binding lattices (linear chain, square lattice, cubic lattice) with inverse-square-root, step-function, and square-root onsets of the density of states that are characteristic of the respective dimensionalities. We always find two different regimes depending on whether TK is higher or lower than μ , the chemical potential measured from the bottom of the band. For 2D and 3D, we find a sigmoidal crossover between the large-J and small-J asymptotics in Δ E and a clear separation between Δ E and TK for TKband edge. Furthermore, we find that in 1D the particle-hole asymmetry leads to a large decrease of TK compared to the standard result obtained by approximating the density of states to be constant (flat-band approximation), while in 3D the opposite is the case; this is due to the nontrivial interplay of the exchange and potential scattering renormalization in the presence of particle-hole asymmetry. The 2D square-lattice density of states behaves to a very good approximation as a band with constant density of states.
How does a Kondo impurity respond to its local environment?
Heinrich, Andreas
2008-03-01
The interplay between localized electrons on a magnetic atom and the conducting electrons in a metal can lead to intriguing many-body ground states such as the Kondo effect. When a spin is Kondo screened by conduction electrons the entire spin system performs a complicated dance that results in the formation of a spin singlet at sufficiently low temperature. For simplicity, most theoretical considerations of Kondo screening focus on magnetic impurities with the lowest possible spin S = 1/2. Such systems can be studied experimentally in exquisite detail and with great control using quantum dots in semiconductor heterostructures or carbon nanotubes. However, in Kondo systems consisting of localized magnetic atoms, the spin is often larger, making the Kondo effect richer and more complex. Here we use the imaging and spectroscopy capabilities of a scanning tunnelling microscope to study how the Kondo screening of a known high-spin atom is determined by its local environment. Co and Ti atoms were deposited on a thin insulating layer (Cu2N) on a copper substrate. We study the influence of external magnetic fields, crystalline magnetic anisotropy, as well as spin-coupling to surrounding atomic spins on the Kondo effect that forms on the Co or Ti atoms. We find that the anisotropy of the crystalline field quenches the high-spin system of Co (S = 3/2) into an effective S = 1/2 Kramers doublet. Surprisingly, much of the impact of these environmental factors on the complex many-body ground state can be understood simply through their effects on the energy levels of the unscreened spin.
Interfacial phase competition induced Kondo-like effect in manganite-insulator composites
Lin, Ling-Fang; Wu, Ling-Zhi; Dong, Shuai
2016-12-01
A Kondo-like effect, namely, the upturn of resistivity at low temperatures, is observed in perovskite manganite when nonmagnetic insulators are doped as secondary phase. In this paper, the low-temperature resistivity upturn effect has been argued to originate from interfacial magnetic phase reconstruction. Heisenberg spin lattices have been simulated using the Monte Carlo method to reveal phase competition around secondary phase boundary, namely, manganite-insulator boundary that behaves with a weak antiferromagnetic tendency. Moreover, the resistor network model based on double-exchange conductive mechanism reproduces the low-temperature resistivity upturn effect. Our work provides a reasonable physical mechanism to understand the novel transport behaviors in microstructures of correlated electron systems.
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.
AC Conductance Through a Vibrating Molecular Dot in Kondo Regime
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
In the present paper, by applying the Lang-Firsov canonical transformation and the so-called non-crossing approximation technique, we investigate the joint effects of the electron-phonon interaction and an external alternating gate voltage on the transport of a quantum dot system in the Kondo regime. We find that, while the satellite Kondo resonant peaks appear in both the averaged local density of states and the differential conductance, the main Kondo peak at the Fermi energy is greatly suppressed. These results confirm the previous ones derived by other methods, such as the equation of motion solution. Furthermore, based on the picture of virtual transition between quasi-eigenstates in the system, we also give a slightly different explanation on these phenomena.
Surface Kondo Impurities in the Slave-Boson Approach
Anda, Enrique; Vernek, Edson
2005-03-01
Transport properties of magnetic impurities on surfaces have captured a great deal of attention lately. Atom manipulation and topographic imaging techniques using scanning tunneling microscope have confirmed some theoretical predictions on Kondo physics and at the same time revealed other interesting behavior in these systems. For example, experiments have reported unexpectedly high Kondo temperatures for multi-impurity and molecular structures on metallic surfaces. Motivated by these experimental results we apply slave boson techniques for finite Coulomb interaction (finite U) to study the transport properties of magnetic impurities on a metallic surface in the Kondo regime. We report here on our studies of the role of fluctuations on the slave boson number for the case of one impurity on metallic surfaces. We compare our results to other theoretical approaches and to experimental results. Supported by CAPES-Brazil and NSF-IMC and NSF-NIRT.
Hydrogen-induced Kondo effect for Co/Pt(111)
Energy Technology Data Exchange (ETDEWEB)
Dubout, Quentin; Calleja Mitja, Fabian; Etzkorn, Markus; Lehnert, Anne; Claude, Laurent; Gambardella, Pietro; Brune, Harald [Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne (Switzerland)
2011-07-01
We present 0.4 K Scanning Tunneling Spectroscopy (STS) results on hydrogenated Co adatoms on Pt(111). Molecular H dosage creates two Co-H adsorption complexes with comparable abundance. Type I displays very large (40 %) inelastic conductance steps that originate from vibrations, as evidenced by their shift when substituting H by D. Type II displays smaller (5 %) conductance steps at higher energies, again due to H vibrations, together with a large conductance peak at the Fermi level. This feature is attributed to the Kondo effect. Its splitting in magnetic fields up to 8 Tesla identifies the Co-H complex as a S = 1/2 system, whereas clean Co/Pt(111) has a spin of 1 and shows no Kondo effect. H-adsorption has been reported to quench the Kondo effect, here we show that it can produce it.
Quadrupolar Kondo effect in uranium heavy-electron materials?
Cox, D. L.
1987-01-01
The possibility of an electric quadrupole Kondo effect for a non-Kramers doublet on a uranium (U) ion is a cubic metallic host is demonstrated by model calculations showing a Kondo upturn in the resistivity, universal quenching of the quadrupolar moment, and a heavy-electron anomaly in the electronic specific heat. With inclusion of excited crystal-field levels, some of the unusual magnetic-response data in the heavy-electron superconductor UBe13 may be understood. Structural phase transitions at unprecedented low temperatures may occur in U-based heavy-electron materials.
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
Kondo cloud of single heavy quark in cold and dense matter
Yasui, Shigehiro
2016-01-01
The Kondo effect is a universal phenomena observed in a variety of fermion systems containing a heavy impurity particle whose interaction is governed by the non-Abelian interaction. At extremely high density, I study the Kondo effect by color exchange in quark matter containing a single heavy (charm or bottom) quark as an impurity particle. To obtain the ground state with the Kondo effect, I introduce the condensate mixing the light quark and the heavy quark (Kondo cloud) in the mean-field approximation. I estimate the energy gain by formation of the Kondo cloud, and present that the Kondo cloud exhibits the resonant structure. I also evaluate the scattering cross section for the light quark and the heavy quark, and discuss its effect to the finite size quark matter.
Kondo cloud of single heavy quark in cold and dense matter
Yasui, Shigehiro
2017-10-01
The Kondo effect is a universal phenomena observed in a variety of fermion systems containing a heavy impurity particle whose interaction is governed by the non-Abelian interaction. At extremely high density, I study the Kondo effect by color exchange in quark matter containing a single heavy (charm or bottom) quark as an impurity particle. To obtain the ground state with the Kondo effect, I introduce the condensate mixing the light quark and the heavy quark (Kondo cloud) in the mean-field approximation. I estimate the energy gain by formation of the Kondo cloud, and present that the Kondo cloud exhibits the resonant structure. I also evaluate the scattering cross section for the light quark and the heavy quark, and discuss its effect to the finite size quark matter.
Kondo effect of D\\xAFs and D\\xAFs* mesons in nuclear matter
Yasui, Shigehiro; Sudoh, Kazutaka
2017-03-01
We study the Kondo effect for D¯s and D¯s* mesons as impurity particles in nuclear matter. The spin-exchange interaction between the D¯s or D¯s* meson and the nucleon induces the enhancement of the effective coupling in the low-energy scattering in the infrared region, whose energy scale of singularity is given by the Kondo scale. We investigate the Kondo scale in the renormalization group equation at nucleon one-loop level. We furthermore study the ground state with the Kondo effect in the mean-field approach, and present that the Kondo scale is related to the mixing strength between the D¯s or D¯s* meson and the nucleon in nuclear matter. We show the spectral function of the impurity when the Kondo effect occurs.
On perturbation of eigenvalues embedded at thresholds in a two channel model
DEFF Research Database (Denmark)
Jensen, Arne
2002-01-01
We present some results on the perturbation of eigenvalues embedded at thresholds in a two channel model Hamiltonian with a small off-diagonal perturbation. Examples are given of the various types of behavior of the eigenvalue under perturbation....
On Perturbation of Eigenvalues Embedded at Thresholds in a Two Channel Model
Indian Academy of Sciences (India)
Arne Jensen
2002-02-01
We present some results on the perturbation of eigenvalues embedded at thresholds in a two channel model Hamiltonian with a small off-diagonal perturbation. Examples are given of the various types of behavior of the eigenvalue under perturbation.
Implementation of a Two-Channel Maximally Decimated Filter Bank using Switched Capacitor Circuits
Nahlik, J.; Hospodka, J.; P. Sovka; B. Psenicka
2013-01-01
The aim of this paper is to describe the implementation of a two-channel filter bank (FB) using the switched capacitor (SC) technique considering real properties of operational amplifiers (OpAmps). The design procedure is presented and key recommendations for the implementation are given. The implementation procedure describes the design of two-channel filter bank using an IIR Cauer filter, conversion of IIR into the SC filters and the final implementation of the SC filters. The whole design ...
Zhang, Jingdi; Yong, Jie; Takeuchi, Ichiro; Greene, Richard; Averitt, Richard
We utilize terahertz time domain spectroscopy to investigate thin films of the heavy fermion compound SmB6, 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 20K) indicates the emergence of a surface state with an effective electron mass of 0.1me. Conductivity dynamics following optical excitation are 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 20K, indicative of another channel opening up in the low energy electrodynamics. Taken together, these results suggest the onset of a surface state well below the crossover temperature (100K) after long-range coherence of the f-electron Kondo lattice is established. JZ and RDA acknowledge support from DOE - Basic Energy Sciences under Grant No. DE-FG02-09ER46643, under which the THz measurements and data analysis were performed. JY, IT and RLG acknowledge support from ONR N00014-13-1-0635 and NSF DMR 1410665.
Competition between Kondo and indirect exchange at the edges and bulk of graphene, and 2D materials
Allerdt, Andrew; Martins, George; Feiguin, Adrian
We study the problem of two magnetic impurities at the surface of graphene, BN, MoS2, phosphorene, silicene and germanene using exact numerical methods. We map the band structure of these materials onto one dimensional tight-binding chains in the same spirit as Wilson's numerical renormalization group. We use the density matrix renormalization group to solve the problem exactly, keeping all the information about the underlying lattice. Competition between Kondo and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions is non-trivial, due to strong non-perturbative effects. Depending on the presence of a pseudogap, or gap, we identify an important directionality and position dependence of the correlations. We present scenarios and regimes where impurities prefer to form their own Kondo clouds instead of an RKKY singlet state, or remain as uncoupled local moments. In the particular case of graphene, ferromagnetism is only stable at half-filling. In addition, we study the effects of spin-orbit coupling, and the presence of edge states.
The effect of Ce dilution on the ferromagnetic ordering and Kondo behavior of CeRuPO
Noorafshan, M.; Nourbakhsh, Z.
2017-03-01
The structural, electronic and magnetic properties and Kondo behavior of Ce1-xLax RuPO (x=0, 0.25, 0.5, 0.75 and 1) alloys are investigated using density functional theory by utilizing Wien2k package. The exchange-correlation potential is treated with the generalized gradient approximation (GGA). Moreover, the GGA+U approach (where U is the Hubbard correlation term) is employed to treat the f-electrons properly. We also present a comparative study between the electronic structure and magnetic properties of these alloys within GGA and GGA+U approaches. The calculated lattice parameters and bulk moduli of these alloys as a function of x are in the best agreement with Vegard's linear rule. The total and partial electron density of states and linear coefficient of electronic specific heat of these alloy within GGA and GGA+U are investigated and compared. The effect of La substitution on the Kondo behavior of CeRuPO compound is investigated.
Sinnecker, E. H. C. P.; Sant'Anna, M. M.; ElMassalami, M.
2017-02-01
We followed the evolution of the normal and superconducting properties of Al thin films after each session of various successive oxygen irradiations at ambient temperature. Such irradiated films, similar to the granular ones, exhibit enhanced superconductivity, Kondo behavior, and negative-curvature resistivity. Two distinct roles of oxygen are identified: as a damage-causing projectile and as an implanted oxidizing agent. The former gives rise to the processes involved in the conventional recovery stages. The latter, considered within the context of the Cabrera-Mott model, gives rise to a multistep process which involves charges transfer and creation of stabilized vacancies and charged defects. Based on the outcome of this multistep process, we consider (i) the negative-curvature resistivity as a manifestation of a thermally assisted liberation of trapped electric charges, (ii) the Kondo contribution as a spin-flip scattering from paramagnetic, color-center-type defects, and (iii) the enhancement of Tc as being due to a lattice softening facilitated by the stabilized defects and vacancies. The similarity in the phase diagrams of granular and irradiated films as well as the aging effects are discussed along the same line of reasoning.
Buot, Felix A.; Otadoy, Roland E. S.; Rivero, Karla B.
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.
Kondo screening of the spin and orbital magnetic moments of Fe impurities in Cu
Joly, L.; Kappler, J.-P.; Ohresser, P.; Sainctavit, Ph.; Henry, Y.; Gautier, F.; Schmerber, G.; Kim, D. J.; Goyhenex, C.; Bulou, H.; Bengone, O.; Kavich, J.; Gambardella, P.; Scheurer, F.
2017-01-01
We use x-ray magnetic circular dichroism to evidence the effect of correlations on the local impurity magnetic moment in an archetypal Kondo system, namely, a dilute Cu:Fe alloy. Applying the sum rules on the Fe L2 ,3 absorption edges, the evolution of the spin and orbital moments across the Kondo temperature are determined separately. The spin moment presents a crossover from a nearly temperature-independent regime below the Kondo temperature to a paramagneticlike regime above. Conversely, the weak orbital moment shows a temperature-independent behavior in the whole temperature range, suggesting different Kondo screening temperature scales for the spin and orbital moments.
Chakrabarti, J; Bagchi, B; Chakrabarti, Jayprokas; Basu, Asis; Bagchi, Bijon
2000-01-01
Fermions on the lattice have bosonic excitations generated from the underlying periodic background. These, the lattice bosons, arise near the empty band or when the bands are nearly full. They do not depend on the nature of the interactions and exist for any fermion-fermion coupling. We discuss these lattice boson solutions for the Dirac Hamiltonian.
Kondo effect for electron transport through an artificial quantum dot
Institute of Scientific and Technical Information of China (English)
Sun Ke-Wei; Xiong Shi-Jie
2006-01-01
We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper.We obtain the conductance for the system of a quantum dot which is embedded in a one-dimensional chain in zero and finite temperature cases.The external magnetic field gives rise to a negative magnetoconductance in the zero temperature case.It increases as the external magnetic field increases.We obtain the relation between the coupling coefficient and conductance.If the interaction is big enough to prevent conduction electrons from tunnelling through the dot,the dispersion effect is dominant in this case.In the Kondo temperature regime,we obtain the conductivity of a quantum dot system with Kondo correlation.
Characterization of a correlated topological Kondo insulator in one dimension
Hagymási, I.; Legeza, Ö.
2016-04-01
We investigate the ground state of a p -wave Kondo-Heisenberg model introduced by Alexandrov and Coleman with an Ising-type anisotropy in the Kondo interaction and correlated conduction electrons. Our aim is to understand how they affect the stability of the Haldane state obtained in the SU(2)-symmetric case without the Hubbard interaction. By applying the density-matrix renormalization group algorithm and calculating the entanglement entropy we show that in the anisotropic case a phase transition occurs and a Néel state emerges above a critical value of the Coulomb interaction. These findings are also corroborated by the examination of the entanglement spectrum and the spin profile of the system which clarify the structure of each phase.
Kondo-effect of substitutional cobalt impurities at copper surfaces
Energy Technology Data Exchange (ETDEWEB)
Wahl, P; Diekhoener, L; Schneider, M A; Kern, K [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstr. 1, D-70569 Stuttgart (Germany); Seitsonen, A P [IMPMC, CNRS and Universite Pierre et Marie Curie, 4 Place Jussieu, Case 115, F-75252 Paris (France)], E-mail: wahl@fkf.mpg.de
2009-11-15
The influence of the coordination on the Kondo temperature of a magnetic impurity at a noble metal surface and the line shape observed in low temperature scanning tunneling spectroscopy (STS) is investigated for single cobalt atoms adsorbed on and embedded in copper surfaces. Surprisingly, the Kondo temperature for substitutional cobalt atoms is almost the same as that of adatoms on the Cu(100) surface. This is in stark contrast to the behaviour observed at the Cu(111) surface. DFT calculations reveal that in the case of Cu(100) the coupling of the spin of the cobalt atom to the conduction band is not substantially increased by the incorporation of the cobalt atom. At the same time the observed line shape differs strongly from what is observed on adatom systems.
Tunable Kondo Effect of a Three-Terminal Transport Quantum Dot Embedded in an Aharonov-Bohm Ring
Institute of Scientific and Technical Information of China (English)
CHEN Xiong-Wen; SHI Zhen-Gang; WU Shao-Quan; SONG Ke-Hui
2006-01-01
@@ We theoretically investigate the Kondo effect of a three-terminal transport quantum dot (QD) embedded in an Aharonov-Bohm ring in the Kondo regime by means of the one-impurity Anderson Hamiltonian.
Conductance fingerprint of Majorana fermions in the topological Kondo effect
Galpin, Martin R.; Mitchell, Andrew K.; Temaismithi, Jesada; Logan, David E.; Béri, Benjamin; Cooper, Nigel R.
2014-01-01
We consider an interacting nanowire/superconductor heterostructure attached to metallic leads. The device is described by an unusual low-energy model involving spin-1 conduction electrons coupled to a nonlocal spin-1/2 Kondo impurity built from Majorana fermions. The topological origin of the resulting Kondo effect is manifest in distinctive non-Fermi-liquid (NFL) behavior, and the existence of Majorana fermions in the device is demonstrated unambiguously by distinctive conductance line shapes. We study the physics of the model in detail, using the numerical renormalization group, perturbative scaling, and Abelian bosonization. In particular, we calculate the full scaling curves for the differential conductance in ac and dc fields, onto which experimental data should collapse. Scattering t matrices and thermodynamic quantities are also calculated, recovering asymptotes from conformal field theory. We show that the NFL physics is robust to asymmetric Majorana-lead couplings, and here we uncover a duality between strong and weak coupling. The NFL behavior is understood physically in terms of competing Kondo effects. The resulting frustration is relieved by inter-Majorana coupling which generates a second crossover to a regular Fermi liquid.
Thermopower of few-electron quantum dots with Kondo correlations
Ye, Lvzhou
2015-03-01
The thermopower of few-electron quantum dots is crucially influenced by on-dot electron-electron interactions, particularly in the presence of Kondo correlations. We present a comprehensive picture which elucidates the underlying relations between the thermopower and the spectral density function of two-level quantum dots. The effects of various electronic states, including the Kondo states originating from both spin and orbital degrees of freedom, are clearly unraveled. With these insights, we have exemplified an effective and viable way to control the sign of thermopower of Kondo-correlated quantum dots. This is realized by tuning the temperature and by selecting the appropriate level spacing and Coulomb repulsion strength. Such a physical picture is affirmed by accurate numerical data obtained with a hierarchical equations of motion approach. Our understandings and findings provide useful insights into controlling the direction of electric (heat) current through a quantum dot by applying a temperature (voltage) gradient across the two coupling leads. This may have important implications for novel thermoelectric applications of quantum dots. The support from the Natural Science Foundation of China (Grants No. 21033008, No. 21233007, No. 21303175, and No. 21322305) and the Strategic Priority Research Program (B) of the CAS (XDB01020000) is gratefully appreciated.
Observation of the frozen charge of a Kondo resonance
Desjardins, M. M.; Viennot, J. J.; Dartiailh, M. C.; Bruhat, L. E.; Delbecq, M. R.; Lee, M.; Choi, M.-S.; Cottet, A.; Kontos, T.
2017-04-01
The ability to control electronic states at the nanoscale has contributed to our modern understanding of condensed matter. In particular, quantum dot circuits represent model systems for the study of strong electronic correlations, epitomized by the Kondo effect. We use circuit quantum electrodynamics architectures to study the internal degrees of freedom of this many-body phenomenon. Specifically, we couple a quantum dot to a high-quality-factor microwave cavity to measure with exceptional sensitivity the dot’s electronic compressibility, that is, its ability to accommodate charges. Because electronic compressibility corresponds solely to the charge response of the electronic system, it is not equivalent to the conductance, which generally involves other degrees of freedom such as spin. Here, by performing dual conductance and compressibility measurements in the Kondo regime, we uncover directly the charge dynamics of this peculiar mechanism of electron transfer. The Kondo resonance, visible in transport measurements, is found to be ‘transparent’ to microwave photons trapped in the high-quality cavity, thereby revealing that (in such a many-body resonance) finite conduction is achieved from a charge frozen by Coulomb interaction. This freezing of charge dynamics is in contrast to the physics of a free electron gas. We anticipate that the tools of cavity quantum electrodynamics could be used in other types of mesoscopic circuits with many-body correlations, providing a model system in which to perform quantum simulation of fermion-boson problems.
Kondo hybridisation and the origin of metallic states at the (001) surface of SmB6
E. Frantzeskakis; N. de Jong; B. Zwartsenberg; Y.K. Huang; Y. Pan; X. Zhang; F.X. Zhang; L.H. Bao; O. Tegus; A. Varykhalov; A. de Visser; M. Golden
2013-01-01
SmB6, a well-known Kondo insulator, has been proposed to be an ideal topological insulator with states of topological character located in a clean, bulk electronic gap, namely, the Kondo-hybridization gap. Since the Kondo gap arises from many-body electronic correlations, SmB6 would be placed at the
Kondo hybridisation and the origin of metallic states at the (001) surface of SmB6
Frantzeskakis, E.; de Jong, N.; Zwartsenberg, B.; Huang, Y.K.; Pan, Y.; Zhang, X.; Zhang, F.X.; Bao, L.H.; Tegus, O.; Varykhalov, A.; de Visser, A.; Golden, M.
2013-01-01
SmB6, a well-known Kondo insulator, has been proposed to be an ideal topological insulator with states of topological character located in a clean, bulk electronic gap, namely, the Kondo-hybridization gap. Since the Kondo gap arises from many-body electronic correlations, SmB6 would be placed at the
Phonon-assisted and magnetic field induced Kondo tunneling in single molecular devices
Energy Technology Data Exchange (ETDEWEB)
Kikoin, K [School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel); Kiselev, M N [The Abdus Salam International Centre for Theoretical Physics, Trieste (Italy)
2007-12-15
We consider the Kondo tunneling induced by multiphonon emission/absorption processes in magnetic molecular complexes with low-energy singlet-triplet spin gap and show that the number of assisting phonons may be changed by varying the Zeeman splitting of excited triplet state. As a result, the structure of multiphonon Kondo resonances may be scanned by means of magnetic field tuning.
A Two-Channel Training Algorithm for Hidden Markov Model and Its Application to Lip Reading
Directory of Open Access Journals (Sweden)
Yong Lian
2005-06-01
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.
An experimental evaluation of a loop versus a reference design for two-channel microarrays
Vinciotti, V.; Khanin, R.; Alimonte, D. D’; Liu, X.; Cattini, N.; Hotchkiss, G.; Bucca, G.; Jesus, O. de; Rasaiyaah, J.; Kellam, P.; Wit, Ernst
2005-01-01
Motivation: Despite theoretical arguments that so-called ‘loop designs’ for two-channel DNA microarray experiments are more efficient, biologists continue to use ‘reference designs’. We describe two sets of microarray experiments with RNA from two different biological systems (TPA-stimulated mammali
Assessment of a two-channel implantable peroneal nerve stimulator post-stroke
Kottink, A.I.R.
2010-01-01
Thesis outline and aims: to progress towards evidence based application of PNS to improve lower extremity function, the aim of the present thesis is to evaluate an implantable two-channel peroneal nerve stimulator versus conventional splinting as a treatment option for chronic stroke patients with a
Wang, Da-Wei; Zhu, Shi-Yao; Scully, Marlan O
2014-01-01
We show that the timed Dicke states of a collection of three-level atoms can form a tight-binding lattice in the momentum space. This lattice, coined the superradiance lattice (SL), can be constructed based on an electromagnetically induced transparency (EIT) system. For a one-dimensional SL, we need the coupling field of the EIT system to be a standing wave. The detuning between the two components of the standing wave introduces an effective electric field. The quantum behaviours of electrons in lattices, such as Bloch oscillations, Wannier-Stark ladders, Bloch band collapsing and dynamic localization can be observed in the SL. The SL can be extended to two, three and even higher dimensions where no analogous real space lattices exist and new physics are waiting to be explored.
Effect of two-channel gastric electrical stimulation with trains of pulses on gastric motility
Institute of Scientific and Technical Information of China (English)
Bin Yang; Xiao-Hua Hou; Geng-Qing Song; Jin-Song Liu; Jiande DZ Chen
2009-01-01
AIM: To investigate the effect of two-channel gastric electrical stimulation (GES) with trains of pulses on gastric emptying and slow waves. METHODS: Seven dogs implanted with four pairs of electrodes and equipped with a duodenal cannula were involved in this study. Two experiments were performed. The first experiment included a series of sessions in the fasting state with trains of short or long pulses, each lasted 10 min. A 5-min recording without pacing was made between two sessions. The second experiment was performed in three sessions (control, single-channel GES, and two-channel GES). The stimulus was applied via the 1st pair of electrodes for single-channel GES (GES via one pair of electrodes located at 14 cm above the pylorus), and simultaneously via the 1st and 3rd channels for two-channel GES (GES via two pairs of electrodes located at 6 and 14 cm above the pylorus). Gastric liquid emptying was collected every 15 min via the cannula for 90 min. RESULTS: GES with trains of pulses at a pulse width of 4 ms or higher was able to entrain gastric slow waves. Two-channel GES was about 50% more efficient than single-channel GES in entraining gastric slow waves. Two channel but not single-channel GES with trains of pulses was capable of accelerating gastric emptying in healthy dogs. Compared with the control session, two-channel GES significantly increased gastric emptying of liquids at 15 min (79.0% ± 6.4% vs 61.3% ± 6.1%, P < 0.01), 30 min (83.2% ± 6.3 % vs 68.2% ± 6.9%, P < 0.01),60 min (86.9% ± 5.5 % vs 74.1% ± 5.9%, P < 0.01),and 90 min (91.0% ± 3.4% vs 76.5% ± 5.9%, P < 0.01).CONCLUSION: Two-channel GES with trains of pulses accelerates gastric emptying in healthy dogs and may have a therapeutic potential for the treatment of gastric motility disorders.
Influence of local spin polarization to the Kondo effect
Institute of Scientific and Technical Information of China (English)
LI Huan; GUO Wei
2007-01-01
We use the spin non-degenerate single impurity Anderson model to investigate the influence of the local spin polarization to the Kondo effect. By using the Schrieffer-Wolff transformation, we obtain a generalized s-d exchange Hamiltonian, which describes the interaction between a polarized local spin and conduction electrons. In this case, the singlet is no longer an eigenstate as shown by variational calculations where the splitting of the local energy △= εd↑ - εd↓ can be arbitrarily small. The local spin polarization generates the instability of the singlet ground state of the S = 1/2 s-d exchange model.
Non-equilibrium Kondo effect in double quantum dot
Energy Technology Data Exchange (ETDEWEB)
Kiselev, M.N. E-mail: kiselev@physik.uni-wuerzburg.de; Kikoin, K.A.; Molenkamp, L.W
2004-05-01
We investigate theoretically a non-equilibrium transport through a double quantum dot (DQD) in a parallel geometry. It is shown that the resonance Kondo tunneling through a parallel DQD with even occupation and singlet ground state may arise at a strong bias, which compensates the energy of singlet/triplet excitation. Using the renormalization group technique we derive scaling equations and calculate the differential conductance as a function of an auxiliary DC-bias for parallel DQD being in a regime described by SO(4) symmetry.
Photoexcited electron dynamics in Kondo insulators and heavy fermions
Demsar, Jure; Thorsmolle, Verner K.; Sarrao, John L.; Taylor, Antoinette J.
2005-01-01
We have studied the photoexcited carrier relaxation dynamics in the Kondo insulator SmB6 and the heavy fermion metal YbAgCu4 as a function of temperature and excitation level. The dynamic response is found to be both strongly temperature dependent and nonlinear. The data are analyzed with a Rothwarf-Taylor bottleneck model, where the dynamics are governed by the presence of a narrow gap in the density of states near the Fermi level. The remarkable agreement with the model suggests that carrie...
Local Moment Formation and Kondo Effect in Defective Graphene
Cazalilla, M. A.; Iucci, A.; Guinea, F.; Neto, A. H. Castro
2012-01-01
We study the local moment formation and the Kondo effect at single-atom vacancies in Graphene. We develop a model accounting for the vacancy reconstruction as well as non-planarity effects induced by strain and/or temperature. Thus, we find that the dangling $\\sigma$ orbital localized at the vacancy is allowed to strongly hybridize with the $\\pi$-band since the scattering with the vacancy turns the hybridization into singular function of the energy ($\\sim [|\\epsilon| \\ln^2 \\epsilon/D]^{-1}$, ...
Holographic optical traps for atom-based topological Kondo devices
Buccheri, F.; Bruce, G. D.; Trombettoni, A.; Cassettari, D.; Babujian, H.; Korepin, V. E.; Sodano, P.
2016-07-01
The topological Kondo (TK) model has been proposed in solid-state quantum devices as a way to realize non-Fermi liquid behaviors in a controllable setting. Another motivation behind the TK model proposal is the demand to demonstrate the quantum dynamical properties of Majorana fermions, which are at the heart of their potential use in topological quantum computation. Here we consider a junction of crossed Tonks-Girardeau gases arranged in a star-geometry (forming a Y-junction), and we perform a theoretical analysis of this system showing that it provides a physical realization of the TK model in the realm of cold atom systems. Using computer-generated holography, we experimentally implement a Y-junction suitable for atom trapping, with controllable and independent parameters. The junction and the transverse size of the atom waveguides are of the order of 5 μm, leading to favorable estimates for the Kondo temperature and for the coupling across the junction. Since our results show that all the required theoretical and experimental ingredients are available, this provides the demonstration of an ultracold atom device that may in principle exhibit the TK effect.
Multiterminal Conductance and Decoherence Effect of a Three-Terminal Kondo Dot
Institute of Scientific and Technical Information of China (English)
FANG Tie-Feng; WANG Shun-Jin
2006-01-01
@@ A three-terminal Kondo dot modelled by the Anderson Hamiltonian is investigated. In the strong correlation limit, we calculate the multiterminal conductance and the voltage-induced characteristic splitting of the nonequilibrium Kondo resonance by using the equation of motion approach from viewpoint of the correlation dynamics.A qualitative and reasonable agreement with a recently reported experiment is obtained. We also simulate phenomenologically the decoherence of the Kondo-coherent state formed in the two-terminal setup in the framework of our three-terminal model.
An experimental evaluation of a loop versus a reference design for two-channel microarrays
2005-01-01
http://bioinformatics.oxfordjournals.org/cgi/content/abstract/21/4/492 Motivation: Despite theoretical arguments that socalled \\loop designs" of two-channel DNA microarray experiments are more e cient, biologists keep on using \\reference designs". We describe two sets of microarray experiments with RNA from two di erent biological systems (TPA-stimulated mammalian cells and Streptomyces coelicor). In each case, both a loop and a reference design were performed using the same RNA preparatio...
Majorana bound states in two-channel time-reversal-symmetric nanowire systems
DEFF Research Database (Denmark)
Gaidamauskas, Erikas; Paaske, Jens; Flensberg, Karsten
2014-01-01
must be negative, 2) inversion symmetry must be broken, and 3) the two channels must have different spin-orbit couplings. For the case of collinear spin-orbit directions, we find a general expression for the topological invariant by block diagonalization into two blocks with chiral symmetry only....... By projection to the low-energy sector we solve for the zero modes explicitly and study the details of the gap closing, which in the general case happens at finite momenta....
On the interplay between heavy-fermion and soft crystal field excitations in Kondo lattices
Energy Technology Data Exchange (ETDEWEB)
Kagan, Yu.; Kikoin, K.A.; Mishchenko, A.S. [Rossijskij Nauchnyj Tsentr ``Kurchatovskij Inst.``, Moscow (Russian Federation)
1997-06-13
On the grounds of the microscopic theory of heavy-fermion spin-liquids a novel description of low-energy excitation spectra in CeNiSn and related compounds is offered. The anomalous properties of orthorhombic CeNiSn and related materials are explained by the interplay between the fermi-type spinon excitations with the energy scale T{sup *}{approx}T{sub K} and the one-site crystal field excitations with the energy {Delta}{sub CF}
Venegas, P. A.; Garcia, F. A.; Garcia, D. J.; Cabrera, G. G.; Avila, M. A.; Rettori, C.
2016-12-01
Recent experiments on G d3 + electron-spin resonance (ESR) in the filled skutterudite C e1 -xG dxF e4P12(x ≈0.001 ) , at temperatures where the host resistivity manifests a smooth insulator-metal crossover, provide evidence of the underlying Kondo physics associated with this system. At low temperatures (below T ≈160 K), C e1 -xG dxF e4P12 behaves as a Kondo insulator with a relatively large hybridization gap, and the G d3 + ESR spectra display a fine structure with Lorentzian line shape, typical of insulating media. In this work, based on previous experiments performed by the same group, we argue that the electronic gap may be attributed to the large hybridization present in the coherent regime of a Kondo lattice. Moreover, mean-field calculations suggest that the electron-phonon interaction is fundamental at explaining such hybridization. The resulting electronic structure is strongly temperature dependent, and at T*≈160 K the system undergoes an insulator-to-metal transition induced by the withdrawal of 4 f electrons from the Fermi volume, the system becoming metallic and nonmagnetic. The G d3 + ESR fine structure coalesces into a single Dysonian resonance, as in metals. Our simulations suggest that exchange narrowing via the usual Korringa mechanism is not enough to describe the thermal behavior of the G d3 + ESR spectra in the entire temperature region (4.2-300 K). We propose that the temperature activated fluctuating valence of the Ce ions is the key ingredient that fully describes this unique temperature dependence of the G d3 + ESR fine structure.
Gate-controlled Kondo screening in graphene: Quantum criticality and electron-hole asymmetry
Vojta, M.; Fritz, L.; Bulla, R.
2010-04-01
Magnetic impurities in neutral graphene provide a realization of the pseudogap Kondo model, which displays a quantum phase transition between phases with screened and unscreened impurity moment. Here, we present a detailed study of the pseudogap Kondo model with finite chemical potential μ. While carrier doping restores conventional Kondo screening at lowest energies, properties of the quantum critical fixed point turn out to influence the behavior over a large parameter range. Most importantly, the Kondo temperature TK shows an extreme asymmetry between electron and hole doping. At criticality, depending on the sign of μ, TK follows either the scaling prediction TK~|μ| with a universal prefactor, or TK~|μ|x with x≈2.6. This asymmetry between electron and hole doping extends well outside the quantum critical regime and also implies a qualitative difference in the shape of the tunneling spectra for both signs of μ.
Energy Technology Data Exchange (ETDEWEB)
Maiti, Kalobaran; Patil, Swapnil; Adhikary, Ganesh [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005 (India); Balakrishnan, Geetha, E-mail: kbmaiti@tifr.res.in [Department of Physics, University of Warwick, Coventry, CV4 7AL (United Kingdom)
2011-01-01
We studied the electronic structure of rare earth hexaborides, CeB{sub 6}, PrB{sub 6} and NdB{sub 6} using state-of-the-art high resolution photoemission spectroscopy. CeB{sub 6} is a dense Kondo system. PrB{sub 6} and NdB{sub 6} are antiferromagnetic (Neel temperature {approx}7 K), known to be stable moment systems and do not exhibit Kondo effect. Photoemission spectra exhibit distinct signature of surface and bulk electronic structures of these compounds. The energy position of the surface feature is not influenced by the 4f density of states. High resolution spectra of CeB{sub 6} reveal multiple Kondo resonance features in the bulk spectra due to various photoemission final states. Interestingly, high resolution photoemission spectra of antiferromagnetic PrB{sub 6} also exhibit a sharp feature at the Fermi level that shows temperature dependence similar to the Kondo resonance features.
Validity of equation-of-motion approach to kondo problem in the large N limit
Energy Technology Data Exchange (ETDEWEB)
Zhu, Jian-xin [Los Alamos National Laboratory; Ting, C S [UNIV OF HOUSTON; Qi, Yunong [UNIV OF HOUSTON
2008-01-01
The Anderson impurity model for Kondo problem is investigated for arbitrary orbit-spin degeneracy N of the magnetic impurity by the equation of motion method (EOM). By employing a new decoupling scheme, a self-consistent equation for the one-particle Green function is derived and numerically solved in the large-N approximation. For the particle-hole symmetric Anderson model with finite Coulomb interaction U, we show that the Kondo resonance at the impurity site exists for all N {>=} 2. The approach removes the pathology in the standard EOM for N = 2, and has the same level of applicability as non-crossing approximation. For N = 2, an exchange field splits the Kondo resonance into only two peaks, consist with the result from more rigorous numerical renormalization group (NRG) method. The temperature dependence of the Kondo resonance peak is also discussed.
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.
Blocking transport resonances via Kondo many-body entanglement in quantum dots
Niklas, Michael; Smirnov, Sergey; Mantelli, Davide; Margańska, Magdalena; Nguyen, Ngoc-Viet; Wernsdorfer, Wolfgang; Cleuziou, Jean-Pierre; Grifoni, Milena
2016-08-01
Many-body entanglement is at the heart of the Kondo effect, which has its hallmark in quantum dots as a zero-bias conductance peak at low temperatures. It signals the emergence of a conducting singlet state formed by a localized dot degree of freedom and conduction electrons. Carbon nanotubes offer the possibility to study the emergence of the Kondo entanglement by tuning many-body correlations with a gate voltage. Here we show another side of Kondo correlations, which counterintuitively tend to block conduction channels: inelastic co-tunnelling lines in the magnetospectrum of a carbon nanotube strikingly disappear when tuning the gate voltage. Considering the global SU(2) \\xotime SU(2) symmetry of a nanotube coupled to leads, we find that only resonances involving flips of the Kramers pseudospins, associated to this symmetry, are observed at temperatures and voltages below the corresponding Kondo scale. Our results demonstrate the robust formation of entangled many-body states with no net pseudospin.
Kondo effect in triple quantum dots: interplay between continuous and discrete symmetries
Energy Technology Data Exchange (ETDEWEB)
Kikoin, K. [Department of Physics, Ben-Gurion University, Beer-Sheva, 84105 (Israel)]. E-mail: kikoin@bgumail.bgu.ac.il; Kuzmenko, T. [Department of Physics, Ben-Gurion University, Beer-Sheva, 84105 (Israel); Avishai, Y. [Department of Physics, Ben-Gurion University, Beer-Sheva, 84105 (Israel); Ilse Kats Center for Nano-Technology, Ben-Gurion University, Beer-Sheva, 84105 (Israel)
2006-05-01
The physics of Kondo effect and related phenomena in a triangular triple quantum dot (TTQD) is studied. A fascinating property of TTQD is the interplay between continuous SU(2) symmetry in spin space and discrete C{sub 3v} symmetry in real space. We show that this interplay is manifested in strong oscillations of conductance as a function of magnetic flux through TTQD due to interplay between Kondo and Aharonov-Bohm effect.
Photoemission in YbCu sub 2 Si sub 2 : Problems with the Kondo impurity model
Energy Technology Data Exchange (ETDEWEB)
Lawrence, J.M. (California Univ., Irvine (United States)); Arko, A.J.; Joyce, J.J.; Canfield, P.C.; Fisk, Z.; Thompson, J.D. (Los Alamos National Lab., NM (United States))
1991-01-01
We report valence band photoemission results for YbCu{sub 2}Si{sub 2}. The 4f{sup 13}(J=7/2) final state peak, centered 60meV below the Fermi level {epsilon}{sub F}, lacks the temperature dependence and is broader than predicted for a Kondo resonance. Together with the recent photoemission results for cerium compounds, these results raise serious doubts about the Kondo impurity explanation of heavy fermion photoemission. 7 refs., 3 figs.
Photoemission in YbCu sub 2 Si sub 2 : problem with the Kondo impurity model
Energy Technology Data Exchange (ETDEWEB)
Lawrence, J.M.; Arko, A.J.; Joyce, J.J.; Canfield, P.C.; Fisk, Z.; Thompson, J.D.; Bartlett, R.J. (Los Alamos National Lab., NM (United States))
1992-02-01
We report valence band photoemission results for YbCu{sub 2}Si{sub 2}. The 4f{sup 13}(J = 7/2) final state peak, centered 60 meV below the Fermi level element of{sub F}, lacks the temperature dependence and is broader than predicted for a Kondo resonance. Together with recent photoemission results for cerium compounds, these results raise serious doubts about the Kondo impurity explanation of heavy fermion photoemission. (orig.).
Donnellan, Thomas; Maxwell, E A; Plumpton, C
1968-01-01
Lattice Theory presents an elementary account of a significant branch of contemporary mathematics concerning lattice theory. This book discusses the unusual features, which include the presentation and exploitation of partitions of a finite set. Organized into six chapters, this book begins with an overview of the concept of several topics, including sets in general, the relations and operations, the relation of equivalence, and the relation of congruence. This text then defines the relation of partial order and then partially ordered sets, including chains. Other chapters examine the properti
Controlling orbital-selective Kondo effects in a single molecule through coordination chemistry
Energy Technology Data Exchange (ETDEWEB)
Tsukahara, Noriyuki; Kawai, Maki; Takagi, Noriaki, E-mail: n-takagi@k.u-tokyo.ac.jp [Department of Advanced Materials Science, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Minamitani, Emi; Kim, Yousoo [RIKEN, 2-1 Hirosawa, Saitama 351-0198 (Japan)
2014-08-07
Iron(II) phthalocyanine (FePc) molecule causes novel Kondo effects derived from the unique electronic structure of multi-spins and multi-orbitals when attached to Au(111). Two unpaired electrons in the d{sub z}{sup 2} and the degenerate dπ orbitals are screened stepwise, resulting in spin and spin+orbital Kondo effects, respectively. We investigated the impact on the Kondo effects of the coordination of CO and NO molecules to the Fe{sup 2+} ion as chemical stimuli by using scanning tunneling microscopy (STM) and density functional theory calculations. The impacts of the two diatomic molecules are different from each other as a result of the different electronic configurations. The coordination of CO converts the spin state from triplet to singlet, and then the Kondo effects completely disappear. In contrast, an unpaired electron survives in the molecular orbital composed of Fe d{sub z}{sup 2} and NO 5σ and 2π* orbitals for the coordination of NO, causing a sharp Kondo resonance. The isotropic magnetic response of the peak indicates the origin is the spin Kondo effect. The diatomic molecules attached to the Fe{sup 2+} ion were easily detached by applying a pulsed voltage at the STM junction. These results demonstrate that the single molecule chemistry enables us to switch and control the spin and the many-body quantum states reversibly.
Enhanced Kondo Effect in an Electron System Dynamically Coupled with Local Optical Phonon
Hotta, Takashi
2007-08-01
We discuss Kondo behavior of a conduction electron system coupled with local optical phonon by analyzing the Anderson-Holstein model with the use of a numerical renormalization group (NRG) method. There appear three typical regions due to the balance between Coulomb interaction Uee and phonon-mediated attraction Uph. For Uee>Uph, we observe the standard Kondo effect concerning spin degree of freedom. Since the Coulomb interaction is effectively reduced as Uee-Uph, the Kondo temperature TK is increased when Uph is increased. On the other hand, for UeeUph, there occurs the Kondo effect concerning charge degree of freedom, since vacant and double occupied states play roles of pseudo-spins. Note that in this case, TK is decreased with the increase of Uph. Namely, TK should be maximized for Uee≈ Uph. Then, we analyze in detail the Kondo behavior at Uee=Uph, which is found to be explained by the polaron Anderson model with reduced hybridization of polaron and residual repulsive interaction among polarons. By comparing the NRG results of the polaron Anderson model with those of the original Anderson-Holstein model, we clarify the Kondo behavior in the competing region of Uee≈ Uph.
Kondo effect and spin quenching in high-spin molecules on metal substrates
Jacob, D.; Soriano, M.; Palacios, J. J.
2013-10-01
Using a state-of-the art combination of density functional theory and impurity solver techniques, we present a complete and parameter-free picture of the Kondo effect in the high-spin (S=3/2) coordination complex known as manganese phthalocyanine adsorbed on the Pb(111) surface. We calculate the correlated electronic structure and corresponding tunnel spectrum and find an asymmetric Kondo resonance, as recently observed in experiments. Contrary to previous claims, the Kondo resonance stems from only one of three possible Kondo channels with origin in the Mn 3d orbitals, its peculiar asymmetric shape arising from the modulation of the hybridization due to a strong coupling to the organic ligand. The spectral signature of the second Kondo channel is strongly suppressed as the screening occurs via the formation of a many-body singlet with the organic part of the molecule. Finally, a spin-1/2 in the 3d shell remains completely unscreened due to the lack of hybridization of the corresponding orbital with the substrate, hence leading to a spin-3/2 underscreened Kondo effect.
Kondo Breakdown and Quantum Oscillations in SmB_{6}.
Erten, Onur; Ghaemi, Pouyan; Coleman, Piers
2016-01-29
Recent quantum oscillation experiments on SmB_{6} pose a paradox, for while the angular dependence of the oscillation frequencies suggest a 3D bulk Fermi surface, SmB_{6} remains robustly insulating to very high magnetic fields. Moreover, a sudden low temperature upturn in the amplitude of the oscillations raises the possibility of quantum criticality. Here we discuss recently proposed mechanisms for this effect, contrasting bulk and surface scenarios. We argue that topological surface states permit us to reconcile the various data with bulk transport and spectroscopy measurements, interpreting the low temperature upturn in the quantum oscillation amplitudes as a result of surface Kondo breakdown and the high frequency oscillations as large topologically protected orbits around the X point. We discuss various predictions that can be used to test this theory.
Fractionalized Fermi liquid in a Kondo-Heisenberg model
Tsvelik, A. M.
2016-10-01
The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. In agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003), 10.1103/PhysRevLett.90.216403], the resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations. The system undergoes a phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.
SU(4) Kondo entanglement in double quantum dot devices
Bonazzola, Rodrigo; Andrade, J. A.; Facio, Jorge I.; García, D. J.; Cornaglia, Pablo S.
2017-08-01
We analyze, from a quantum information theory perspective, the possibility of realizing an SU(4) entangled Kondo regime in semiconductor double quantum dot devices. We focus our analysis on the ground-state properties and consider the general experimental situation where the coupling parameters of the two quantum dots differ. We model each quantum dot with an Anderson-type Hamiltonian including an interdot Coulomb repulsion and tunnel couplings for each quantum dot to independent fermionic baths. We find that the spin and pseudospin entanglements can be made equal, and the SU(4) symmetry recovered, if the gate voltages are chosen in such a way that the average charge occupancies of the two quantum dots are equal, and the double occupancy on the double quantum dot is suppressed. We present density matrix renormalization group numerical results for the spin and pseudospin entanglement entropies, and analytical results for a simplified model that captures the main physics of the problem.
Mott-Kondo insulator behavior in the iron oxychalcogenides
Freelon, B.; Liu, Yu Hao; Chen, Jeng-Lung; Craco, L.; Laad, M. S.; Leoni, S.; Chen, Jiaqi; Tao, Li; Wang, Hangdong; Flauca, R.; Yamani, Z.; Fang, Minghu; Chang, Chinglin; Guo, J.-H.; Hussain, Z.
2015-10-01
We perform a combined experimental-theoretical study of the Fe-oxychalcogenides (FeO C h ) series La2O2Fe2O M2 (M =S , Se), which are among the latest Fe-based materials with the potential to show unconventional high-Tc superconductivity (HTSC). A combination of incoherent Hubbard features in x-ray absorption and resonant inelastic x-ray scattering spectra, as well as resistivity data, reveal that the parent FeO C h are correlation-driven insulators. To uncover microscopics underlying these findings, we perform local density approximation-plus-dynamical mean field theory (LDA+DMFT) calculations that reveal a novel Mott-Kondo insulating state. Based upon good agreement between theory and a range of data, we propose that FeO C h may constitute an ideal testing ground to explore HTSC arising from a strange metal proximate to a novel selective-Mott quantum criticality.
Frequency Domain Errors in Variables Approach for Two Channel SIMO System Identification
2009-06-24
Signal et Image, ENSEIRB/UMR CNRS 5218 IMS Dpt. LAPS, Université Bordeaux 1, France william.bobillet@etu.u-bordeaux1.fr Dipartimento di Fisica e...without loss of generality . - - - ? h1(k) y1(k) b1(k), (σ21 ) x1(k) - - - ? h2(k) y2(k) b2(k), (σ22 ) x2(k) s(k) Figure 1: two-channel...developed in the fields of statistics and identification, assume that the available data are disturbed by additive error terms. Given a generic process
Nunes, A.; Zanetti, F. M.; Lyra, M. L.
2016-10-01
In this work, we study the transmission characteristics of a two-channels coupler model system using the Boundary Wall Method (BWM) to determine the solution of the corresponding scattering problem of an incident plane wave. We show that the BWM provides detailed information regarding the transmission resonances. In particular, we focus on the case of single channel input aiming to explore the energy switching performance of the coupler. We show that the coupler geometry can be tailored to allow for the first transmission resonances to be predominantly transmitted on specific output channels, an important characteristic for the realization of logical operations.
Majorana bound states in two-channel time-reversal-symmetric nanowire systems.
Gaidamauskas, Erikas; Paaske, Jens; Flensberg, Karsten
2014-03-28
We consider time-reversal-symmetric two-channel semiconducting quantum wires proximity coupled to a conventional s-wave superconductor. We analyze the requirements for a nontrivial topological phase and find that the necessary conditions are (1) the determinant of the pairing matrix in channel space must be negative, (2) inversion symmetry must be broken, and (3) the two channels must have different spin-orbit couplings. The first condition can be implemented in semiconducting nanowire systems where interactions suppress intra-channel pairing, while the inversion symmetry can be broken by tuning the chemical potentials of the channels. For the case of collinear spin-orbit directions, we find a general expression for the topological invariant by block diagonalization into two blocks with chiral symmetry only. By projection to the low-energy sector, we solve for the zero modes explicitly and study the details of the gap closing, which in the general case happens at finite momenta.
Implementation of a Two-Channel Maximally Decimated Filter Bank using Switched Capacitor Circuits
Directory of Open Access Journals (Sweden)
J. Nahlik
2013-04-01
Full Text Available The aim of this paper is to describe the implementation of a two-channel filter bank (FB using the switched capacitor (SC technique considering real properties of operational amplifiers (OpAmps. The design procedure is presented and key recommendations for the implementation are given. The implementation procedure describes the design of two-channel filter bank using an IIR Cauer filter, conversion of IIR into the SC filters and the final implementation of the SC filters. The whole design and an SC circuit implementation is performed by a PraCAn package in Maple. To verify the whole filter bank, resulting real property circuit structures are completely simulated by WinSpice and ELDO simulators. The results confirm that perfect reconstruction conditions can be almost accepted for the filter bank implemented by the SC circuits. The phase response of the SC filter bank is not strictly linear due to the IIR filters. However, the final ripple of a magnitude frequency response in the passband is almost constant, app. 0.5 dB for a real circuit analysis.
Alternating-Current Conductivity for a Two-Channel Interacting Quantum Wire
Institute of Scientific and Technical Information of China (English)
PENG De-Jun; CHENG Fang; ZHOU Guang-Hui
2007-01-01
We investigate theoretically the ac conductivity of a clean two-channel spinless quantum wire in the presence of both short-ranged intra- and inter-channel electron-electron interactions. In the Luttinger-liquid regime, we formulize the action functional of the system with an external time-varying electric field. The obtained expression of ac conductivity for the system within linear response theory is generally an oscillation function of the interaction strength, the driving frequency as well as the measured position in the wire. The numerical examples demonstrate that the amplitude of ac conductivity is renormalized by the both interactions, and the dc conductivity of the system with inter-channel interaction is smaller than that without inter-channel interaction.
Study of ultra-wideband radar signals-generated technology using two-channel signal generator
Institute of Scientific and Technical Information of China (English)
Wan Yonglun; Lu Youxin; Si Qiang; Wang Xuegang; Cao Guangping
2007-01-01
Synthesis of ultra-wideband (UWB) linear frequency modulation radar signals is a very important technology for microwave imaging, target identification and detection of low radar-cross-section (RCS) targets. A new method of UWB radar signals generation with two-channel signal generator is presented. The realization structure is given; the principle and errors of signal synthesis are analyzed. At the same time, an automatic adjustment measure of signal phase is proposed because of phase discontinuity of waveform in this method. The simulation experiment and analysis results indicate that radar signals with large instantaneous bandwidth can be generated by means of this method on the condition that the high-speed digital devices are limited.
Polyphase Structure Based Eigen Design of Two-Channel Quadrature Mirror Filter Bank
Directory of Open Access Journals (Sweden)
S. K. Agrawal
2014-09-01
Full Text Available This paper presents a method for the design of two-channel quadrature mirror filter (QMF banks with linear phase in frequency domain. Low-pass prototype filter of the QMF bank is implemented using polyphase decomposition. Prototype filter coefficients are optimized to minimize an objective function using eigenvalue-eigenvector approach without matrix inversion. The objective function is formulated as a weighted sum of four terms, pass-band error and stop-band residual energy of low-pass analysis filter, the square error of the overall transfer function at the quadrature frequency and amplitude distortion of the filter bank. The simulation results clearly show that the proposed method requires less computational efforts in comparison to the other state-of-art existing design methods.
CGC/saturation approach for soft interactions at high energy: a two channel model
Energy Technology Data Exchange (ETDEWEB)
Gotsman, E.; Maor, U. [Tel Aviv University, Department of Particle Physics, School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Science, Tel Aviv (Israel); Levin, E. [Tel Aviv University, Department of Particle Physics, School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Science, Tel Aviv (Israel); Universidad Tecnica Federico Santa Maria, Departemento de Fisica, Centro Cientifico-Tecnologico de Valparaiso, Valparaiso (Chile)
2015-05-15
In this paper we continue the development of a model for strong interactions at high energy, based on two ingredients: the CGC/saturation approach and the BFKL Pomeron. In our approach, the unknown mechanism of confinement of quarks and gluons is characterized by several numerical parameters, which are extracted from the experimental data. We demonstrate that the two channel model successfully describes the experimental data, including both the value of the elastic slope and the energy behavior of the single diffraction cross section. We show that the disagreement with the experimental data of our previous single channel eikonal model (Gotsman et al., Eur Phys J C 75:1-18, 2015) stems from the simplified approach used for the hadron structure and is not related to our principal theoretical input, based on the CGC/saturation approach. (orig.)
Dhiman, Isha
2015-01-01
This work is devoted to the development of a novel theoretical approach, named hybrid approach, to handle a localized bottleneck in a symmetrically coupled two-channel totally asymmetric simple exclusion process with Langmuir kinetics. The hybrid approach is combined with singular perturbation technique to get steady-state phase diagrams and density profiles. We have thoroughly examined the role played by the strength of bottleneck, binding constant and lane-changing rate in the system dynamics. The appearances of bottleneck-induced shock, a bottleneck phase and Meissner phase are explained. Further, the critical values of bottleneck rate are identified, which signify the changes in the topology of phase diagram. It is also found that increase in lane-changing rate as well as unequal attachment, detachment rates weaken the bottleneck effect. Our theoretical arguments are in good agreement with extensively performed Monte Carlo simulations.
CGC/saturation approach for soft interactions at high energy: a two channel model
Gotsman, E; Maor, U
2015-01-01
In this paper we continue the development of a model for strong interactions at high energy, based on two ingredients: CGC/saturation approach and the BFKL Pomeron. In our approach, the unknown mechanism of confinement of quarks and gluons, is characterized by several numerical parameters, which are extracted from the experimental data. We demonstrate that the two channel model, successfully describes the experimental data, including both the value of the elastic slope and the energy behavior of the single diffraction cross section. We show that the disagreement with experimental data of our previous single channel eikonal model [6] stems from the simplified approach used for the hadron structure, and is not related to our principal theoretical input, based on the CGC/saturation approach.
Charge Kondo effect in negative-U quantum dots with superconducting electrodes
Fang, Tie-Feng; Guo, Ai-Min; Lu, Han-Tao; Luo, Hong-Gang; Sun, Qing-Feng
2017-08-01
Recent experimental realization of superconducting quantum dot devices with intradot attraction U [Nature (London) 521, 196 (2015), 10.1038/nature14398; Phys. Rev. X 6, 041042 (2016), 10.1103/PhysRevX.6.041042] offers unique opportunities to study the charge Kondo effect in a superconducting environment. In such devices pseudospin flips are caused by two tunneling processes. One is the cotunneling of normal electrons which generates near-gap Kondo resonances in the single-electron spectral density. This negative-U charge Kondo effect is more robust than the conventional spin Kondo effect against the suppression by the superconductivity. The other tunneling is the mean-field Cooper-pair tunneling which produces a zero-energy bound state in the pair spectral density. Interesting crossover physics from the strongly-correlated Kondo screening to the mean-field polarization of local pseudospin is demonstrated. Due to the interplay of these two tunnelings, the supercurrent is suppressed for intermediate couplings, but it can increase to the unitary limits both in the strong and weak coupling regimes. We obtain the magnetic field-dependent supercurrent which is consistent with the key experimental findings.
Effect of Spin-Orbit Coupling on Kondo Phenomena in f7-Electron Systems
Hotta, Takashi
2015-11-01
In order to promote our basic understanding of the Kondo behavior recently observed in europium compounds, we analyze an impurity Anderson model with seven f electrons at an impurity site by employing a numerical renormalization group method. The local part of the model consists of Coulomb interactions among f electrons, spin-orbit coupling λ, and crystalline electric field (CEF) potentials, while we consider the hybridization V between local f electrons and single-band conduction electrons with au symmetry. For λ = 0, we observe underscreening Kondo behavior for appropriate values of V, characterized by an entropy change from ln 8 to ln 7, in which one of the seven f electrons is screened by conduction electrons. When λ is increased, we obtain two types of behavior depending on the value of V. For large V, we find an entropy release of ln 7 at low temperatures, determined by the level splitting energy due to the hybridization. For small V, we also observe an entropy change from ln 8 to ln 2 by the level splitting due to the hybridization, but at low temperatures, ln 2 entropy is found to be released, leading to the Kondo effect. We emphasize that the Kondo behavior for small V is observed for realistic values of λ on the order of 0.1 eV. We also discuss the effect of CEF potentials and the multipole properties in the Kondo behavior reported in this paper.
Transport signatures of Kondo physics and quantum criticality in graphene with magnetic impurities
Ruiz-Tijerina, David A.; Dias da Silva, Luis G. G. V.
2017-03-01
Localized magnetic moments have been predicted to develop in graphene samples with vacancies or adsorbates. The interplay between such magnetic impurities and graphene's Dirac quasiparticles leads to remarkable many-body phenomena, which have, so far, proved elusive to experimental efforts. In this article we study the thermodynamic, spectral, and transport signatures of quantum criticality and Kondo physics of a dilute ensemble of atomic impurities in graphene. We consider vacancies and adatoms that either break or preserve graphene's C3 v and inversion symmetries. In a neutral graphene sample, all cases display symmetry-dependent quantum criticality, leading to enhanced impurity scattering for asymmetric impurities, in a manner analogous to bound-state formation by nonmagnetic resonant scatterers. Kondo correlations emerge only in the presence of a back gate, with estimated Kondo temperatures well within the experimentally accessible domain for all impurity types. For symmetry-breaking impurities at charge neutrality, quantum criticality is signaled by T-2 resistivity scaling, leading to full insulating behavior at low temperatures, while low-temperature resistivity plateaus appear both in the noncritical and Kondo regimes. By contrast, the resistivity contribution from symmetric vacancies and hollow-site adsorbates vanishes at charge neutrality and for arbitrary back-gate voltages, respectively. This implies that local probing methods are required for the detection of both Kondo and quantum critical signatures in these symmetry-preserving cases.
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.
Theory of Fano-Kondo effect in quantum dot systems: Temperature dependence of the Fano line shapes
Energy Technology Data Exchange (ETDEWEB)
Maruyama, I. [Physikalisches Institut der Universitaet Bonn, Nussallee 12, 53115 Bonn (Germany)]. E-mail: maru@th.physik.uni-bonn.de; Shibata, N. [Department of Basic Science, University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902 (Japan); Ueda, K. [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa, Chiba 277-8581 (Japan)
2006-05-01
The Fano-Kondo effect in zero-bias conductance is studied based on a theoretical model for the T-shaped quantum dot by the finite temperature density matrix renormalization group method. The modification of the two Fano line shapes at much higher temperatures than the Kondo temperature is also investigated by the effective Fano parameter estimated as a fitting parameter.
Kubo, T.; Tokura, Y.; Tarucha, S.
2010-01-01
We theoretically investigate spin-dependent electron transport through an Aharonov-Bohm-Casher interferometer containing a laterally coupled double quantum dot. In particular, we numerically calculate the Aharonov-Bohm and Aharonov-Casher oscillations of the linear conductance in the Kondo regime. We show that the AC oscillation in the Kondo regime deviates from the sinusoidal form.
Energy Technology Data Exchange (ETDEWEB)
Schaefer, Stefan [DESY (Germany). Neumann Inst. for Computing
2016-11-01
These configurations are currently in use in many on-going projects carried out by researchers throughout Europe. In particular this data will serve as an essential input into the computation of the coupling constant of QCD, where some of the simulations are still on-going. But also projects computing the masses of hadrons and investigating their structure are underway as well as activities in the physics of heavy quarks. As this initial project of gauge field generation has been successful, it is worthwhile to extend the currently available ensembles with further points in parameter space. These will allow to further study and control systematic effects like the ones introduced by the finite volume, the non-physical quark masses and the finite lattice spacing. In particular certain compromises have still been made in the region where pion masses and lattice spacing are both small. This is because physical pion masses require larger lattices to keep the effects of the finite volume under control. At light pion masses, a precise control of the continuum extrapolation is therefore difficult, but certainly a main goal of future simulations. To reach this goal, algorithmic developments as well as faster hardware will be needed.
Finite-size effect and Kondo screening effect in an A-B ring with a quantum dot
Institute of Scientific and Technical Information of China (English)
Wu Shao-Quan; Wang Shun-Jin; Sun Wei-Li; Yu Wan-Lun
2004-01-01
The properties of the ground state of a closed dot-ring system with a magnetic flux in the Kondo regime are studied theoretically by means of a one-impurity Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. It is shown that at T=0, a suppressed Kondo effect exists in this system even when the mean level spacing of electrons in the ring is larger than the bulk Kondo temperature. The physical quantities depend sensitively on both the parity of the system and the size of the ring; the rich physical behaviour can be attributed to the coexistence of both the finite-size effect and the Kondo screening effect. It is also possible to detect the Kondo screening cloud by measuring the persistent current or the zero field impurity susceptibility Ximp directly in future experiments.
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)
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 an antiferromagnetic ordered metallic Kondo compound, no such instability is observed in CeNiSn in magnetic fields up to 9 T. Both the sharp magnetic excitations (at 2 and 4 meV) appear significantly broader for energy and momentum transfer at high fields, while the ground-state correlations (probed by chi'(0)) remain...
Quantum phase transitions and thermodynamics of the power-law Kondo model
Mitchell, Andrew K.; Vojta, Matthias; Bulla, Ralf; Fritz, Lars
2013-11-01
We revisit the physics of a Kondo impurity coupled to a fermionic host with a diverging power-law density of states near the Fermi level, ρ(ω)˜|ω|r, with exponent -1
Kondo decoherence : finding the right spin model for iron impurities in gold and silver.
Energy Technology Data Exchange (ETDEWEB)
Costi, T. A.; Bergqvist, L.; Weichselbaum, A.; von Delft, J.; Micklitz, T.; Rosch, A.; Mavropoulos, P.; Dederichs, P. H.; Mallet, F.; Saminadayar, L.; Bauerle, C. (Materials Science Division); (Forschungszentrum Julich); (Ludwig-Maximilians-Univ. Munchen); (Univ. of Cologne); (CNRS); (Univ. Joseph Fourier); (Inst. Univ. de France)
2009-02-01
We exploit the decoherence of electrons due to magnetic impurities, studied via weak localization, to resolve a long-standing question concerning the classic Kondo systems of Fe impurities in the noble metals gold and silver: which Kondo-type model yields a realistic description of the relevant multiple bands, spin, and orbital degrees of freedom? Previous studies suggest a fully screened spin S Kondo model, but the value of S remained ambiguous. We perform density functional theory calculations that suggest S=3/2. We also compare previous and new measurements of both the resistivity and decoherence rate in quasi-one-dimensional wires to numerical renormalization group predictions for S=1/2, 1, and 3/2, finding excellent agreement for S=3/2.
Spin relaxation and the Kondo effect in transition metal dichalcogenide monolayers
Rostami, Habib; Moghaddam, Ali G.; Asgari, Reza
2016-12-01
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.
Quantum dots with even number of electrons: kondo effect in a finite magnetic field
Pustilnik; Avishai; Kikoin
2000-02-21
We show that the Kondo effect can be induced by an external magnetic field in quantum dots with an even number of electrons. If the Zeeman energy B is close to the single-particle level spacing Delta in the dot, the scattering of the conduction electrons from the dot is dominated by an anisotropic exchange interaction. A Kondo resonance then occurs despite the fact that B exceeds by far the Kondo temperature T(K). As a result, at low temperatures T
Oguri, Akira; Amaha, Shinichi; Nisikawa, Yunori; Hewson, A. C.; Tarucha, Seigo; Numata, Takahide
2010-03-01
We study transport through a triangular triple quantum dot (TTQD) connected to two noninteracting leads, using the numerical renormalization group. The system has been theoretically revealed to show a variety of Kondo effects depending on the electron filling of the triangle [1]. For instance, the SU(4) Kondo effect takes place at three-electron filling, and a two-stage Kondo screening of a high-spin S=1 Nagaoka state takes place at four-electron filling. Because of the enhanced freedom in the configurations, however, the large parameter space of the TTQD still has not been fully explored, especially for large deformations. We report the effects of the inhomogeneity in the inter-dot couplings and the level positions in a wide region of the filling. [1] T. Numata, Y. Nisikawa, A. Oguri, and A. C. Hewson: PRB 80, 155330 (2009).
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.
Nonequilibrium Transport through a Kondo-dot in a Magnetic Field
DEFF Research Database (Denmark)
Wölfle, Peter; Rosch, Achim; Paaske, Jens
2002-01-01
Electron transport through a quantum-dot in the Coulomb blockade regime is modeled by a Kondo-type hamiltonian describing spin-dependent tunneling and exchange interaction with the local spin. We consider the regime of large transport voltage V and magnetic field B with max(V, B) » Tk, the Kondo ...... to be generalized to allow for frequency dependent coupling functions. We simplify the full RG equations in the spirit of poor man’s scaling and calculate M and G in leading order of 1/ln[(V, B)/T k]....
Energy Technology Data Exchange (ETDEWEB)
Joyce, J.J.; Arko, A.J.; Lawrence, J.; Canfield, P.C.; Fisk, Z.; Bartlett, R.J.; Thompson, J.D. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States))
1992-01-13
4{ital f} levels in Ce heavy-fermion compounds are examined using resonant photoemission. We find the following inconsistencies with the predictions of the Kondo model: (a) All temperature dependence can be accounted for simply by phonon broadening and the Fermi function; (b) the spectral weights of the features near {ital E}{sub {ital F}} do not scale with {ital T}{sub {ital K}}; and (c) the line shape of the feature previously identified as the Kondo resonance is Lorentzian and about an order of magnitude broader than predictions. Instrument resolution is not a limiting factor.
Nonequilibrium Transport through a Kondo-dot in a Magnetic Field
DEFF Research Database (Denmark)
Wölfle, Peter; Rosch, Achim; Paaske, Jens;
2002-01-01
Electron transport through a quantum-dot in the Coulomb blockade regime is modeled by a Kondo-type hamiltonian describing spin-dependent tunneling and exchange interaction with the local spin. We consider the regime of large transport voltage V and magnetic field B with max(V, B) » Tk, the Kondo...... temperature, and show that a renormalized perturbation theory can be formulated describing the local magnetization M and the differential conductance G quantitatively. Based on the structure of leading logarithmic corrections in bare perturbation theory we argue that the perturbative renormalization group has...
Kondo effect in transport through Aharonov-Bohm and Aharonov-Casher interferometers
Lobos, A. M.; Aligia, A. A.
2009-10-01
We derive the extension of the Hubbard model to include Rashba spin-orbit coupling that correctly describes Aharonov-Bohm and Aharonov-Casher phases in a ring under applied magnetic and electric fields. When the ring is connected to conducting leads, we develop a formalism that is able to describe both, Kondo and interference effects. We find that in the Kondo regime, the spin-orbit coupling reduces strongly the conductance from the unitary limit. This effect in combination with the magnetic flux, can be used to produce spin polarized carriers.
Kondo effect in transport through Aharonov-Bohm and Aharonov-Casher interferometers
Energy Technology Data Exchange (ETDEWEB)
Lobos, A.M. [DPMC-MaNEP, University of Geneva, 24 Quai Ernest Ansermet, CH-1211 Geneva 4 (Switzerland); Aligia, A.A., E-mail: aligia@cab.cnea.gov.a [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica, 8400 Bariloche (Argentina)
2009-10-15
We derive the extension of the Hubbard model to include Rashba spin-orbit coupling that correctly describes Aharonov-Bohm and Aharonov-Casher phases in a ring under applied magnetic and electric fields. When the ring is connected to conducting leads, we develop a formalism that is able to describe both, Kondo and interference effects. We find that in the Kondo regime, the spin-orbit coupling reduces strongly the conductance from the unitary limit. This effect in combination with the magnetic flux, can be used to produce spin polarized carriers.
A Theoretic Approach to SU(4) Kondo Effect in Carbon Nanotube Quantum Dots
Institute of Scientific and Technical Information of China (English)
ZHU Rui
2006-01-01
We propose a mean Geld approach to the transport properties of carbon nanotube quantum dots. Quantum interaction between spin and orbital pseudo-spin degrees of freedom results in an SU(4) Kondo effect at low temperatures. By calculating the chemical potentials and the tunnelling strengths, and hence the spectral functions for different coupling constants and applied magnetic fields, we find that this exotic Kondo effect manifests as a four-peak splitting in the non-linear conductance when an axial magnetic field is applied.
Garnica, Manuela; Calleja, Fabián; Vázquez de Parga, Amadeo L.; Miranda, Rodolfo
2014-12-01
Electron acceptor molecules adsorbed on nanostructured graphene grown on Ru(0001) were investigated by low temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS). Our experiments reveal a considerable charge transfer from the substrate to the single molecules leading to the partial occupation of the LUMO of the neutral molecules. The nanostructured graphene modulates the hybridization between the transferred unpaired electron and the ruthenium conduction electrons leading to the appearance of a Kondo effect. Spatially resolved LT-STS allows the high resolution mapping of the spin distribution of the charge transferred and a characteristic inelastic Kondo features associated to specific vibrational modes.
Dual Lattice of ℤ-module Lattice
Directory of Open Access Journals (Sweden)
Futa Yuichi
2017-07-01
Full Text Available In this article, we formalize in Mizar [5] the definition of dual lattice and their properties. We formally prove that a set of all dual vectors in a rational lattice has the construction of a lattice. We show that a dual basis can be calculated by elements of an inverse of the Gram Matrix. We also formalize a summation of inner products and their properties. Lattice of ℤ-module is necessary for lattice problems, LLL(Lenstra, Lenstra and Lovász base reduction algorithm and cryptographic systems with lattice [20], [10] and [19].
Multi-spectral image fusion method based on two channels non-separable wavelets
Institute of Scientific and Technical Information of China (English)
LIU Bin; PENG JiaXiong
2008-01-01
A construction method of two channels non-separable wavelets filter bank which dilation matrix is [1, 1; 1, -1] and its application in the fusion of multi-spectral image are presented. Many 4x4 filter banks are designed. The multi-spectral image fusion algorithm based on this kind of wavelet is proposed. Using this filter bank, multi-resolution wavelet decomposition of the intensity of multi-spectral image and panchromatic image is performed, and the two low-frequency components of the intensity and the panchromatic image are merged by using a tradeoff parameter. The experiment results show that this method is good in the preservation of spectral quality and high spatial resolution information. Its performance in preserving spectral quality and high spatial information is better than the fusion method based on DWFT and IHS. When the parameter t is closed to 1, the fused image can obtain rich spectral information from the original MS image. The amount of computation reduced to only half of the fusion method based on four channels wavelet transform.
Applying two channels to vector space secret sharing based multi-signature scheme
Institute of Scientific and Technical Information of China (English)
XIAO Qing-hua; PING Ling-di; CHEN Xiao-ping; PAN Xue-zeng
2005-01-01
Secret sharing and digital signature is an important research area in information security and has wide applications in such fields as safeguarding and legal use of confidential information, secure multiparty computation and electronic commerce. But up to now, study of signature based on general vector space secret sharing is very weak. Aiming at this drawback, the authors did some research on vector space secret sharing against cheaters, and proposed an efficient but secure vector space secret sharing based multi-signature scheme, which is implemented in two channels. In this scheme, the group signature can be easily produced if an authorized subset of participants pool their secret shadows and it is impossible for them to generate a group signature if an unauthorized subset of participants pool their secret shadows. The validity of the group signature can be verified by means of verification equations. A group signature of authorized subset of participants cannot be impersonated by any other set of participants. Moreover, the suspected forgery can be traced, and the malicious participants can be detected in the scheme. None of several possible attacks can successfully break this scheme.
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.
Detection of Ground Moving Targets for Two-Channel Spaceborne SAR-ATI
Directory of Open Access Journals (Sweden)
Diannong Liang
2010-01-01
Full Text Available Many present spaceborne synthetic aperture radar (SAR systems are constrained to only two channels for ground moving target indication (GMTI. Along-track interferometry (ATI technique is currently exploited to detect slowly moving targets and measure their radial velocity and azimuth real position. In this paper, based on the joint probability density function (PDF of interferogram's phase and amplitude and the two hypotheses “clutter” and “clutter plus signal”, several constant false alarm rate (CFAR detection criteria are analyzed for their capabilities and limitations under low signal-to-clutter ratio (SCR and low clutter-to-noise ratio (CNR conditions. The CFAR detectors include one-step CFAR detector with interferometric phase, two-step CFAR detectors, and two-dimensional (2D CFAR detector. The likelihood ratio test (LRT based on the Neyman-Pearson (NP criterion is exploited as an upper bound for the performance of the other CFAR detectors. Performance analyses demonstrate the superiority of the 2D CFAR techniques to detect dim slowly moving targets for spaceborne 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.
Electronic structure and magnetism in the layered triangular lattice compound CeAuAl4Ge2
Zhang, S.; Aryal, N.; Huang, K.; Chen, K.-W.; Lai, Y.; Graf, D.; Besara, T.; Siegrist, T.; Manousakis, E.; Baumbach, R. E.
2017-09-01
Results are reported for the f -electron intermetallic CeAuAl4Ge2 , where the atomic arrangement of the cerium ions creates the conditions for possible geometric frustration. The magnetic susceptibility follows a Curie-Weiss temperature dependence at elevated temperatures, revealing that the cerium ions are trivalent. At lower temperatures the crystal electric field splits the Hund's rule multiplet, resulting in a weak low-temperature magnetic exchange interaction and ordering near TM≈1.4 K . This occurs within a metallic Kondo lattice, where electrical resistivity and heat capacity measurements show that the Kondo-driven electronic correlations are negligible. Quantum oscillations are detected in ac-magnetic susceptibility measurements and uncover small charge carrier effective masses. Electronic structure calculations reveal that inclusion of an on-f -site Coulomb repulsion (Hubbard) U results in antiferromagnetic order and causes the f -electron bands to move away from the Fermi level, resulting in electronic behavior that is dominated by the s ,p , and d bands, which are all characterized by light electron masses. Thus, CeAuAl4Ge2 may provide a starting point for investigating geometric magnetic frustration in a cerium lattice without strong Kondo hybridization, where calculations provide useful guidance.
Magalhaes, S. G.; Zimmer, F. M.; Coqblin, B.
2012-12-01
We study here the influence of a random applied magnetic field on the competition between the Kondo effect, the spin glass phase and a ferromagnetic order in disordered cerium systems such as CeNi1-xCux. The model used here takes an intrasite Kondo coupling and an intersite random coupling; both the intersite random coupling and the random magnetic field are described within the Sherrington-Kirkpatrick model and the one-step replica symmetry breaking procedure is also used here. We present phase diagrams giving Temperature versus the Kondo exchange parameter and the random magnetic field makes decrease particularly the importance of the spin glass and ferromagnetic phases.
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...
Environment-modulated Kondo phenomena in FePc/Au(111) adsorption systems
Wang, Yu; Zheng, Xiao; Yang, Jinlong
2016-03-01
Recent scanning tunneling microscopy experiments on electron transport through iron(II) phthalocyanine (FePc) molecules adsorbed on the Au(111) surface have revealed that the measured Kondo conductance signature depends strongly on the specific adsorption site. To understand the physical origin of experimental observations, particularly the variation of Kondo features with the molecular adsorption site, we employ a combined density functional theory (DFT) and hierarchical equations of motion (HEOM) approach to investigate the electronic structure and Kondo correlation in FePc/Au(111) composite systems. The calculation results indicate that, for the on-top adsorption configuration, the two degenerate spin-unpaired dπ orbitals on the Fe center are coupled indirectly through substrate band states, leading to the Fano-like antiresonance line shape in the d I /d V spectra, while for the bridge adsorption configuration, the environment-induced couplings are largely suppressed because of the two different spin-unpaired d orbitals. Therefore, our work suggests that the environment-induced coupling as an essential physical factor could greatly influence the Fano-Kondo features in magnetic molecule/metal composites, and the crucial role of local orbital degeneracy and symmetry is discovered. These findings provide important insights into the electron correlation effects in complex solid-state systems. The usefulness and practicality of the combined DFT+HEOM method is also highlighted.
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.
Strong spin Seebeck effect in Kondo T-shaped double quantum dots
Wójcik, K. P.; Weymann, I.
2017-02-01
We investigate, taking a theoretical approach, the thermoelectric and spin thermoelectric properties of a T-shaped double quantum dot strongly coupled to two ferromagnetic leads, focusing on the transport regime in which the system exhibits the two-stage Kondo effect. We study the dependence of the (spin) Seebeck coefficient, the corresponding power factor and the figure of merit on temperature, leads’ spin polarization and dot level position. We show that the thermal conductance fulfills a modified Wiedemann-Franz law, also in the regime of suppression of subsequent stages of the Kondo effect by the exchange field resulting from the presence of ferromagnets. Moreover, we demonstrate that the spin thermopower is enhanced at temperatures corresponding to the second stage of Kondo screening. Very interestingly, the spin-thermoelectric response of the system is found to be highly sensitive to the spin polarization of the leads. In some cases spin polarization of the order of 1% is sufficient for a strong spin Seebeck effect to occur. This is explained as a consequence of the interplay between the two-stage Kondo effect and the exchange field induced in the double quantum dot. Due to the possibility of tuning the exchange field by the choice of gate voltage, the spin thermopower may also be tuned to be maximal for desired spin polarization of the leads. All calculations are performed with the aid of the numerical renormalization group technique.
Kondo quantum dot coupled to ferromagnetic leads: Numerical renormalization group study
Sindel, M.; Borda, L.; Martinek, J.; Bulla, R.; König, J.; Schön, G.; Maekawa, S.; von Delft, J.
2007-07-01
We systematically study the influence of ferromagnetic leads on the Kondo resonance in a quantum dot tuned to the local moment regime. We employ Wilson’s numerical renormalization group method, extended to handle leads with a spin asymmetric density of states, to identify the effects of (i) a finite spin polarization in the leads (at the Fermi surface), (ii) a Stoner splitting in the bands (governed by the band edges), and (iii) an arbitrary shape of the lead density of states. For a generic lead density of states, the quantum dot favors being occupied by a particular spin species due to exchange interaction with ferromagnetic leads, leading to suppression and splitting of the Kondo resonance. The application of a magnetic field can compensate this asymmetry, restoring the Kondo effect. We study both the gate voltage dependence (for a fixed band structure in the leads) and the spin polarization dependence (for fixed gate voltage) of this compensation field for various types of bands. Interestingly, we find that the full recovery of the Kondo resonance of a quantum dot in the presence of leads with an energy-dependent density of states is possible not only by an appropriately tuned external magnetic field but also via an appropriately tuned gate voltage. For flat bands, simple formulas for the splitting of the local level as a function of the spin polarization and gate voltage are given.
Kondo effect and impurity band conduction in Co:TiO2 magnetic semiconductor
Ramaneti, R.; Lodder, J.C.; Jansen, R.
2007-01-01
The nature of charge carriers and their interaction with local magnetic moments in an oxide magnetic semiconductor is established. For cobalt-doped anatase TiO2 films, we demonstrate conduction in a metallic donor-impurity band. Moreover, we observe a clear signature of the Kondo effect in electrica
The exact decomposition of gauge variables in lattice Yang-Mills theory
Shibata, Akihiro; Kondo, Kei-Ichi; Shinohara, Toru
2010-07-01
In this Letter, we consider lattice versions of the decomposition of the Yang-Mills field a la Cho-Faddeev-Niemi, which was extended by Kondo, Shinohara and Murakami in the continuum formulation. For the SU (N) gauge group, we propose a set of defining equations for specifying the decomposition of the gauge link variable and solve them exactly without using the ansatz adopted in the previous studies for SU (2) and SU (3). As a result, we obtain the general form of the decomposition for SU (N) gauge link variables and confirm the previous results obtained for SU (2) and SU (3).
van Rooij, Linda G. M.; de Vries, Linda S.; van Huffelen, Alexander C.; Toet, Mona C.
2010-01-01
Background Amplitude integrated electroencephalography (aEEG) is a valuable tool for evaluating neonatal encephalopathy and identifying electrographic seizures. Objective To compare seizure activity and background pattern (BGP) between one-channel and two-channel aEEG recordings in full-term neonate
Neveling, K.; Thung, G.W.D.T.; Beulen, L.; Rens-Buijsman, W. van; Gomes, I.; Heuvel, S. van den; Mieloo, H.; Derks-Prinsen, I.; Kater-Baats, E.; Faas, B.H.W.
2016-01-01
OBJECTIVE: To validate Illumina's two-channel NextSeq 500 sequencing system for noninvasive prenatal testing (NIPT) of fetal whole chromosome and partial aberrations. METHODS: A total of 162 plasma samples, previously sequenced for NIPT on a SOLiD 5500xl platform, were sequenced on the NextSeq 500 u
van Rooij, Linda G. M.; de Vries, Linda S.; van Huffelen, Alexander C.; Toet, Mona C.
2010-01-01
Background Amplitude integrated electroencephalography (aEEG) is a valuable tool for evaluating neonatal encephalopathy and identifying electrographic seizures. Objective To compare seizure activity and background pattern (BGP) between one-channel and two-channel aEEG recordings in full-term neonate
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...
DEFF Research Database (Denmark)
Santocanale, Luigi
2002-01-01
A μ-lattice is a lattice with the property that every unary polynomial has both a least and a greatest fix-point. In this paper we define the quasivariety of μ-lattices and, for a given partially ordered set P, we construct a μ-lattice JP whose elements are equivalence classes of games in a preor...
Comparative dynamics of the two channels of the reaction of D + MuH.
Aoiz, F J; Aldegunde, J; Herrero, V J; Sáez-Rábanos, V
2014-06-07
thermal cumulative reaction probabilities of the two channels indicates that at the lowest energies/temperatures the reaction into the DH + Mu channel takes place via'leakage' from collisions proceeding along the DMu + H reaction path.
Design of two-channel oscilloscope and basic circuit simulations in LabView
Balzhiev, Plamen; Makal, Jaroslaw
2008-01-01
The project is realized as a diploma thesis in Bialystok Technical University, Poland). The main aim is to develop a useful educational tool which presents the time and frequency characteristics in basic electrical circuits. It is designed as a helpful instrument for lectures and laboratory classes. The predominant audience will be students of electrical engineering from first semester of the higher education. Therefore the level of knowledge at this stage of education is not high enough and different techniques are necessary to increase the students' interest and the efficiency of teaching process. This educational instrument provides the needed knowledge concerning the basic circuits and its parameters. Graphics and animations of the general processes in the electrical circuits make the problems more interesting, comprehensive and easier to understand. For designing such an instrument the National Instruments' programming environment LabView is used. It is preferred to the other simulation software because of its simplicity flexibility and also availability (the free demo version is sufficient to make a simple virtual instrument). LabView uses graphical programming language and has powerful mathematical functions for analysis and simulations. The useful visualization tools for presenting different diagrams are worth recommending, too. It is also specialized in measurement and control and it supports a wide variety of hardware. Therefore this software is suitable for laboratory classes to present the dependencies between the simulated characteristics in basic electrical circuits and the real one measured with the hardware device. For this purpose a two-channel oscilloscope is designed as part of the described project. The main purpose of this instrument as part of the educational process is to present the desired characteristics of the electrical circuits and to become familiar with the general functions of the oscilloscope. This project combines several important
Energy Technology Data Exchange (ETDEWEB)
Anderson, Iain [U.S. Department of Energy, Joint Genome Institute; Teshima, Hazuki [Los Alamos National Laboratory (LANL); Nolan, Matt [U.S. Department of Energy, Joint Genome Institute; Lapidus, Alla L. [U.S. Department of Energy, Joint Genome Institute; Tice, Hope [U.S. Department of Energy, Joint Genome Institute; Glavina Del Rio, Tijana [U.S. Department of Energy, Joint Genome Institute; Cheng, Jan-Fang [U.S. Department of Energy, Joint Genome Institute; Han, Cliff [Los Alamos National Laboratory (LANL); Tapia, Roxanne [Los Alamos National Laboratory (LANL); Goodwin, Lynne A. [Los Alamos National Laboratory (LANL); Pitluck, Sam [U.S. Department of Energy, Joint Genome Institute; Liolios, Konstantinos [U.S. Department of Energy, Joint Genome Institute; Mavromatis, K [U.S. Department of Energy, Joint Genome Institute; Pagani, Ioanna [U.S. Department of Energy, Joint Genome Institute; Ivanova, N [U.S. Department of Energy, Joint Genome Institute; Mikhailova, Natalia [U.S. Department of Energy, Joint Genome Institute; Pati, Amrita [U.S. Department of Energy, Joint Genome Institute; Chen, Amy [U.S. Department of Energy, Joint Genome Institute; Palaniappan, Krishna [U.S. Department of Energy, Joint Genome Institute; Land, Miriam L [ORNL; Rohde, Manfred [HZI - Helmholtz Centre for Infection Research, Braunschweig, Germany; Lang, Elke [DSMZ - German Collection of Microorganisms and Cell Cultures GmbH, Braunschweig, Germany; Detter, J. Chris [U.S. Department of Energy, Joint Genome Institute; Goker, Markus [DSMZ - German Collection of Microorganisms and Cell Cultures GmbH, Braunschweig, Germany; Woyke, Tanja [U.S. Department of Energy, Joint Genome Institute; Bristow, James [U.S. Department of Energy, Joint Genome Institute; Eisen, Jonathan [U.S. Department of Energy, Joint Genome Institute; Markowitz, Victor [U.S. Department of Energy, Joint Genome Institute; Hugenholtz, Philip [U.S. Department of Energy, Joint Genome Institute; Kyrpides, Nikos C [U.S. Department of Energy, Joint Genome Institute; Klenk, Hans-Peter [DSMZ - German Collection of Microorganisms and Cell Cultures GmbH, Braunschweig, Germany
2013-01-01
rateuria aurantia (ex Kondo and Ameyama 1958) Swings et al. 1980 is a member of the bispecific genus Frateuria in the family Xanthomonadaceae, which is already heavily targeted for non-type strain genome sequencing. Strain Kondo 67(T) was initially (1958) identified as a member of 'Acetobacter aurantius', a name that was not considered for the approved list. Kondo 67(T) was therefore later designated as the type strain of the newly proposed acetogenic species Frateuria aurantia. The strain is of interest because of its triterpenoids (hopane family). F. aurantia Kondo 67(T) is the first member of the genus Frateura whose genome sequence has been deciphered, and here we describe the features of this organism, together with the complete genome sequence and annotation. The 3,603,458-bp long chromosome with its 3,200 protein-coding and 88 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.
Theoretical study of Kondo effect and related transport properties in topological insulator systems
Xin, Xianhao
This thesis presents theoretical studies of the Kondo effect and related transport properties in topological insulator systems. The thesis mainly covers two topics: the Kondo effect on the surface of a bulk topological insulator material and the Kondo effect in a topological insulator quantum dot. Other relevant background knowledge and theoretical techniques for the transport calculations are also discussed in the thesis. For the first topic, we investigate the role of magnetic impurities in the transport properties of a three-dimensional topological insulator's surface states. First, we combine the second-order perturbation theory and the Boltzmann transport equation to calculate the magnetically induced resistivity in a topological insulator. Our result shows a non-perturbative behavior when conduction electrons and magnetic impurities' spins are antiferromagnetically coupled. The surface resistivity is found to display an oscillatory rather than isotropic behavior compared to the conventional Kondo effect. Both the variational method and renormalization group (RG) analysis are employed to compute the Kondo temperature, through which the non-perturbative behavior is confirmed. We further study the RG flows and demonstrate that the RG trajectories eventually flow into a strong coupling regime if the coupling is antiferromagnetic. This work is motivated by the recent transport experiments, in which surface currents were detected in topological insulators. The calculation is shown to be qualitatively consistent with the low temperature dip observed in the experimental R - T curve, and it might be one of the possible origins of the dip. For the second main topic, we investigate theoretically the nonequilibrium transport properties of a topological insulator quantum dot (TIQD) in the Coulomb blockade and Kondo regime. An Anderson impurity model is applied to a TIQD system coupled to two external leads, and we show that the model realizes the spin-orbital Kondo effect
Wysokiński, Marcin M.; Kaczmarczyk, Jan; Spałek, Jozef
2015-09-01
The recently proposed diagrammatic expansion (DE) technique for the full Gutzwiller wave function (GWF) is applied to the Anderson lattice model. This approach allows for a systematic evaluation of the expectation values with full Gutzwiller wave function in finite-dimensional systems. It introduces results extending in an essential manner those obtained by means of the standard Gutzwiller approximation (GA), which is variationally exact only in infinite dimensions. Within the DE-GWF approach we discuss the principal paramagnetic properties and their relevance to heavy-fermion systems. We demonstrate the formation of an effective, narrow f band originating from atomic f -electron states and subsequently interpret this behavior as a direct itineracy of f electrons; it represents a combined effect of both the hybridization and the correlations induced by the Coulomb repulsive interaction. Such a feature is absent on the level of GA, which is equivalent to the zeroth order of our expansion. Formation of the hybridization- and electron-concentration-dependent narrow f band rationalizes the common assumption of such dispersion of f levels in the phenomenological modeling of the band structure of CeCoIn5. Moreover, it is shown that the emerging f -electron direct itineracy leads in a natural manner to three physically distinct regimes within a single model that are frequently discussed for 4 f - or 5 f -electron compounds as separate model situations. We identify these regimes as (i) the mixed-valence regime, (ii) Kondo/almost-Kondo insulating regime, and (iii) the Kondo-lattice limit when the f -electron occupancy is very close to the f -state half filling, →1 . The nonstandard features of the emerging correlated quantum liquid state are stressed.
Knolle, Johannes; Cooper, Nigel R
2017-03-03
Kondo insulating materials lie outside the usual dichotomy of weakly versus correlated-band versus Mott-insulators. They are metallic at high temperatures but resemble band insulators at low temperatures because of the opening of an interaction-induced band gap. The first discovered Kondo insulator (KI) SmB_{6} has been predicted to form a topological KI (TKI). However, since its discovery thermodynamic and transport anomalies have been observed that have defied a theoretical explanation. Enigmatic signatures of collective modes inside the charge gap are seen in specific heat, thermal transport, and quantum oscillation experiments in strong magnetic fields. Here, we show that TKIs are susceptible to the formation of excitons and magnetoexcitons. These charge neutral composite particles can account for long-standing anomalies in SmB_{6}.
Magnetic field effects on the DOS of a Kondo quantum dot coupled to LL leads
Yang, Kai-Hua; Qin, Chang-Dong; Wang, Huai-Yu; Wang, Xu
2017-01-01
We investigate the joint effects of a magnetic field and electron-electron interaction on the tunneling density of states (DOS) of a quantum dot coupled to the Luttinger liquid leads in the Kondo regime. We find that for intralead electron interaction, the DOS develops two peaks deviated from the origin by the Zeeman energy. With the increase of the intralead interaction, a phase transition occurs. For moderately strong interaction, the Zeeman splitting peaks develop into two dips. The splitting of the Kondo peak and dip is not symmetric with respect to up and down spins. In the limit of strong interaction the Zeeman splitting behavior disappears and there appears a power-law scaling behavior.
Jahn-Teller / Kondo Interplay in a Three-Terminal Quantum Dot
Toonen, R. C.; Qin, H.; Huettel, A. K.; Goswami, S.; van der Weide, D. W.; Eberl, K.; Blick, R. H.
2006-03-01
The Jahn-Teller effect is the spontaneous geometric distortion of a nonlinear molecular entity. The Kondo effect, an expression of asymptotic freedom, arises from the hybridization between localized states of a magnetic impurity and the itinerant states of its environment. The interplay of these two phenomena has attracted the attention of theorists studying the growth and interactions of heavy-fermion systems. Because of the technical difficulties associated with probing isolated impurities in bulk materials, this composite effect has remained experimentally unexplored. We have investigated co-tunneling transport phenomena in a three-terminal quantum dot with triangular symmetry. Our measurements of anomalous spectral signatures reveal interplay between the Jahn-Teller and Kondo effects. This discovery suggests a means of controlling the correlation of spatially separated pairs of entangled electrons (EPR pairs)---a necessary condition for the physical realization of a quantum computer (DiVincenzo's 7th requirement).
Temperature dependence of the Kondo resonance and its satellites in CeCu2Si2.
Reinert, F; Ehm, D; Schmidt, S; Nicolay, G; Hüfner, S; Kroha, J; Trovarelli, O; Geibel, C
2001-09-03
We present high-resolution photoemission spectroscopy studies on the Kondo resonance of the strongly correlated Ce system CeCu2Si2. By exploiting the thermal broadening of the Fermi edge we analyze position, spectral weight, and temperature dependence of the low-energy 4f spectral features, whose major weight lies above the Fermi level E(F). We also present theoretical predictions based on the single-impurity Anderson model using an extended noncrossing approximation, including all spin-orbit and crystal field splittings of the 4f states. The excellent agreement between theory and experiment provides strong evidence that the spectral properties of CeCu2Si2 can be described by single-impurity Kondo physics down to T approximately 5 K.
Spin-spin correlations between two Kondo impurities coupled to an open Hubbard chain
Tiegel, A. C.; Dargel, P. E.; Hallberg, K. A.; Frahm, H.; Pruschke, T.
2013-02-01
In order to study the interplay between Kondo and Ruderman-Kittel-Kasuya-Yosida interaction, we calculate the spin-spin correlation functions between two Kondo impurities coupled to different sites of a half-filled open Hubbard chain. Using the density-matrix renormalization group (DMRG), we reexamine the exponents for the power-law decay of the correlation function between the two impurity spins as a function of the antiferromagnetic coupling J, the Hubbard interaction U, and the distance R between the impurities. The exponents for finite systems obtained in this work deviate from previously published DMRG calculations. We furthermore show that the long-distance behavior of the exponents is the same for impurities coupled to the bulk or to both ends of the chain. We note that a universal exponent for the asymptotic behavior can not be extracted from these finite-size systems with open boundary conditions.
4f heavy femion photoelectron spectra do not exhibit the Kondo scale
Energy Technology Data Exchange (ETDEWEB)
Arko, A.J.; Joyce, J.J.; Andrews, A.B.; Blyth, I.R.; Barlett, R.J.; Fisk, Z. [Los Alamos National Laboratory, NM (United States); Canfield, P.C.; Olson, C.G.; Benning, P.J. [Iowa Sate Univ., Ames, IA (United States); Poirier, D.M.; Weaver, J.H. [Univ. of Minnesota, Minneapolis, MN (United States); Riseborough, P.S. [Polytechnic Univ., Brookyln, NY (United States)
1994-12-31
It has been the authors contention for some time that the Single Impurity Anderson Model (SIAM), as extended by Gunnarsson and Schonhammer (GS), or the non-crossing approximation (NCA), does not correctly describe the 4f photoelectron spectra of heavy fermions. Recently they have concentrated on Yb heavy fermions since in these materials the Kondo resonance (KR) is fully occupied and thus accessible via photoemission. In particular, they have repeatedly pointed out that the width, position, spectral weight, lineshape, and temperature dependence of the features assumed to be the KR and its sidebands, are nearly independent of the Kondo temperature, T{sub K}, while at the same time bearing a striking resemblance to the simple 4f core level spectra of pure Yb metal, or of Lu isostructural Lu compounds. It is important to resolve these issues in view of the fundamental nature of the problem.
Interplay between the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida interaction.
Prüser, Henning; Dargel, Piet E; Bouhassoune, Mohammed; Ulbrich, Rainer G; Pruschke, Thomas; Lounis, Samir; Wenderoth, Martin
2014-11-11
The interplay between the Ruderman-Kittel-Kasuya-Yosida interaction and the Kondo effect is expected to provide the driving force for the emergence of many phenomena in strongly correlated electron materials. Two magnetic impurities in a metal are the smallest possible system containing all these ingredients and define a bottom-up approach towards a long-term understanding of concentrated/dense systems. Here we report on the experimental and theoretical investigation of iron dimers buried below a Cu(100) surface by means of low-temperature scanning tunnelling spectroscopy combined with density functional theory and numerical renormalization group calculations. The Kondo effect, in particular the width of the Abrikosov-Suhl resonance, is strongly altered or even suppressed due to magnetic coupling between the impurities. It oscillates as a function of dimer separation revealing that it is related to indirect exchange interactions mediated by the conduction electrons.
Kondo-like zero-bias conductance anomaly in a three-dimensional topological insulator nanowire
Cho, Sungjae; Zhong, Ruidan; Schneeloch, John A.; Gu, Genda; Mason, Nadya
2016-02-01
Zero-bias anomalies in topological nanowires have recently captured significant attention, as they are possible signatures of Majorana modes. Yet there are many other possible origins of zero-bias peaks in nanowires—for example, weak localization, Andreev bound states, or the Kondo effect. Here, we discuss observations of differential-conductance peaks at zero-bias voltage in non-superconducting electronic transport through a 3D topological insulator (Bi1.33Sb0.67)Se3 nanowire. The zero-bias conductance peaks show logarithmic temperature dependence and often linear splitting with magnetic fields, both of which are signatures of the Kondo effect in quantum dots. We characterize the zero-bias peaks and discuss their origin.
Ionic Hamiltonians for transition metal atoms: effective exchange coupling and Kondo temperature
Flores, F.; Goldberg, E. C.
2017-02-01
An ionic Hamiltonian for describing the interaction between a metal and a d-shell transition metal atom having an orbital singlet state is introduced and its properties analyzed using the Schrieffer-Wolf transformation (exchange coupling) and the poor man’s scaling method (Kondo temperature). We find that the effective exchange coupling between the metal and the atom has an antiferromagnetic or a ferromagnetic interaction depending on the kind of atomic fluctuations, either S\\to S-1/2 or S\\to S+1/2 , associated with the metal-atom coupling. We present a general scheme for all those processes and calculate, for the antiferromagnetic interaction, the corresponding Kondo-temperature.
Two Types of Pressure Dependence of Residual Resistivity in Doped Kondo Insulators
Institute of Scientific and Technical Information of China (English)
YUAN Yi-Zhe; LI Zheng-Zhong; XIAO Ming-Wen; XU Wang; XU Xiao-Hua
2004-01-01
The pressure dependence of the residual resistivity of the doped electron-type and hole-type Kondo insulators (KIs) are calculated within the framework of the slave-boson mean-field theory and the coherent potential approximation. It is shown that as the pressure increases, the resistivity increases and decreases for the dilute doping electron-type and hole-type KIs, respectively. These results are qualitatively in agreement with the experiments.
Campos, R G; Campos, Rafael G.; Tututi, Eduardo S.
2002-01-01
It is shown that the nonlocal Dirac operator yielded by a lattice model that preserves chiral symmetry and uniqueness of fields, approaches to an ultralocal and invariant under translations operator when the size of the lattice tends to zero.
New integrable lattice hierarchies
Energy Technology Data Exchange (ETDEWEB)
Pickering, Andrew [Area de Matematica Aplicada, ESCET, Universidad Rey Juan Carlos, c/ Tulipan s/n, 28933 Mostoles, Madrid (Spain); Zhu Zuonong [Departamento de Matematicas, Universidad de Salamanca, Plaza de la Merced 1, 37008 Salamanca (Spain) and Department of Mathematics, Shanghai Jiao Tong University, Shanghai 200030 (China)]. E-mail: znzhu2@yahoo.com.cn
2006-01-23
In this Letter we give a new integrable four-field lattice hierarchy, associated to a new discrete spectral problem. We obtain our hierarchy as the compatibility condition of this spectral problem and an associated equation, constructed herein, for the time-evolution of eigenfunctions. We consider reductions of our hierarchy, which also of course admit discrete zero curvature representations, in detail. We find that our hierarchy includes many well-known integrable hierarchies as special cases, including the Toda lattice hierarchy, the modified Toda lattice hierarchy, the relativistic Toda lattice hierarchy, and the Volterra lattice hierarchy. We also obtain here a new integrable two-field lattice hierarchy, to which we give the name of Suris lattice hierarchy, since the first equation of this hierarchy has previously been given by Suris. The Hamiltonian structure of the Suris lattice hierarchy is obtained by means of a trace identity formula.
Spin fluctuations in the anisotropic Kondo insulator CeRu4 Sn6
Fuhrman, Wesley T.; Haenel, J.; Rodriguez, J.; Paschen, S.; Broholm, C. L.
We report and model anisotropic quasi-elastic magnetic neutron scattering from single crystalline CeRu4Sn6. For T ~ 2 K the magnetic neutron scattering is broad in momentum (Q) with a persistent 1 / ℏω spectrum throughout the Brillouin zone. This indicates a lack of spatial coherence and no characteristic energy scale beyond the 0.2 meV resolution of the measurement. We find the Q-dependence of the scattering can be modeled by a Kondo-Heisenberg Hamiltonian that describes residual carriers and incompletely compensated localized electrons. These findings support the interpretation of tetragonal CeRu4Sn6 as an anisotropic or nodal Kondo insulator, markedly different from typical cubic Kondo insulators. We further discuss potential topological implications. Work at IQM was supported by the U.S. Department of Energy, office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-08ER4654. W.T.F. thanks the ARCS foundation and Lockheed Martin for additional support.
Energy Technology Data Exchange (ETDEWEB)
Wang, Xiaoli; Hou, Dong, E-mail: houdong@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Zheng, Xiao, E-mail: xz58@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Institute of Applied Physics, Guizhou Normal College, Guiyang, Guizhou 550018 (China); Yan, YiJing [Hefei National Laboratory for Physical Sciences at the Microscale, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), University of Science and Technology of China, Hefei, Anhui 230026 (China); Department of Chemistry, Hong Kong University of Science and Technology, Hong Kong (China)
2016-01-21
The magnetic anisotropy and Kondo phenomena in a mechanically stretched magnetic molecular junction are investigated by combining the density functional theory (DFT) and hierarchical equations of motion (HEOM) approach. The system is comprised of a magnetic complex Co(tpy–SH){sub 2} sandwiched between adjacent gold electrodes, which is mechanically stretched in experiments done by Parks et al. [Science 328, 1370 (2010)]. The electronic structure and mechanical property of the stretched system are investigated via the DFT calculations. The HEOM approach is then employed to characterize the Kondo resonance features, based on the Anderson impurity model parameterized from the DFT results. It is confirmed that the ground state prefers the S = 1 local spin state. The structural properties, the magnetic anisotropy, and corresponding Kondo peak splitting in the axial stretching process are systematically evaluated. The results reveal that the strong electron correlations and the local magnetic properties of the molecule magnet are very sensitive to structural distortion. This work demonstrates that the combined DFT+HEOM approach could be useful in understanding and designing mechanically controlled molecular junctions.
Theory of scanning tunneling spectroscopy: from Kondo impurities to heavy fermion materials
Morr, Dirk K.
2017-01-01
Kondo systems ranging from the single Kondo impurity to heavy fermion materials present us with a plethora of unconventional properties whose theoretical understanding is still one of the major open problems in condensed matter physics. Over the last few years, groundbreaking scanning tunneling spectroscopy (STS) experiments have provided unprecedented new insight into the electronic structure of Kondo systems. Interpreting the results of these experiments—the differential conductance and the quasi-particle interference spectrum—however, has been complicated by the fact that electrons tunneling from the STS tip into the system can tunnel either into the heavy magnetic moment or the light conduction band states. In this article, we briefly review the theoretical progress made in understanding how quantum interference between these two tunneling paths affects the experimental STS results. We show how this theoretical insight has allowed us to interpret the results of STS experiments on a series of heavy fermion materials providing detailed knowledge of their complex electronic structure. It is this knowledge that is a conditio sine qua non for developing a deeper understanding of the fascinating properties exhibited by heavy fermion materials, ranging from unconventional superconductivity to non-Fermi-liquid behavior in the vicinity of quantum critical points.
Kondo physics of the Anderson impurity model by distributional exact diagonalization
Motahari, S.; Requist, R.; Jacob, D.
2016-12-01
The distributional exact diagonalization (DED) scheme is applied to the description of Kondo physics in the Anderson impurity model. DED maps Anderson's problem of an interacting impurity level coupled to an infinite bath onto an ensemble of finite Anderson models, each of which can be solved by exact diagonalization. An approximation to the self-energy of the original infinite model is then obtained from the ensemble-averaged self-energy. Using Friedel's sum rule, we show that the particle number constraint, a central ingredient of the DED scheme, ultimately imposes Fermi liquid behavior on the ensemble-averaged self-energy, and thus is essential for the description of Kondo physics within DED. Using the numerical renormalization group (NRG) method as a benchmark, we show that DED yields excellent spectra, both inside and outside the Kondo regime for a moderate number of bath sites. Only for very strong correlations (U /Γ ≫10 ) does the number of bath sites needed to achieve good quantitative agreement become too large to be computationally feasible.
Magnetic-field-induced mixed-level Kondo effect in two-level systems
Energy Technology Data Exchange (ETDEWEB)
Wong, Arturo; Ngo, Anh T.; Ulloa, Sergio E.
2016-10-17
We consider a two-orbital impurity system with intra-and interlevel Coulomb repulsion that is coupled to a single conduction channel. This situation can generically occur in multilevel quantum dots or in systems of coupled quantum dots. For finite energy spacing between spin-degenerate orbitals, an in-plane magnetic field drives the system from a local-singlet ground state to a "mixed-level" Kondo regime, where the Zeeman-split levels are degenerate for opposite-spin states. We use the numerical renormalization group approach to fully characterize this mixed-level Kondo state and discuss its properties in terms of the applied Zeeman field, temperature, and system parameters. Under suitable conditions, the total spectral function is shown to develop a Fermi-level resonance, so that the linear conductance of the system peaks at a finite Zeeman field while it decreases as a function of temperature. These features, as well as the local moment and entropy contribution of the impurity system, are commensurate with Kondo physics, which can be studied in suitably tuned quantum dot systems.
Photoemission and the electronic properties of heavy fermions -- limitations of the Kondo model
Energy Technology Data Exchange (ETDEWEB)
Joyce, J.J.; Arko, A.J.; Andrews, A.B. [and others
1993-09-01
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{sub 2}Si{sub 2}, YbAgCu{sub 4} and YbAl{sub 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{sub 3}, the heavy fermion materials show no substantive spectroscopic differences from simple 4f levels observed in Yb metal and LuAl{sub 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.
Photoemission and the electronic properties of heavy fermions - limitations of the Kondo model
Energy Technology Data Exchange (ETDEWEB)
Joyce, J.J. [Los Alamos Nat. Lab., NM (United States); Arko, A.J. [Los Alamos Nat. Lab., NM (United States); Andrews, A.B. [Los Alamos Nat. Lab., NM (United States); Blyth, R.I.R. [Los Alamos Nat. Lab., NM (United States); Bartlett, R.J. [Los Alamos Nat. Lab., NM (United States); Thompson, J.D. [Los Alamos Nat. Lab., NM (United States); Fisk, Z. [Los Alamos Nat. Lab., NM (United States); Riseborough, P.S. [Polytechnic Institute of New York, Department of Physics, Brooklyn, NY 11201 (United States); Canfield, P.C. [Ames Laboratory USDOE, Ames, IA 50011 (United States); Olson, C.G. [Ames Laboratory USDOE, Ames, IA 50011 (United States); Benning, P.J. [Ames Laboratory USDOE, Ames, IA 50011 (United States)
1995-03-01
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 significant disagreement with the Kondo model predictions (as calculated within the Gunnarsson-Schonhammer computational method). Moreover, the Yb heavy fermion photoemission spectra give strong indications of core-like characteristics and compare favorably to purely divalent Yb metal and core-like Lu 4f levels. The heavy fermions YbCu{sub 2}Si{sub 2}, YbAgCu{sub 4} and YbAl{sub 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{sub 3}. The heavy fermion materials show no substantive spectroscopic differences from 4f levels observed in Yb metal and LuAl{sub 3}. Also, the variation with temperature of the 4f lineshape 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. ((orig.)).
Kondo screening in two-dimensional p -type transition-metal dichalcogenides
Phillips, Michael; Aji, Vivek
2017-02-01
Systems with strong spin-orbit coupling support a number of new phases of matter and novel phenomena. This work focuses on the interplay of spin-orbit coupling and interactions in yielding correlated phenomena in two-dimensional transition-metal dichalcogenides. In particular we explore the physics of Kondo screening resulting from the lack of centrosymmetry, large spin splitting, and spin valley locking in hole-doped systems. The key ingredients are (i) valley-dependent spin-momentum locking perpendicular to the two-dimensional crystal, (ii) a single nondegenerate Fermi surface per valley, and (iii) nontrivial Berry curvature associated with the low-energy bands. The resulting Kondo resonance has a finite-triplet component and nontrivial momentum space structure which facilitates new approaches to both probing and manipulating the correlated state. Using a variational wave function and the numerical renormalization group approaches we study the nature of the Kondo resonance both in the absence and presence of circularly polarized light. The latter induces an imbalance in the population of the two valleys leading to novel magnetic phenomena in the correlated state.
Kanazawa, Takuya
2016-01-01
We study the interplay between the Kondo effect and (color) superconductivity in doped Dirac metals with magnetic impurities and in quark matter with colorful impurities. We first point out that the overscreened Kondo effect arises in the normal state of these systems. Next the (color) superconducting gap is incorporated as a mean field and the phase diagram for a varying gap and temperature is constructed nonperturbatively. A rich phase structure emerges from a competition of effects unique to a multichannel system. The Kondo-screened phase is shown to disappear for a sufficiently large gap. Peculiarity of quark matter due to the confining property of non-Abelian gauge fields is noted. We also investigate the spectrum of sub-gap excited states, called Shiba states. Based on a model calculation and physical reasoning we predict that, as the coupling of the impurity to the bulk is increased, there will be more than one quantum phase transition due to level crossing among overscreened states.
Sober Topological Molecular Lattices
Institute of Scientific and Technical Information of China (English)
张德学; 李永明
2003-01-01
A topological molecular lattice (TML) is a pair (L, T), where L is a completely distributive lattice and r is a subframe of L. There is an obvious forgetful functor from the category TML of TML's to the category Loc of locales. In this note,it is showed that this forgetful functor has a right adjoint. Then, by this adjunction,a special kind of topological molecular lattices called sober topological molecular lattices is introduced and investigated.
Atkinson, D; van Steenwijk, F.J.
The resistance between two arbitrary nodes in an infinite square lattice of:identical resistors is calculated, The method is generalized to infinite triangular and hexagonal lattices in two dimensions, and also to infinite cubic and hypercubic lattices in three and more dimensions. (C) 1999 American
Lattice Regularization and Symmetries
Hasenfratz, Peter; Von Allmen, R; Allmen, Reto von; Hasenfratz, Peter; Niedermayer, Ferenc
2006-01-01
Finding the relation between the symmetry transformations in the continuum and on the lattice might be a nontrivial task as illustrated by the history of chiral symmetry. Lattice actions induced by a renormalization group procedure inherit all symmetries of the continuum theory. We give a general procedure which gives the corresponding symmetry transformations on the lattice.
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.
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.
Sarkar, T P; Gopinadhan, K; Motapothula, M; Saha, S; Huang, Z; Dhar, S; Patra, A; Lu, W M; Telesio, F; Pallecchi, I; Ariando; Marré, D; Venkatesan, T
2015-08-12
We report the observation of spatially separated Kondo scattering and ferromagnetism in anatase Ta0.06Ti0.94O2 thin films as a function of thickness (10-200 nm). The Kondo behavior observed in thicker films is suppressed on decreasing thickness and vanishes below ~25 nm. In 200 nm film, transport data could be fitted to a renormalization group theory for Kondo scattering though the carrier density in this system is lower by two orders of magnitude, the magnetic entity concentration is larger by a similar magnitude and there is strong electronic correlation compared to a conventional system such as Cu with magnetic impurities. However, ferromagnetism is observed at all thicknesses with magnetic moment per unit thickness decreasing beyond 10 nm film thickness. The simultaneous presence of Kondo and ferromagnetism is explained by the spatial variation of defects from the interface to surface which results in a dominantly ferromagnetic region closer to substrate-film interface while the Kondo scattering is dominant near the surface and decreasing towards the interface. This material system enables us to study the effect of neighboring presence of two competing magnetic phenomena and the possibility for tuning them.
Anomalous ferromagnetism in CeRh3B2: Possibility of a new Kondo-lattice state
Shaheen, S. A.; Schilling, J. S.; Shelton, R. N.
1985-01-01
Information on the nature of the highly anomalous ferromagnetic state of CeRh3B2 below 115 K is gained by studying the evolution of the magnetic, superconducting, and structural properties across the quasiternary series LaxCe1-xRh3B2 and Ce(RuyRh1-y)3B2. The present results offer considerable evidence that this ferromagnetism originates from the ordering of Ce local moments and not, as has been claimed, from itinerant magnetism in the Rh 4d band.
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.
Ikezoe, R.; Ichimura, M.; Itagaki, J.; Hirata, M.; Sumida, S.; Jang, S.; Izumi, K.; Tanaka, A.; Yoshikawa, M.; Kohagura, J.; Sakamoto, M.; Nakashima, Y.
2016-10-01
A two-channel microwave reflectometer with capability of fast switching of microwave antennas in array was developed and applied to a hot linear plasma produced in GAMMA 10 to study the behavior of Alfvén waves in a collisionless bounded plasma. High-frequency fluctuations associated with Alfvén-ion-cyclotron (AIC) waves were successfully measured at multi points using this system. It is found that coherent phase fluctuations are obtainable at wide radial and axial region for the AIC waves. In addition, measured phase-difference profile clearly shows standing wave structures. Signature of movement of these nodes is also obtained. These results demonstrate applicability of the developed two-channel reflectometer for assessment of spatial structure of high-frequency waves and also verifies globally expanded coherent structure of the AIC waves in GAMMA 10. Two-point correlation analysis in conjunction with multi-point measurements using antenna switching turns out to be a powerful tool for investigating spatial structure of waves in a hot plasma where traditional solid probes are inadequate. This work was in part supported by Grant-in-Aid for Young Scientists (B) (15K17797) and Scientific Research (C) (25400531), and by Bidirectional Collaborative Research Program of NIFS (NIFS15KUGM101).
Rotter, Ana; Hren, Matjaz; Baebler, Spela; Blejec, Andrej; Gruden, Kristina
2008-09-01
Due to the great variety of preprocessing tools in two-channel expression microarray data analysis it is difficult to choose the most appropriate one for a given experimental setup. In our study, two independent two-channel inhouse microarray experiments as well as a publicly available dataset were used to investigate the influence of the selection of preprocessing methods (background correction, normalization, and duplicate spots correlation calculation) on the discovery of differentially expressed genes. Here we are showing that both the list of differentially expressed genes and the expression values of selected genes depend significantly on the preprocessing approach applied. The choice of normalization method to be used had the highest impact on the results. We propose a simple but efficient approach to increase the reliability of obtained results, where two normalization methods which are theoretically distinct from one another are used on the same dataset. Then the intersection of results, that is, the lists of differentially expressed genes, is used in order to get a more accurate estimation of the genes that were de facto differentially expressed.
Spontaneous formation of kagome network and Dirac half-semimetal on a triangular lattice
Akagi, Yutaka; Motome, Yukitoshi
2015-04-01
In spin-charge coupled systems, geometrical frustration of underlying lattice structures can give rise to nontrivial magnetic orders and electronic states. Here we explore such a possibility in the Kondo lattice model with classical localized spins on a triangular lattice by using a variational calculation and simulated annealing. We find that the system exhibits a four-sublattice collinear ferrimagnetic phase at 5/8 filling for a large Hund's-rule coupling. In this state, the system spontaneously differentiates into the up-spin kagome network and the isolated down-spin sites, which we call the kagome network formation. In the kagome network state, the system becomes Dirac half-semimetallic: The electronic structure shows a massless Dirac node at the Fermi level, and the Dirac electrons are almost fully spin polarized due to the large Hund's-rule coupling. We also study the effect of off-site Coulomb repulsion in the kagome network phase where the system is effectively regarded as a 1/3-filling spinless fermion system on the kagome lattice. We find that, at the level of the mean-field approximation, a √{3 }×√{3 } -type charge order occurs in the kagome network state, implying the possibility of fractional charge excitations in this triangular lattice system. Moreover, we demonstrate that the kagome network formation with fully polarized Dirac electrons are controllable by an external magnetic field.
The $B\\to K^*$ form factors on the lattice
Agadjanov, Andria; Meißner, Ulf-G; Rusetsky, Akaki
2016-01-01
The extraction of the $B\\to K^*$ transition form factors from lattice data is studied, applying non-relativistic effective field theory in a finite volume. The possible mixing of $\\pi K$ and $\\eta K$ states is taken into account. The two-channel analogue of the Lellouch-L\\"uscher formula is reproduced. Due to the resonance nature of the $K^*$, an equation is derived, which allows to determine the form factors at the pole position in a process-independent manner. The infinitely-narrow width approximation of the results is discussed.
Kondo Hybridization and the Origin of Metallic States at the (001 Surface of SmB_{6}
Directory of Open Access Journals (Sweden)
E. Frantzeskakis
2013-12-01
Full Text Available SmB_{6}, a well-known Kondo insulator, has been proposed to be an ideal topological insulator with states of topological character located in a clean, bulk electronic gap, namely, the Kondo-hybridization gap. Since the Kondo gap arises from many-body electronic correlations, SmB_{6} would be placed at the head of a new material class: topological Kondo insulators. Here, for the first time, we show that the k-space characteristics of the Kondo-hybridization process is the key to unraveling the origin of the two types of metallic states experimentally observed by angle-resolved photoelectron spectroscopy (ARPES in the electronic band structure of SmB_{6}(001. One group of these states is essentially of bulk origin and cuts the Fermi level due to the position of the chemical potential 20 meV above the lowest-lying 5d-4f hybridization zone. The other metallic state is more enigmatic, being weak in intensity, but represents a good candidate for a topological surface state. However, before this claim can be substantiated by an unequivocal measurement of its massless dispersion relation, our data raise the bar in terms of the ARPES resolution required, as we show there to be a strong renormalization of the hybridization gaps by a factor 2–3 compared to theory, following from the knowledge of the true position of the chemical potential and a careful comparison with the predictions from recent local-density-approximation (LDA+Gutzwiller calculations. All in all, these key pieces of evidence act as triangulation markers, providing a detailed description of the electronic landscape in SmB_{6} and pointing the way for future, ultrahigh-resolution ARPES experiments to achieve a direct measurement of the Dirac cones in the first topological Kondo insulator.
Jammed lattice sphere packings
Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore
2013-01-01
We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a...
On Traveling Waves in Lattices: The Case of Riccati Lattices
Dimitrova, Zlatinka
2012-09-01
The method of simplest equation is applied for analysis of a class of lattices described by differential-difference equations that admit traveling-wave solutions constructed on the basis of the solution of the Riccati equation. We denote such lattices as Riccati lattices. We search for Riccati lattices within two classes of lattices: generalized Lotka-Volterra lattices and generalized Holling lattices. We show that from the class of generalized Lotka-Volterra lattices only the Wadati lattice belongs to the class of Riccati lattices. Opposite to this many lattices from the Holling class are Riccati lattices. We construct exact traveling wave solutions on the basis of the solution of Riccati equation for three members of the class of generalized Holling lattices.
Energy Technology Data Exchange (ETDEWEB)
Shindler, A. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC
2007-07-15
I review the theoretical foundations, properties as well as the simulation results obtained so far of a variant of the Wilson lattice QCD formulation: Wilson twisted mass lattice QCD. Emphasis is put on the discretization errors and on the effects of these discretization errors on the phase structure for Wilson-like fermions in the chiral limit. The possibility to use in lattice simulations different lattice actions for sea and valence quarks to ease the renormalization patterns of phenomenologically relevant local operators, is also discussed. (orig.)
Modulated Spin Liquid and Magnetic Order from a Kondo-Heisenberg model applied to $URu_{2}Si_{2}$
Montiel, Xavier; Burdin, Sébastien; Pépin, Catherine; Ferraz, Alvaro
2013-01-01
International audience; Using the Kondo-Heisenberg model framework, we analyze the effect of charge fluctuations in the modulated spin liquid (MSL) and in the antiferromagnetic (AF) ordering which were introduced by Pépin et al. [Phys. Rev. Lett. 106, 106601 (2011)] and Thomas et al. [Phys. Rev. B 87, 014422 (2013)]. Coupling the spin liquid to the charge sector enables us to discuss the formation of the Kondo effect in this system. As a result, we are able to observe the emergence of two pha...
Eckle, H. -P.; Johannesson, H.; Stafford, C. A.
2000-01-01
We study the persistent currents induced by both the Aharonov-Bohm and Aharonov-Casher effects in a one-dimensional mesoscopic ring coupled to a side-branch quantum dot at Kondo resonance. For privileged values of the Aharonov-Bohm-Casher fluxes, the problem can be mapped onto an integrable model, exactly solvable by a Bethe ansatz. In the case of a pure magnetic Aharonov-Bohm flux, we find that the presence of the quantum dot has no effect on the persistent current. In contrast, the Kondo re...
National Research Council Canada - National Science Library
Zhou, Qian; Tang, Cheng; Zhao, Ke-Wei; Xiong, Yan-Li; Chen, Shu; Xu, Wen-Jing; Lei, Xin
2016-01-01
The aim of this study was to determine the efficacy of 252Californium neutron intracavitary brachytherapy using a two-channel Y applicator combined with external beam radiotherapy for the treatment of endometrial cancer...
Institute of Scientific and Technical Information of China (English)
WU Shao-Quan; SUN Wei-Li
2007-01-01
Using the Keldysh Nonequilibrium Green function and equation-of-motion technique,we investigate Fano versus Kondo resonances in closed Aharonov-Bohm interferometer coupled to ferromagnetic leads and study their effects on the conductance of this system.The conductance with both parallel and antiparallel lead-polarization alignments is analysed for various values of the magnetic flux.Our results show that this system can provide an excellent spin filtering property,and a large tunnelling magnetoresistance can arise by adjusting the system parameters,which indicates that this system is a possible candidate for spin valve transistors and has important applications in spintronics.
Pressure-Resistant Intermediate Valence in the Kondo Insulator SmB_{6}.
Butch, Nicholas P; Paglione, Johnpierre; Chow, Paul; Xiao, Yuming; Marianetti, Chris A; Booth, Corwin H; Jeffries, Jason R
2016-04-15
Resonant x-ray emission spectroscopy was used to determine the pressure dependence of the f-electron occupancy in the Kondo insulator SmB_{6}. Applied pressure reduces the f occupancy, but surprisingly, the material maintains a significant divalent character up to a pressure of at least 35 GPa. Thus, the closure of the resistive activation energy gap and onset of magnetic order are not driven by stabilization of an integer valent state. Over the entire pressure range, the material maintains a remarkably stable intermediate valence that can in principle support a nontrivial band structure.
Temperature dependence of the Kondo resonance and its satellites in CeCu_2Si_2
Reinert, F.; Ehm, D.; Schmidt, S; Nicolay, G.; H"ufner, S.; Kroha, J.; Trovarelli, O.; Geibel, C.
2001-01-01
We present high-resolution photoemission spectroscopy studies on the Kondo resonance of the strongly-correlated Ce system CeCu$_2$Si$_2$. Exploiting the thermal broadening of the Fermi edge we analyze position, spectral weight, and temperature dependence of the low-energy 4f spectral features, whose major weight lies above the Fermi level $E_F$. We also present theoretical predictions based on the single-impurity Anderson model using an extended non-crossing approximation (NCA), including all...
Spontaneous Polarization of Kondo problem associated with Higher-spin analog of the 6-vertex model
Fukushima, N
1999-01-01
We study Kondo-type model associated with an integrable Higher-spin analog of the 6-vertex mode, which is constructed by inserting a spin 1/2 to spin 1 lines: $... C^3 \\otimes C^3 \\otimes C^2 \\otimes C^3 \\otimes C^3 ... .$ We formulate the problem in terms of representation theory of quantum affine algebra $U_q(\\hat{sl_2})$. We derive an exact formula of the spontaneous staggered polarization for our model, which corresponds to Baxter's formula for the 6-vertex model.
Scanning Gate Microscopy of Kondo Dots: Fabry-P\\'erot Interferences and Thermally Induced Rings
Kleshchonok, Andrii; Fleury, Geneviève; Pichard, Jean-Louis
2013-01-01
We study the conductance of an electron interferometer formed in a two dimensional electron gas between a nanostructured quantum contact and the charged tip of a scanning gate microscope. Measuring the conductance as a function of the tip position, thermally induced rings may be observed in addition to Fabry-P\\'erot interference fringes spaced by half the Fermi wavelength. If the contact is made of a quantum dot opened in the middle of a Kondo valley, we show how the location of the rings all...
Scanning Gate Microscopy of Kondo Dots: Fabry-Pérot Interferences and Thermally Induced Rings
Kleshchonok, Andrii; Fleury, Geneviève; Pichard, Jean-Louis
2013-01-01
5 pages, 4 figures; We study the conductance of an electron interferometer formed in a two dimensional electron gas between a nanostructured quantum contact and the charged tip of a scanning gate microscope. Measuring the conductance as a function of the tip position, thermally induced rings may be observed in addition to Fabry-Pérot interference fringes spaced by half the Fermi wavelength. If the contact is made of a quantum dot opened in the middle of a Kondo valley, we show how the locatio...
Fermi/non-Fermi mixing in SU($N$) Kondo effect
Kimura, Taro
2016-01-01
We apply conformal field theory analysis to the $k$-channel SU($N$) Kondo system, and find a peculiar behavior in the cases $N > k > 1$, which we call Fermi/non-Fermi mixing: The low temperature scaling is described as the Fermi liquid, while the zero temperature IR fixed point exhibits the non-Fermi liquid signature. We also show that the Wilson ratio is no longer universal for the cases $N > k > 1$. The deviation from the universal value of the Wilson ratio could be used as an experimental signal of the Fermi/non-Fermi mixing.
Magnetically tunable Kondo-Aharonov-Bohm effect in a triangular quantum dot.
Kuzmenko, T; Kikoin, K; Avishai, Y
2006-02-03
The role of discrete orbital symmetry in mesoscopic physics is manifested in a system consisting of three identical quantum dots forming an equilateral triangle. Under a perpendicular magnetic field, this system demonstrates a unique combination of Kondo and Aharonov-Bohm features due to an interplay between continuous [spin-rotation SU(2)] and discrete (permutation C3v) symmetries, as well as U(1) gauge invariance. The conductance as a function of magnetic flux displays sharp enhancement or complete suppression depending on contact setups.
Kikoin, K; Kiselev, M N; Wegewijs, M R
2006-05-05
We investigate transport through a mononuclear transition-metal complex with strong tunnel coupling to two electrodes. The ground state of this molecule is a singlet, while the first excited state is a triplet. We show that a modulation of the tunnel-barrier due to a molecular distortion which couples to the tunneling induces a Kondo-effect, provided the discrete vibrational energy compensates the singlet-triplet gap. We discuss the single-phonon and two-phonon-assisted cotunneling and possible experimental realization of the theory.
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.
Directory of Open Access Journals (Sweden)
Epelbaum E.
2010-04-01
Full Text Available We review recent progress on nuclear lattice simulations using chiral eﬀective ﬁeld theory. We discuss lattice results for dilute neutron matter at next-to-leading order, three-body forces at next-to-next-toleading order, isospin-breaking and Coulomb eﬀects, and the binding energy of light nuclei.
Phase diagram of the one-dimensional anisotropic Kondo-necklace model
Mahmoudian, S.; Langari, A.
2008-01-01
The one-dimensional anisotropic Kondo-necklace model has been studied by several methods. It is shown that a mean field approach fails to gain the correct phase diagram for the Ising-type anisotropy. We then applied the spin wave theory which is justified for the anisotropic case. We have derived the phase diagram between the antiferromagnetic long range order and the Kondo singlet phases. We have found that the exchange interaction (J) between the itinerant spins and local ones enhances the quantum fluctuations around the classical long range antiferromagnetic order and finally destroy the ordered phase at the critical value Jc . Moreover, our results show that the onset of anisotropy in the XY term of the itinerant interactions develops the antiferromagnetic order for J
Thermoelectric response of a correlated impurity in the nonequilibrium Kondo regime
Dorda, Antonius; Ganahl, Martin; Andergassen, Sabine; von der Linden, Wolfgang; Arrigoni, Enrico
2016-12-01
We study nonequilibrium thermoelectric transport properties of a correlated impurity connected to two leads for temperatures below the Kondo scale. At finite bias, for which a current flows across the leads, we investigate the differential response of the current to a temperature gradient. In particular, we compare the influence of a bias voltage and of a finite temperature on this thermoelectric response. This is of interest from a fundamental point of view to better understand the two different decoherence mechanisms produced by a bias voltage and by temperature. Our results show that in this respect the thermoelectric response behaves differently from the electric conductance. In particular, while the latter displays a similar qualitative behavior as a function of voltage and temperature, both in theoretical and experimental investigations, qualitative differences occur in the case of the thermoelectric response. In order to understand this effect, we analyze the different contributions in connection to the behavior of the impurity spectral function versus temperature. Especially in the regime of strong interactions and large enough bias voltages, we obtain a simple picture based on the asymmetric suppression or enhancement of the split Kondo peaks as a function of the temperature gradient. Besides the academic interest, these studies could additionally provide valuable information to assess the applicability of quantum dot devices as responsive nanoscale temperature sensors.
Possible undercompensation effect in the Kondo insulator (Yb,Tm)B12
Alekseev, P. A.; Nemkovski, K. S.; Mignot, J.-M.; Clementyev, E. S.; Ivanov, A. S.; Rols, S.; Bewley, R. I.; Filipov, V. B.; Shitsevalova, N. Yu.
2014-03-01
The effects of Tm substitution on the dynamical magnetic response of Yb1-xTmxB12 (x=0, 0.08, 0.15, and 0.75) and Lu0.92Tm0.08B12 compounds have been studied using time-of-flight inelastic neutron scattering. Major changes were observed in the spectral structure and temperature evolution of the Yb contribution to the inelastic response for a rather low content of magnetic Tm ions. A sizable influence of the RB12 host (YbB12, as compared to LuB12 or pure TmB12) on the crystal-field splitting of the Tm3+ ion is also reported. The results point to a specific effect of impurities carrying a magnetic moment (Tm, as compared to Lu or Zr) in a Kondo insulator, which is thought to reflect the "undercompensation" of Yb magnetic moments, originally Kondo screened in pure YbB12. A parallel is made with the strong effect of Tm substitution on the temperature dependence of the Seebeck coefficient in Yb1-xTmxB12, which was reported previously.
Keldysh effective action theory for universal physics in spin-(1)/(2) Kondo dots
Smirnov, Sergey; Grifoni, Milena
2013-03-01
We present a theory for the Kondo spin-(1)/(2) effect in strongly correlated quantum dots. The theory is applicable at any temperature and voltage. It is based on a quadratic Keldysh effective action parametrized by a universal function. We provide a general analytical form for the tunneling density of states through this universal function for which we propose a simple microscopic model. We apply our theory to the highly asymmetric Anderson model with U=∞ and describe its strong-coupling limit, weak-coupling limit, and crossover region within a single analytical expression. We compare our results with a numerical renormalization group in equilibrium and with a real-time renormalization group out of equilibrium and show that the universal shapes of the linear and differential conductance obtained in our theory and in these theories are very close to each other in a wide range of temperatures and voltages. In particular, as in the real-time renormalization group, we predict that at the Kondo voltage the differential conductance is equal to 2/3 of its maximum.
Institute of Scientific and Technical Information of China (English)
Niu Peng-Bin; Wang Qiang; Nie Yi-Hang
2013-01-01
The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn+2 ion (S =5/2) are investigated by the non-equilibrium Green function method.We consider a minimal model where the Mn-hole exchange coupling is strongly anisotropic so that spin-flip is suppressed and the impurity spin S and a hole spin s entering the quantum dot are coupled into spin pair states with (2S+ 1) sublevels.In the sequential tunneling regime,the differential conductance exhibits (2S + 1) possible peaks,corresponding to resonance tunneling via (2S + 1) sublevels.At low temperature,Kondo physics dominates transport and (2S + 1) Kondo peaks occur in the local density of states and conductance.These peaks originate from the spin-singlet state formed by the holes in the leads and on the dot via higher-order processes and are related to the parallel and antiparallel spin pair states.
Hayashi, Yuya; Takai, Shun; Matsumura, Takeshi; Tanida, Hiroshi; Sera, Masafumi; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Ochiai, Akira
2016-03-01
We have measured the electrical resistivity of cerium monochalcogenides, CeS, CeSe, and CeTe, under high pressures of up to 8 GPa. The pressure dependences of the antiferromagnetic ordering temperature TN, crystal field splitting, and the ln T anomaly of the Kondo effect have been studied to cover the entire region from the magnetic ordering regime at low pressure to the Fermi liquid regime at high pressure. TN initially increases with increasing pressure, and starts to decrease at high pressure as expected from Doniach’s diagram. Simultaneously, the ln T behavior in the resistivity is enhanced, indicating the enhancement of the Kondo effect by pressure. It is also characteristic of CeXc that the crystal field splitting rapidly decreases at a common rate of -12.2 K/GPa. This leads to the increase in the degeneracy of the f state and the further enhancement of the Kondo effect. It is shown that the pressure-dependent degeneracy of the f state is a key factor for understanding the pressure dependence of TN, the Kondo effect, magnetoresistance, and the peak structure in the temperature dependence of resistivity.
Von Smekal, L; Sternbeck, A; Williams, A G
2007-01-01
We propose a modified lattice Landau gauge based on stereographically projecting the link variables on the circle S^1 -> R for compact U(1) or the 3-sphere S^3 -> R^3 for SU(2) before imposing the Landau gauge condition. This can reduce the number of Gribov copies exponentially and solves the Gribov problem in compact U(1) where it is a lattice artifact. Applied to the maximal Abelian subgroup this might be just enough to avoid the perfect cancellation amongst the Gribov copies in a lattice BRST formulation for SU(N), and thus to avoid the Neuberger 0/0 problem. The continuum limit of the Landau gauge remains unchanged.
Jammed lattice sphere packings.
Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore
2013-12-01
We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a model for the jamming and glass transitions that enables exploration of much higher dimensions than are usually accessible.
Jammed lattice sphere packings
Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore
2013-12-01
We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a model for the jamming and glass transitions that enables exploration of much higher dimensions than are usually accessible.
Xiong, Yong-Chen; Wang, Wei-Zhong; Luo, Shi-Jun; Yang, Jun-Tao; Huang, Hai-Ming
2017-03-01
By means of the numerical renormalization group (NRG) technique, we study the low temperature transport property and the phase transition for a triangular triple quantum dot system, including two centered dots (dot 1 and 2) and one side dot (dot 3). We focus on the effect of interdot repulsion V between two centered dots in a wide range of the interdot hopping tij (i,j = 1,2,3). When the hoppings between the centered dot and the side dot are symmetric, i.e., t13 = t23, and that between two centered dots t12 is small, two centered dots form a spin triplet when V is absent, and a totally screened spin-1 Kondo effect is observed. In this case, one has a spin 1 that is partially screened by the leads as in the usual spin-1 Kondo model, and the remaining spin 1/2 degree of freedom forms a singlet with the side dot. As V is large enough, one of the centered dots is singly occupied, while the other one is empty. The spin-1/2 Kondo effect is found when t13 is small. For large t12, two centered dots form a spin singlet when V = 0, leading to zero conductance. As V is large enough, the spin-1/2 Kondo effect is recovered in the case of small t13. For asymmetric t13≠t23 and small t12, a crossover is found as V increases in comparison with a first order quantum phase transition for the symmetric case. In the regime of large V, the spin-1/2 Kondo effect could also be found when both t13 and t23 are small. We demonstrate the present model is similar to the side-coupled double dot system in some appropriate regimes, and it appears as a possible realization of side-controllable molecular electronics and spintronics devices.
Lipstein, Arthur E
2014-01-01
We formulate the theory of a 2-form gauge field on a Euclidean spacetime lattice. In this approach, the fundamental degrees of freedom live on the faces of the lattice, and the action can be constructed from the sum over Wilson surfaces associated with each fundamental cube of the lattice. If we take the gauge group to be $U(1)$, the theory reduces to the well-known abelian gerbe theory in the continuum limit. We also propose a very simple and natural non-abelian generalization with gauge group $U(N) \\times U(N)$, which gives rise to $U(N)$ Yang-Mills theory upon dimensional reduction. Formulating the theory on a lattice has several other advantages. In particular, it is possible to compute many observables, such as the expectation value of Wilson surfaces, analytically at strong coupling and numerically for any value of the coupling.
Root lattices and quasicrystals
Baake, M.; Joseph, D.; Kramer, P.; Schlottmann, M.
1990-10-01
It is shown that root lattices and their reciprocals might serve as the right pool for the construction of quasicrystalline structure models. All noncrystallographic symmetries observed so far are covered in minimal embedding with maximal symmetry.
Energy Technology Data Exchange (ETDEWEB)
ORGINOS,K.
2003-01-07
I review the current status of hadronic structure computations on the lattice. I describe the basic lattice techniques and difficulties and present some of the latest lattice results; in particular recent results of the RBC group using domain wall fermions are also discussed. In conclusion, lattice computations can play an important role in understanding the hadronic structure and the fundamental properties of Quantum Chromodynamics (QCD). Although some difficulties still exist, several significant steps have been made. Advances in computer technology are expected to play a significant role in pushing these computations closer to the chiral limit and in including dynamical fermions. RBC has already begun preliminary dynamical domain wall fermion computations [49] which we expect to be pushed forward with the arrival of QCD0C. In the near future, we also expect to complete the non-perturbative renormalization of the relevant derivative operators in quenched QCD.
Superalloy Lattice Block Structures
Nathal, M. V.; Whittenberger, J. D.; Hebsur, M. G.; Kantzos, P. T.; Krause, D. L.
2004-01-01
Initial investigations of investment cast superalloy lattice block suggest that this technology will yield a low cost approach to utilize the high temperature strength and environmental resistance of superalloys in lightweight, damage tolerant structural configurations. Work to date has demonstrated that relatively large superalloy lattice block panels can be successfully investment cast from both IN-718 and Mar-M247. These castings exhibited mechanical properties consistent with the strength of the same superalloys measured from more conventional castings. The lattice block structure also accommodates significant deformation without failure, and is defect tolerant in fatigue. The potential of lattice block structures opens new opportunities for the use of superalloys in future generations of aircraft applications that demand strength and environmental resistance at elevated temperatures along with low weight.
Vector Lattice Vortex Solitons
Institute of Scientific and Technical Information of China (English)
WANG Jian-Dong; YE Fang-Wei; DONG Liang-Wei; LI Yong-Ping
2005-01-01
@@ Two-dimensional vector vortex solitons in harmonic optical lattices are investigated. The stability properties of such solitons are closely connected to the lattice depth Vo. For small Vo, vector vortex solitons with the total zero-angular momentum are more stable than those with the total nonzero-angular momentum, while for large Vo, this case is inversed. If Vo is large enough, both the types of such solitons are stable.
Pica, C; Lucini, B; Patella, A; Rago, A
2009-01-01
Technicolor theories provide an elegant mechanism for dynamical electroweak symmetry breaking. We will discuss the use of lattice simulations to study the strongly-interacting dynamics of some of the candidate theories, with matter fields in representations other than the fundamental. To be viable candidates for phenomenology, such theories need to be different from a scaled-up version of QCD, which were ruled out by LEP precision measurements, and represent a challenge for modern lattice computations.
Automated Lattice Perturbation Theory
Energy Technology Data Exchange (ETDEWEB)
Monahan, Christopher
2014-11-01
I review recent developments in automated lattice perturbation theory. Starting with an overview of lattice perturbation theory, I focus on the three automation packages currently "on the market": HiPPy/HPsrc, Pastor and PhySyCAl. I highlight some recent applications of these methods, particularly in B physics. In the final section I briefly discuss the related, but distinct, approach of numerical stochastic perturbation theory.
Kiefel, Martin; Jampani, Varun; Gehler, Peter V.
2014-01-01
This paper presents a convolutional layer that is able to process sparse input features. As an example, for image recognition problems this allows an efficient filtering of signals that do not lie on a dense grid (like pixel position), but of more general features (such as color values). The presented algorithm makes use of the permutohedral lattice data structure. The permutohedral lattice was introduced to efficiently implement a bilateral filter, a commonly used image processing operation....
Solitons in spiraling Vogel lattices
Kartashov, Yaroslav V; Torner, Lluis
2012-01-01
We address light propagation in Vogel optical lattices and show that such lattices support a variety of stable soliton solutions in both self-focusing and self-defocusing media, whose propagation constants belong to domains resembling gaps in the spectrum of a truly periodic lattice. The azimuthally-rich structure of Vogel lattices allows generation of spiraling soliton motion.
Chen, Jianxin; Zhuo, Shuangmu; Luo, Tianshu; Liu, Dingzhong; Zhao, Jingjun
2008-08-01
Collagen and elastin are the most important proteins of the connective tissues in higher vertebrates. In this paper, we present a combined nonlinear optical imaging technique of second-harmonic generation and two-photon excited fluorescence to simultaneously observe the collagen and elastic fiber of dermis in a freshly excised human skin and rabbit aorta using a two-channel synchronized detection method. The obtained two-channel overlay image in the backward direction can clearly distinguish the morphological structure and distribution of collagen and elastic fibers. Tissue spectrum further confirms the obtained structural information. These results suggest that the combined nonlinear optical imaging technique coupled with two-channel synchronized detection method can be an effective tool for detecting collage and elastic fibers without any invasive tissue procedure of slicing, embedding, fixation and staining when two structural proteins are simultaneously present in the biological tissue.
Gate-controlled spin splitting in quantum dots with ferromagnetic leads in the Kondo regime
Martinek, J.; Sindel, M.; Borda, L.; Barnaś, J.; Bulla, R.; König, J.; Schön, G.; Maekawa, S.; von Delft, J.
2005-09-01
The effect of a gate voltage ( Vg ) on the spin splitting of an electronic level in a quantum dot (QD) attached to ferromagnetic leads is studied in the Kondo regime using a generalized numerical renormalization group technique. We find that the Vg dependence of the QD level spin splitting strongly depends on the shape of the density of states (DOS). For one class of DOS shapes there is nearly no Vg dependence; for another, Vg can be used to control the magnitude and sign of the spin splitting, which can be interpreted as a local exchange magnetic field. We find that the spin splitting acquires a new type of logarithmic divergence. We give an analytical explanation for our numerical results and explain how they arise due to spin-dependent charge fluctuations.
Two-dimensional Fermi surfaces in Kondo insulator SmB₆.
Li, G; Xiang, Z; Yu, F; Asaba, T; Lawson, B; Cai, P; Tinsman, C; Berkley, A; Wolgast, S; Eo, Y S; Kim, Dae-Jeong; Kurdak, C; Allen, J W; Sun, K; Chen, X H; Wang, Y Y; Fisk, Z; Li, Lu
2014-12-05
In the Kondo insulator samarium hexaboride (SmB6), strong correlation and band hybridization lead to an insulating gap and a diverging resistance at low temperature. The resistance divergence ends at about 3 kelvin, a behavior that may arise from surface conductance. We used torque magnetometry to resolve the Fermi surface topology in this material. The observed oscillation patterns reveal two Fermi surfaces on the (100) surface plane and one Fermi surface on the (101) surface plane. The measured Fermi surface cross sections scale as the inverse cosine function of the magnetic field tilt angles, which demonstrates the two-dimensional nature of the conducting electronic states of SmB6. Copyright © 2014, American Association for the Advancement of Science.
Kondo effect from a Lorentz-violating domain wall description of superconductivity
Bazeia, D; Mota-Silva, J C
2016-01-01
We extend recent results on domain wall description of superconductivity in an Abelian Higgs model by introducing a particular Lorentz-violating term. The temperature of the system is interpreted through the fact that the soliton following accelerating orbits is a Rindler observer experiencing a thermal bath. We show that this term can be associated with the {\\sl Kondo effect}, that is, the Lorentz-violating parameter is closely related to the concentration of magnetic impurities living on a superconducting domain wall. We also found that the critical temperature decreasing with the impurity concentration as a non-single valued function, for the case $T_K
Low-temperature transport in ac-driven quantum dots in the Kondo regime
Energy Technology Data Exchange (ETDEWEB)
Lopez, Rosa; Aguado, Ramon; Platero, Gloria; Tejedor, Carlos
2001-08-15
We present a fully nonequilibrium calculation of the low-temperature transport properties of a quantum dot in the Kondo regime when an ac potential is applied to the gate. We solve a time-dependent Anderson model with finite on-site Coulomb interaction. The interaction self-energy is calculated up to second order in perturbation theory in the on-site interaction, in the context of the Keldysh nonequilibrium technique, and the effect of the ac voltage is taken into account exactly for all ranges of ac frequencies and ac intensities. The obtained linear conductance and time-averaged density of states of the quantum dot evolve in a nontrivial way as a function of the ac frequency and ac intensity of the harmonic modulation.
Proposed Rabi-Kondo correlated state in a laser-driven semiconductor quantum dot.
Sbierski, B; Hanl, M; Weichselbaum, A; Türeci, H E; Goldstein, M; Glazman, L I; von Delft, J; Imamoğlu, A
2013-10-11
Spin exchange between a single-electron charged quantum dot and itinerant electrons leads to an emergence of Kondo correlations. When the quantum dot is driven resonantly by weak laser light, the resulting emission spectrum allows for a direct probe of these correlations. In the opposite limit of vanishing exchange interaction and strong laser drive, the quantum dot exhibits coherent oscillations between the single-spin and optically excited states. Here, we show that the interplay between strong exchange and nonperturbative laser coupling leads to the formation of a new nonequilibrium quantum-correlated state, characterized by the emergence of a laser-induced secondary spin screening cloud, and examine the implications for the emission spectrum.
Proximity effect induced by Kondo interaction in a network composed of YBCO and spin density wave
Maity, S.; Ghosh, Ajay Kumar
2015-10-01
The possibility of the proximity effect mediated by Kondo interaction in YBCO embedded in system of diluted magnetic spin ordering has been studied. An YBCO sample is selected in which both metal to insulator transition and superconducting state exist in the different ranges of temperature. The intergranular network of the bulk Y-123 has been modified by the inclusion of YMnO3 which has a well defined magnetic structure depending on temperature. The current-voltage measurements have been carried out in pure Y-123 at several temperatures. At the same set of temperatures the current-voltage curves in presence of YMnO3 have been studied. The role of the diluted spin magnetic ordering in tuning proximity effect and conduction property in binary systems is associated with reduced coherence length in the normal region.
Photoemission study of the ferromagnetic Kondo system CeRh3B2
Fujimori, A.; Takahashi, T.; Okabe, A.; Kasaya, M.; Kasuya, T.
1990-04-01
We have studied the electronic structure of CeRh3B2, which has an anomalously high ferromagnetic ordering temperature, by photoemission and Auger-electron spectroscopy. The Ce 4f occupancy nf~=0.85 evaluated from the Ce 3d core-level photoemission spectrum indicates a moderately strong valence fluctuation in the Kondo regime. Rh d-derived valence-band photoemission spectra are found to be in good agreement with the results of band-structure calculations when a strong energy dependence of the hole lifetime is taken into account. This observation and the deviation of the Rh M4,5VV Auger spectrum from the self-convolution of the Rh d partial density of states provide evidence for electron correlation within the Rh d band of order of U=1-2 eV. We discuss a possible effect of the latter electron correlation on the ferromagnetic instability of this compound.
From tunneling to contact in a magnetic atom: The non-equilibrium Kondo effect
Choi, Deung-Jang; Abufager, Paula; Limot, Laurent; Lorente, Nicolás
2017-03-01
A low-temperature scanning tunneling microscope was employed to study the differential conductance in an atomic junction formed by an adsorbed Co atom on a Cu(100) surface and a copper-covered tip. A zero-bias anomaly (ZBA) reveals spin scattering off the Co atom, which is assigned to a Kondo effect. The ZBA exhibits a characteristic asymmetric lineshape when electrons tunnel between tip and sample, while upon the tip-Co contact it symmetrizes and broadens. Through density functional theory calculations and the non-equilibrium non-crossing approximation, we show that the lineshape broadening is mainly a consequence of the additional coupling to the tip, while non-equilibrium effects only modify the large-bias tails of the ZBA.
Low energy properties of the Kondo chain in the RKKY regime
Schimmel, D. H.; Tsvelik, A. M.; Yevtushenko, O. M.
2016-05-01
We study the Kondo chain in the regime of high spin concentration where the low energy physics is dominated by the Ruderman-Kittel-Kasuya-Yosida interaction. As has been recently shown (Tsvelik and Yevtushenko 2015 Phys. Rev. Lett. 115 216402), this model has two phases with drastically different transport properties depending on the anisotropy of the exchange interaction. In particular, the helical symmetry of the fermions is spontaneously broken when the anisotropy is of the easy plane type. This leads to a parametrical suppression of the localization effects. In the present paper we substantially extend the previous theory, in particular, by analyzing a competition of forward- and backward- scattering, including into the theory short range electron interactions and calculating spin correlation functions. We discuss applicability of our theory and possible experiments which could support the theoretical findings.
Effects of van Hove Singularities on Transport of Quantum Dot Systems in Kondo Regime
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
In the present paper, we study the effect of van Hove singularities of conduction electron on the transport of a single quantum dot system in the Kondo regime. By using both the equation-of-motion and the noncrossing approximation techniques, we show that the corrections caused by these singularities are actually minor. It can be explained by observing that the singularities in the equations, which determine the electronic DOS on the dot, are integrable. Furthermore, we find that, although each line width function is divergent at van Hove singular points, the total divergence is canceled out in the final formula to calculate the current through the system. Therefore, as far as the qualitative properties of the system is concerned, these singularities can be ignored and the wide-band approximation can be safely used in calculation.
Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets
Ray, Rajyavardhan; Kumar, Sanjeev
2017-01-01
We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications. PMID:28176869
Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets
Ray, Rajyavardhan; Kumar, Sanjeev
2017-02-01
We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications.
4f heavy fermion photoelectron spectra do not exhibit the Kondo scale
Energy Technology Data Exchange (ETDEWEB)
Arko, A.J.; Joyce, J.J.; Andrews, A.B.; Blyth, R.I.R.; Bartlett, R.J.; Fisk, Z. [Los Alamos National Lab., NM (United States); Canfield, P.C.; Olson, C.G.; Benning, P.J. [Iowa State Univ., Ames, IA (United States); Poirier, D.M.; Weaver, J.H. [Univ. of Minnesota, Minneapolis, MN (United States); Riseborough, P.S. [Polytechnic Univ., Brooklyn, NY (United States)
1994-02-01
It has been the authors contention for some time that the Single Impurity Anderson Model (SIAM), as extended by Gunnarsson and Schonhammer (GS), or the non-crossing approximation (NCA), does not correctly describe the 4f photoelectron spectra of heavy fermions. Recently, they have concentrated on Yb heavy fermions since in these materials the Kondo resonance (KR) is fully occupied and thus accessible via photoemission. In particular, they have repeatedly pointed out that the width, position, spectral weight, lineshape, and temperature dependence of the features assumed to be the KR and its sidebands, are nearly independent of the Kondo temperature, T{sub K}, while at the same time bearing a striking resemblance to the simple 4f core level spectra of pure Yb metal, or of Lu in isostructural Lu compounds. It is important to resolve these issues in view of the fundamental nature of the problem. Here, the authors chose to test the bulk vs. surface hypothesis by performing measurements on YbCu{sub 2}Si{sub 2} and YbAl{sub 3} single crystals at hv {approx} 120 eV (UPS) and hv {approx} 1,500 eV(XPS) to see if the n{sub f}, hole occupancy, values increase markedly at XPS energies as the electron escape depth increases by about a factor of 3--5. Measurements were performed at both 300K and 20K using single crystals cleaved in-situ, with photoelectrons collected in normal emission for maximum bulk sensitivity. UPS measurements were performed at NSLS and the University of Wisconsin SRC, while XPS measurements were done at the University of Minnesota. The UPS, ultraviolet photoelectron spectra, and the L{sub III} edge x-ray absorption and photoemission measurements are in fundamental disagreement.
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.
A Bijection between Lattice-Valued Filters and Lattice-Valued Congruences in Residuated Lattices
Directory of Open Access Journals (Sweden)
Wei Wei
2013-01-01
Full Text Available The aim of this paper is to study relations between lattice-valued filters and lattice-valued congruences in residuated lattices. We introduce a new definition of congruences which just depends on the meet ∧ and the residuum →. Then it is shown that each of these congruences is automatically a universal-algebra-congruence. Also, lattice-valued filters and lattice-valued congruences are studied, and it is shown that there is a one-to-one correspondence between the set of all (lattice-valued filters and the set of all (lattice-valued congruences.
Energy Technology Data Exchange (ETDEWEB)
NONE
1998-12-01
Using VLF frequencies, transmitted by the Navy`s network, for airborne remote sensing of the earth`s electrical, magnetic characteristics was first considered by the United States Geological Survey (USGS) around the mid 1970s. The first VLF system was designed and developed by the USGS for installation and operation on a single engine, fixed wing aircraft used by the Branch of Geophysics for geophysical surveying. The system consisted of five channels. Two E-field channels with sensors consisting of a fixed vertical loaded dipole antenna with pre-amp mounted on top of the fuselage and a gyro stabilized horizontal loaded dipole antenna with pre-amp mounted on a tail boom. The three channel magnetic sensor consisted of three orthogonal coils mounted on the same gyro stabilized platform as the horizontal E-field antenna. The main features of the VLF receiver were: narrow band-width frequency selection using crystal filters, phase shifters for zeroing out system phase variances, phase-lock loops for generating real and quadrature gates, and synchronous detectors for generating real and quadrature outputs. In the mid 1990s the Branch of Geophysics designed and developed a two-channel E-field ground portable VLF system. The system was built using state-of-the-art circuit components and new concepts in circuit architecture. Small size, light weight, low power, durability, and reliability were key considerations in the design of the instrument. The primary purpose of the instrument was for collecting VLF data during ground surveys over small grid areas. Later the system was modified for installation on a Unmanned Airborne Vehicle (UAV). A series of three field trips were made to Easton, Maryland for testing and evaluating the system performance.
Missing channels in two-colour microarray experiments: Combining single-channel and two-channel data
Directory of Open Access Journals (Sweden)
Burtt Glyn J
2007-01-01
Full Text Available Abstract Background There are mechanisms, notably ozone degradation, that can damage a single channel of two-channel microarray experiments. Resulting analyses therefore often choose between the unacceptable inclusion of poor quality data or the unpalatable exclusion of some (possibly a lot of good quality data along with the bad. Two such approaches would be a single channel analysis using some of the data from all of the arrays, and an analysis of all of the data, but only from unaffected arrays. In this paper we examine a 'combined' approach to the analysis of such affected experiments that uses all of the unaffected data. Results A simulation experiment shows that while a single channel analysis performs relatively well when the majority of arrays are affected, and excluding affected arrays performs relatively well when few arrays are affected (as would be expected in both cases, the combined approach out-performs both. There are benefits to actively estimating the key-parameter of the approach, but whether these compensate for the increased computational cost and complexity over just setting that parameter to take a fixed value is not clear. Inclusion of ozone-affected data results in poor performance, with a clear spatial effect in the damage being apparent. Conclusion There is no need to exclude unaffected data in order to remove those which are damaged. The combined approach discussed here is shown to out-perform more usual approaches, although it seems that if the damage is limited to very few arrays, or extends to very nearly all, then the benefits will be limited. In other circumstances though, large improvements in performance can be achieved by adopting such an approach.
Directory of Open Access Journals (Sweden)
G. V. Sotnikov
2011-03-01
Full Text Available Here we show a possibility of applying the ramped drive bunch train (RBT technique to a two-channel coaxial dielectric wakefield accelerator (CDWA. For numerical research we study a 28 GHz structure with two nested alumina cylindrical shells having these diameters: outer shell, OD=28.1 mm, ID=27 mm; inner shell, OD=6.35 mm, ID=4.0 mm. The structure is to be excited by a train of four annular bunches having energy 14 MeV and axial rms length 1 mm; the total charge of bunches is 200 nC. In the case of equally charged drive bunches, spaced apart by the principal wakefield wavelength 10.67 mm, we obtained transformer ratio T=3.4. If the bunch charge is increasing as the ratio 1∶3∶5∶7 and the bunches are spaced by one and one-half wavelengths, we obtained T=3.8. We found that if the charge ratios are 1.0∶2.4∶3.5∶5.0 and the spaces between the bunches are 2.5, 2.5, and 4.5 wakefield periods, then T increases strongly, T∼20. The RBT also can be used successfully in a high gradient THz CDWA structure. A particle-in-cell simulation shows that the four drive bunches can move without appreciable distortion.
Knuth, Kevin H.
2009-12-01
Previous derivations of the sum and product rules of probability theory relied on the algebraic properties of Boolean logic. Here they are derived within a more general framework based on lattice theory. The result is a new foundation of probability theory that encompasses and generalizes both the Cox and Kolmogorov formulations. In this picture probability is a bi-valuation defined on a lattice of statements that quantifies the degree to which one statement implies another. The sum rule is a constraint equation that ensures that valuations are assigned so as to not violate associativity of the lattice join and meet. The product rule is much more interesting in that there are actually two product rules: one is a constraint equation arises from associativity of the direct products of lattices, and the other a constraint equation derived from associativity of changes of context. The generality of this formalism enables one to derive the traditionally assumed condition of additivity in measure theory, as well introduce a general notion of product. To illustrate the generic utility of this novel lattice-theoretic foundation of measure, the sum and product rules are applied to number theory. Further application of these concepts to understand the foundation of quantum mechanics is described in a joint paper in this proceedings.
Lattice Boltzmann Stokesian dynamics.
Ding, E J
2015-11-01
Lattice Boltzmann Stokesian dynamics (LBSD) is presented for simulation of particle suspension in Stokes flows. This method is developed from Stokesian dynamics (SD) with resistance and mobility matrices calculated using the time-independent lattice Boltzmann algorithm (TILBA). TILBA is distinguished from the traditional lattice Boltzmann method (LBM) in that a background matrix is generated prior to the calculation. The background matrix, once generated, can be reused for calculations for different scenarios, thus the computational cost for each such subsequent calculation is significantly reduced. The LBSD inherits the merits of the SD where both near- and far-field interactions are considered. It also inherits the merits of the LBM that the computational cost is almost independent of the particle shape.
Weisz, Peter; Majumdar, Pushan
2012-03-01
Lattice gauge theory is a formulation of quantum field theory with gauge symmetries on a space-time lattice. This formulation is particularly suitable for describing hadronic phenomena. In this article we review the present status of lattice QCD. We outline some of the computational methods, discuss some phenomenological applications and a variety of non-perturbative topics. The list of references is severely incomplete, the ones we have included are text books or reviews and a few subjectively selected papers. Kronfeld and Quigg (2010) supply a reasonably comprehensive set of QCD references. We apologize for the fact that have not covered many important topics such as QCD at finite density and heavy quark effective theory adequately, and mention some of them only in the last section "In Brief". These topics should be considered in further Scholarpedia articles.
Improved Lattice Radial Quantization
Brower, Richard C; Fleming, George T
2014-01-01
Lattice radial quantization was proposed in a recent paper by Brower, Fleming and Neuberger[1] as a nonperturbative method especially suited to numerically solve Euclidean conformal field theories. The lessons learned from the lattice radial quantization of the 3D Ising model on a longitudinal cylinder with 2D Icosahedral cross-section suggested the need for an improved discretization. We consider here the use of the Finite Element Methods(FEM) to descretize the universally-equivalent $\\phi^4$ Lagrangian on $\\mathbb R \\times \\mathbb S^2$. It is argued that this lattice regularization will approach the exact conformal theory at the Wilson-Fisher fixed point in the continuum. Numerical tests are underway to support this conjecture.
Graphene antidot lattice waveguides
DEFF Research Database (Denmark)
Pedersen, Jesper Goor; Gunst, Tue; Markussen, Troels
2012-01-01
We introduce graphene antidot lattice waveguides: nanostructured graphene where a region of pristine graphene is sandwiched between regions of graphene antidot lattices. The band gaps in the surrounding antidot lattices enable localized states to emerge in the central waveguide region. We model...... the waveguides via a position-dependent mass term in the Dirac approximation of graphene and arrive at analytical results for the dispersion relation and spinor eigenstates of the localized waveguide modes. To include atomistic details we also use a tight-binding model, which is in excellent agreement...... with the analytical results. The waveguides resemble graphene nanoribbons, but without the particular properties of ribbons that emerge due to the details of the edge. We show that electrons can be guided through kinks without additional resistance and that transport through the waveguides is robust against...
Digital lattice gauge theories
Zohar, Erez; Reznik, Benni; Cirac, J Ignacio
2016-01-01
We propose a general scheme for a digital construction of lattice gauge theories with dynamical fermions. In this method, the four-body interactions arising in models with $2+1$ dimensions and higher, are obtained stroboscopically, through a sequence of two-body interactions with ancillary degrees of freedom. This yields stronger interactions than the ones obtained through pertubative methods, as typically done in previous proposals, and removes an important bottleneck in the road towards experimental realizations. The scheme applies to generic gauge theories with Lie or finite symmetry groups, both Abelian and non-Abelian. As a concrete example, we present the construction of a digital quantum simulator for a $\\mathbb{Z}_{3}$ lattice gauge theory with dynamical fermionic matter in $2+1$ dimensions, using ultracold atoms in optical lattices, involving three atomic species, representing the matter, gauge and auxiliary degrees of freedom, that are separated in three different layers. By moving the ancilla atoms...
Oates, Chris
2012-06-01
Since they were first proposed in 2003 [1], optical lattice clocks have become one of the leading technologies for the next generation of atomic clocks, which will be used for advanced timing applications and in tests of fundamental physics [2]. These clocks are based on stabilized lasers whose frequency is ultimately referenced to an ultra-narrow neutral atom transition (natural linewidths magic'' value so as to yield a vanishing net AC Stark shift for the clock transition. As a result lattice clocks have demonstrated the capability of generating high stability clock signals with small absolute uncertainties (˜ 1 part in 10^16). In this presentation I will first give an overview of the field, which now includes three different atomic species. I will then use experiments with Yb performed in our laboratory to illustrate the key features of a lattice clock. Our research has included the development of state-of-the-art optical cavities enabling ultra-high-resolution optical spectroscopy (1 Hz linewidth). Together with the large atom number in the optical lattice, we are able to achieve very low clock instability (< 0.3 Hz in 1 s) [3]. Furthermore, I will show results from some of our recent investigations of key shifts for the Yb lattice clock, including high precision measurements of ultracold atom-atom interactions in the lattice and the dc Stark effect for the Yb clock transition (necessary for the evaluation of blackbody radiation shifts). [4pt] [1] H. Katori, M. Takamoto, V. G. Pal'chikov, and V. D. Ovsiannikov, Phys. Rev. Lett. 91, 173005 (2003). [0pt] [2] Andrei Derevianko and Hidetoshi Katori, Rev. Mod. Phys. 83, 331 (2011). [0pt] [3] Y. Y. Jiang, A. D. Ludlow, N. D. Lemke, R. W. Fox, J. A. Sherman, L.-S. Ma, and C. W. Oates, Nature Photonics 5, 158 (2011).
Directory of Open Access Journals (Sweden)
Qian Zhou
2016-01-01
Full Text Available OBJECTIVE: The aim of this study was to determine the efficacy of 252Californium neutron intracavitary brachytherapy using a two-channel Y applicator combined with external beam radiotherapy for the treatment of endometrial cancer. METHODS: Thirty-one patients with stage I-III endometrial cancer were recruited for this study. The stage I patients received only 252Californium neutron intracavitary brachytherapy with a two-channel applicator. The stage II and III patients received both 252Californium neutron intracavitary brachytherapy using a two-channel applicator and parallel-opposed whole pelvic radiotherapy. RESULTS: The five-year local control rate was 80.6% (25/31, the overall survival rate was 51.6% (16/31, and the disease-free survival rate was 54.8% (17/31. The incidence of serious late complications was 12.9% (4/31. CONCLUSIONS: 252Californium neutron intracavitary brachytherapy using a two-channel applicator combined with external beam radiotherapy was effective for treating endometrial cancer and the incidence of serious late complications related to this combination was within an acceptable range.
Zhou, Qian; Tang, Cheng; Zhao, Ke-Wei; Xiong, Yan-Li; Chen, Shu; Xu, Wen-Jing; Lei, Xin
2016-01-01
The aim of this study was to determine the efficacy of 252Californium neutron intracavitary brachytherapy using a two-channel Y applicator combined with external beam radiotherapy for the treatment of endometrial cancer. Thirty-one patients with stage I-III endometrial cancer were recruited for this study. The stage I patients received only 252Californium neutron intracavitary brachytherapy with a two-channel applicator. The stage II and III patients received both 252Californium neutron intracavitary brachytherapy using a two-channel applicator and parallel-opposed whole pelvic radiotherapy. The five-year local control rate was 80.6% (25/31), the overall survival rate was 51.6% (16/31), and the disease-free survival rate was 54.8% (17/31). The incidence of serious late complications was 12.9% (4/31). 252Californium neutron intracavitary brachytherapy using a two-channel applicator combined with external beam radiotherapy was effective for treating endometrial cancer and the incidence of serious late complications related to this combination was within an acceptable range.
Energy Technology Data Exchange (ETDEWEB)
Catterall, Simon; Kaplan, David B.; Unsal, Mithat
2009-03-31
We provide an introduction to recent lattice formulations of supersymmetric theories which are invariant under one or more real supersymmetries at nonzero lattice spacing. These include the especially interesting case of N = 4 SYM in four dimensions. We discuss approaches based both on twisted supersymmetry and orbifold-deconstruction techniques and show their equivalence in the case of gauge theories. The presence of an exact supersymmetry reduces and in some cases eliminates the need for fine tuning to achieve a continuum limit invariant under the full supersymmetry of the target theory. We discuss open problems.
Grabisch, Michel
2008-01-01
We extend the notion of belief function to the case where the underlying structure is no more the Boolean lattice of subsets of some universal set, but any lattice, which we will endow with a minimal set of properties according to our needs. We show that all classical constructions and definitions (e.g., mass allocation, commonality function, plausibility functions, necessity measures with nested focal elements, possibility distributions, Dempster rule of combination, decomposition w.r.t. simple support functions, etc.) remain valid in this general setting. Moreover, our proof of decomposition of belief functions into simple support functions is much simpler and general than the original one by Shafer.
Temperature Dependence of the Kondo Resonance and Its Satellites in CeCu{sub 2}Si{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Reinert, F.; Ehm, D.; Schmidt, S.; Nicolay, G.; Huefner, S.; Kroha, J.; Trovarelli, O.; Geibel, C.
2001-09-03
We present high-resolution photoemission spectroscopy studies on the Kondo resonance of the strongly correlated Ce system CeCu{sub 2}Si {sub 2} . By exploiting the thermal broadening of the Fermi edge we analyze position, spectral weight, and temperature dependence of the low-energy 4f spectral features, whose major weight lies above the Fermi level E{sub F} . We also present theoretical predictions based on the single-impurity Anderson model using an extended noncrossing approximation, including all spin-orbit and crystal field splittings of the 4f states. The excellent agreement between theory and experiment provides strong evidence that the spectral properties of CeCu{sub 2}Si {sub 2} can be described by single-impurity Kondo physics down to T{approx}5 K .
Energy Technology Data Exchange (ETDEWEB)
Eckle, H.-P.; Johannesson, H.; Stafford, C. A.
2001-07-02
We study the persistent currents induced by both the Aharonov-Bohm and Aharonov-Casher effects in a one-dimensional mesoscopic ring coupled to a sidebranch quantum dot at Kondo resonance. For privileged values of the Aharonov-Bohm-Casher fluxes, the problem can be mapped onto an integrable model, exactly solvable by a Bethe ansatz. In the case of a pure magnetic Aharonov-Bohm flux, we find that the presence of the quantum dot has no effect on the persistent current. In contrast, the Kondo resonance interferes with the spin-dependent Aharonov-Casher effect to induce a current which, in the strong-coupling limit, is independent of the number of electrons in the ring.
Eckle, H P; Johannesson, H; Stafford, C A
2001-07-02
We study the persistent currents induced by both the Aharonov-Bohm and Aharonov-Casher effects in a one-dimensional mesoscopic ring coupled to a sidebranch quantum dot at Kondo resonance. For privileged values of the Aharonov-Bohm-Casher fluxes, the problem can be mapped onto an integrable model, exactly solvable by a Bethe ansatz. In the case of a pure magnetic Aharonov-Bohm flux, we find that the presence of the quantum dot has no effect on the persistent current. In contrast, the Kondo resonance interferes with the spin-dependent Aharonov-Casher effect to induce a current which, in the strong-coupling limit, is independent of the number of electrons in the ring.
Aksu, H.; Goker, A.
2017-03-01
We invoke the nonequilibrium self-consistent GW method within the Anderson impurity model to investigate the dynamical effects occurring in a nanojunction comprised of two coupled molecules. Contrary to the previous single impurity model calculations based on the GW approximation, we observe that the density of states manages to capture both the Kondo resonance and the Breit-Wigner resonances associated with the HOMO and LUMO levels of the molecule. Moreover, the prominence of the Kondo resonance grows dramatically upon switching from the intermediate to the weak coupling regime involving large U / Γ values. The conductance is calculated as a function of the HOMO level and the applied bias across the molecular nanojunction. Calculated conductance curves deviate from the monotonic decay behaviour as a function of the bias when the half-filling condition is not met. The importance of the effect of the molecule-molecule coupling for the electron transport phenomena is also investigated.
Giant Kondo Resonance of Parallel-Coupled Double Quantum Dots Embedded in an A-B Ring
Institute of Scientific and Technical Information of China (English)
CHEN Xiong-Wen; HE Da-Jiang; SONG Ke-Hui; WU Shao-Quan
2006-01-01
We theoretically study the properties of the ground state of the parallel-coupled double quantum dots embedded in a mesoscopic ring in the Kondo regime by means of the two-impurity Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. We find that in this system, the persistent current depends sensitively on both the parity of this system and the size of the ring. In the strong coupling regime, the giant sharp current peak appears, at the same time, the parity dependence of the persistent current disappears. These imply that in the strong coupling regime, there exists giant Kondo resonance and the two dots can be coupled coherently. Thus this system might be a candidate for future device applications.
Directory of Open Access Journals (Sweden)
Futa Yuichi
2016-03-01
Full Text Available In this article, we formalize the definition of lattice of ℤ-module and its properties in the Mizar system [5].We formally prove that scalar products in lattices are bilinear forms over the field of real numbers ℝ. We also formalize the definitions of positive definite and integral lattices and their properties. Lattice of ℤ-module is necessary for lattice problems, LLL (Lenstra, Lenstra and Lovász base reduction algorithm [14], and cryptographic systems with lattices [15] and coding theory [9].
An Algorithm on Generating Lattice Based on Layered Concept Lattice
Directory of Open Access Journals (Sweden)
Zhang Chang-sheng
2013-08-01
Full Text Available Concept lattice is an effective tool for data analysis and rule extraction, a bottleneck factor on impacting the applications of concept lattice is how to generate lattice efficiently. In this paper, an algorithm LCLG on generating lattice in batch processing based on layered concept lattice is developed, this algorithm is based on layered concept lattice, the lattice is generated downward layer by layer through concept nodes and provisional nodes in current layer; the concept nodes are found parent-child relationships upward layer by layer, then the Hasse diagram of inter-layer connection is generated; in the generated process of the lattice nodes in each layer, we do the pruning operations dynamically according to relevant properties, and delete some unnecessary nodes, such that the generating speed is improved greatly; the experimental results demonstrate that the proposed algorithm has good performance.
Anomalous electrical resistivity of the Kondo system Ce(Rh1-xCox)3B2
Ku, H. C.; Yu, H.
1986-08-01
Electrical resistivity measurements have been carried out on the high-Curie-temperature ferromagnetic compound CeRh3B2 (TC=110-115 K). The temperature dependence of the electrical resistivity ρ(T) during the initial cooldown above TC gives the first solid indication of the Kondo-like behavior in this system. However, the resisitivity is irreversible above TC when warming up from low temperature and ρ(T) approaches the previous reported form. This irreversibility is closely related to microscopic cracks created by the strong internal magnetic field of the ferromagnetic state and was not observed in the nonmagnetic compound CeCo3B2 with the same hexagonal structure. Further proof of this Kondo state can be obtained in the study of the pseudoternary system Ce(Rh1-xCox)3B2 where the resistivity increases with decreasing temperature during the initial cooldown and a local minimum Kondo anomaly was observed. The magnetic state is rapidly broken up with the replacement of Rh by Co and the resistivity anomaly disappears after the disappearance of ferromagnetic order.
Institute of Scientific and Technical Information of China (English)
CHEN Xiong-Wen; SHI Zhen-Gang; CHEN Bao-Ju; SONG Ke-Hui
2007-01-01
We analyse the transport properties of a coupled double quantum dot (DQD) device with one of the dots (QD1) coupled to metallic leads and the other (QD2) embedded in an Aharonov-Bhom (A-B) ring by means of the slave-boson mean-Geld theory. It is found that in this system, the Kondo resonance and the Fano interference exist simultaneously, the enhancing Kondo effect and the increasing hopping of the QD2-Ring destroy the localized electron state in the QD2 for the QD1-leads, and accordingly, the Fano interference between the DQD-leads and the QD1-leads are suppressed. Under some conditions, the Fano interference can be quenched fully and the single Kondo resonance of the QD1-leads comes into being. Moreover, when the magnetic flux of the A-B ring is zero, the influence of the parity of the A-B ring on the transport properties is very weak, but this inSuence becomes more obvious with non-zero magnetic flux. Thus this model may be a candidate for future device applications.
Shigaki, Kenta; Noda, Fumiaki; Yamamoto, Kazami; Machida, Shinji; Molodojentsev, Alexander; Ishi, Yoshihiro
2002-12-01
The JKJ high-intensity proton accelerator facility consists of a 400-MeV linac, a 3-GeV 1-MW rapid-cycling synchrotron and a 50-GeV 0.75-MW synchrotron. The lattice and beam dynamics design of the two synchrotrons are reported.
de Raedt, Hans; von der Linden, W.; Binder, K
1995-01-01
In this chapter we review methods currently used to perform Monte Carlo calculations for quantum lattice models. A detailed exposition is given of the formalism underlying the construction of the simulation algorithms. We discuss the fundamental and technical difficulties that are encountered and gi
Knuth, Kevin H
2009-01-01
Previous derivations of the sum and product rules of probability theory relied on the algebraic properties of Boolean logic. Here they are derived within a more general framework based on lattice theory. The result is a new foundation of probability theory that encompasses and generalizes both the Cox and Kolmogorov formulations. In this picture probability is a bi-valuation defined on a lattice of statements that quantifies the degree to which one statement implies another. The sum rule is a constraint equation that ensures that valuations are assigned so as to not violate associativity of the lattice join and meet. The product rule is much more interesting in that there are actually two product rules: one is a constraint equation arises from associativity of the direct products of lattices, and the other a constraint equation derived from associativity of changes of context. The generality of this formalism enables one to derive the traditionally assumed condition of additivity in measure theory, as well in...
Williamson, S. Gill
2010-01-01
Will the cosmological multiverse, when described mathematically, have easily stated properties that are impossible to prove or disprove using mathematical physics? We explore this question by constructing lattice multiverses which exhibit such behavior even though they are much simpler mathematically than any likely cosmological multiverse.
Phenomenology from lattice QCD
Lellouch, L P
2003-01-01
After a short presentation of lattice QCD and some of its current practical limitations, I review recent progress in applications to phenomenology. Emphasis is placed on heavy-quark masses and on hadronic weak matrix elements relevant for constraining the CKM unitarity triangle. The main numerical results are highlighted in boxes.
Noetherian and Artinian Lattices
Directory of Open Access Journals (Sweden)
Derya Keskin Tütüncü
2012-01-01
Full Text Available It is proved that if L is a complete modular lattice which is compactly generated, then Rad(L/0 is Artinian if, and only if for every small element a of L, the sublattice a/0 is Artinian if, and only if L satisfies DCC on small elements.
Büsser, C. A.; Martins, G. B.; Feiguin, A. E.
2013-12-01
We present a completely unbiased and controlled numerical method to solve quantum impurity problems in d-dimensional lattices. This approach is based on a canonical transformation, of the Lanczos form, where the complete lattice Hamiltonian is exactly mapped onto an equivalent one-dimensional system, in the same spirit as Wilson's numerical renormalization, and Haydock's recursion method. We introduce many-body interactions in the form of a Kondo or Anderson impurity and we solve the low-dimensional problem using the density matrix renormalization group. The technique is particularly suited to study systems that are inhomogeneous, and/or have a boundary. The resulting dimensional reduction translates into a reduction of the scaling of the entanglement entropy by a factor Ld-1, where L is the linear dimension of the original d-dimensional lattice. This allows one to calculate the ground state of a magnetic impurity attached to an L×L square lattice and an L×L×L cubic lattice with L up to 140 sites. We also study the localized edge states in graphene nanoribbons by attaching a magnetic impurity to the edge or the center of the system. For armchair metallic nanoribbons we find a slow decay of the spin correlations as a consequence of the delocalized metallic states. In the case of zigzag ribbons, the decay of the spin correlations depends on the position of the impurity. If the impurity is situated in the bulk of the ribbon, the decay is slow as in the metallic case. On the other hand, if the adatom is attached to the edge, the decay is fast, within few sites of the impurity, as a consequence of the localized edge states, and the short correlation length. The mapping can be combined with ab initio band structure calculations to model the system, and to understand correlation effects in quantum impurity problems starting from first principles.
Basis reduction for layered lattices
Torreão Dassen, Erwin
2011-01-01
We develop the theory of layered Euclidean spaces and layered lattices. We present algorithms to compute both Gram-Schmidt and reduced bases in this generalized setting. A layered lattice can be seen as lattices where certain directions have infinite weight. It can also be interpre
Spin qubits in antidot lattices
DEFF Research Database (Denmark)
Pedersen, Jesper Goor; Flindt, Christian; Mortensen, Niels Asger;
2008-01-01
and density of states for a periodic potential modulation, referred to as an antidot lattice, and find that localized states appear, when designed defects are introduced in the lattice. Such defect states may form the building blocks for quantum computing in a large antidot lattice, allowing for coherent...
Kondo Physics at Interfaces in Metallic Non-Local Spin Transport Devices
Leighton, Chris
2015-03-01
Despite the maturity of metallic spintronics there remain large gaps in our understanding of spin transport in metals, particularly with injection of spins across ferromagnetic/non-magnetic (FM/NM) interfaces, and their subsequent diffusion and relaxation. Unresolved issues include the limits of applicability of Elliott-Yafet spin relaxation, quantification of the influence of defects, surfaces, and interfaces on spin relaxation at nanoscopic dimensions, and the importance of magnetic and spin-orbit scattering. The non-local spin-valve is an enabling device in this context as, in addition to offering potentially disruptive applications, it allows for the separation of charge and spin currents. One particularly perplexing issue in metallic non-local spin valves is the widely observed non-monotonicity in the T-dependent spin accumulation, where the spin signal actually decreases at low T, in contrast to simple expectations. In this work, by studying an expanded range of FM/NM combinations (encompassing Ni80Fe20, Ni, Fe, Co, Cu, and Al), we demonstrate that this effect is not a property of a given FM or NM, but rather of the FM/NM pair. The non-monotonicity is in fact strongly correlated with the ability of the FM to form a dilute local magnetic moment in the NM. We show that local moments, resulting in this case from the ppm-level tail of the FM/NM interdiffusion profile, suppress the injected spin polarization and diffusion length via a novel manifestation of the Kondo effect, explaining all observations associated with the low T downturn in spin accumulation. We further show: (a) that this effect can be promoted by thermal annealing, at which point the conventional charge transport Kondo effect is simultaneously detected in the NM, and (b) that this suppression in spin accumulation can be quenched, even at interfaces that are highly susceptible to the effect, by insertion of a thin non-moment-supporting interlayer. Important implications for room temperature
Energy Technology Data Exchange (ETDEWEB)
Gupta, R.
1998-12-31
The goal of the lectures on lattice QCD (LQCD) is to provide an overview of both the technical issues and the progress made so far in obtaining phenomenologically useful numbers. The lectures consist of three parts. The author`s charter is to provide an introduction to LQCD and outline the scope of LQCD calculations. In the second set of lectures, Guido Martinelli will discuss the progress they have made so far in obtaining results, and their impact on Standard Model phenomenology. Finally, Martin Luescher will discuss the topical subjects of chiral symmetry, improved formulation of lattice QCD, and the impact these improvements will have on the quality of results expected from the next generation of simulations.
Lattice Quantum Chromodynamics
Sachrajda, C. T.
2016-10-01
I review the the application of the lattice formulation of QCD and large-scale numerical simulations to the evaluation of non-perturbative hadronic effects in Standard Model Phenomenology. I present an introduction to the elements of the calculations and discuss the limitations both in the range of quantities which can be studied and in the precision of the results. I focus particularly on the extraction of the QCD parameters, i.e. the quark masses and the strong coupling constant, and on important quantities in flavour physics. Lattice QCD is playing a central role in quantifying the hadronic effects necessary for the development of precision flavour physics and its use in exploring the limits of the Standard Model and in searches for inconsistencies which would signal the presence of new physics.
Lattices of dielectric resonators
Trubin, Alexander
2016-01-01
This book provides the analytical theory of complex systems composed of a large number of high-Q dielectric resonators. Spherical and cylindrical dielectric resonators with inferior and also whispering gallery oscillations allocated in various lattices are considered. A new approach to S-matrix parameter calculations based on perturbation theory of Maxwell equations, developed for a number of high-Q dielectric bodies, is introduced. All physical relationships are obtained in analytical form and are suitable for further computations. Essential attention is given to a new unified formalism of the description of scattering processes. The general scattering task for coupled eigen oscillations of the whole system of dielectric resonators is described. The equations for the expansion coefficients are explained in an applicable way. The temporal Green functions for the dielectric resonator are presented. The scattering process of short pulses in dielectric filter structures, dielectric antennas and lattices of d...
Fractional lattice charge transport
Flach, Sergej; Khomeriki, Ramaz
2017-01-01
We consider the dynamics of noninteracting quantum particles on a square lattice in the presence of a magnetic flux α and a dc electric field E oriented along the lattice diagonal. In general, the adiabatic dynamics will be characterized by Bloch oscillations in the electrical field direction and dispersive ballistic transport in the perpendicular direction. For rational values of α and a corresponding discrete set of values of E(α) vanishing gaps in the spectrum induce a fractionalization of the charge in the perpendicular direction - while left movers are still performing dispersive ballistic transport, the complementary fraction of right movers is propagating in a dispersionless relativistic manner in the opposite direction. Generalizations and the possible probing of the effect with atomic Bose-Einstein condensates and photonic networks are discussed. Zak phase of respective band associated with gap closing regime has been computed and it is found converging to π/2 value. PMID:28102302
Borsanyi, Sz; Kampert, K H; Katz, S D; Kawanai, T; Kovacs, T G; Mages, S W; Pasztor, A; Pittler, F; Redondo, J; Ringwald, A; Szabo, K K
2016-01-01
We present a full result for the equation of state (EoS) in 2+1+1 (up/down, strange and charm quarks are present) flavour lattice QCD. We extend this analysis and give the equation of state in 2+1+1+1 flavour QCD. In order to describe the evolution of the universe from temperatures several hundreds of GeV to several tens of MeV we also include the known effects of the electroweak theory and give the effective degree of freedoms. As another application of lattice QCD we calculate the topological susceptibility (chi) up to the few GeV temperature region. These two results, EoS and chi, can be used to predict the dark matter axion's mass in the post-inflation scenario and/or give the relationship between the axion's mass and the universal axionic angle, which acts as a initial condition of our universe.
Solitons in nonlinear lattices
Kartashov, Yaroslav V; Torner, Lluis
2010-01-01
This article offers a comprehensive survey of results obtained for solitons and complex nonlinear wave patterns supported by purely nonlinear lattices (NLs), which represent a spatially periodic modulation of the local strength and sign of the nonlinearity, and their combinations with linear lattices. A majority of the results obtained, thus far, in this field and reviewed in this article are theoretical. Nevertheless, relevant experimental settings are surveyed too, with emphasis on perspectives for implementation of the theoretical predictions in the experiment. Physical systems discussed in the review belong to the realms of nonlinear optics (including artificial optical media, such as photonic crystals, and plasmonics) and Bose-Einstein condensation (BEC). The solitons are considered in one, two, and three dimensions (1D, 2D, and 3D). Basic properties of the solitons presented in the review are their existence, stability, and mobility. Although the field is still far from completion, general conclusions c...
Parametric lattice Boltzmann method
Shim, Jae Wan
2017-06-01
The discretized equilibrium distributions of the lattice Boltzmann method are presented by using the coefficients of the Lagrange interpolating polynomials that pass through the points related to discrete velocities and using moments of the Maxwell-Boltzmann distribution. The ranges of flow velocity and temperature providing positive valued distributions vary with regulating discrete velocities as parameters. New isothermal and thermal compressible models are proposed for flows of the level of the isothermal and thermal compressible Navier-Stokes equations. Thermal compressible shock tube flows are simulated by only five on-lattice discrete velocities. Two-dimensional isothermal and thermal vortices provoked by the Kelvin-Helmholtz instability are simulated by the parametric models.
Jipsen, Peter
1992-01-01
The study of lattice varieties is a field that has experienced rapid growth in the last 30 years, but many of the interesting and deep results discovered in that period have so far only appeared in research papers. The aim of this monograph is to present the main results about modular and nonmodular varieties, equational bases and the amalgamation property in a uniform way. The first chapter covers preliminaries that make the material accessible to anyone who has had an introductory course in universal algebra. Each subsequent chapter begins with a short historical introduction which sites the original references and then presents the results with complete proofs (in nearly all cases). Numerous diagrams illustrate the beauty of lattice theory and aid in the visualization of many proofs. An extensive index and bibliography also make the monograph a useful reference work.
Lattice Quantum Chromodynamics
Sachrajda, C T
2016-01-01
I review the the application of the lattice formulation of QCD and large-scale numerical simulations to the evaluation of non-perturbative hadronic effects in Standard Model Phenomenology. I present an introduction to the elements of the calculations and discuss the limitations both in the range of quantities which can be studied and in the precision of the results. I focus particularly on the extraction of the QCD parameters, i.e. the quark masses and the strong coupling constant, and on important quantities in flavour physics. Lattice QCD is playing a central role in quantifying the hadronic effects necessary for the development of precision flavour physics and its use in exploring the limits of the Standard Model and in searches for inconsistencies which would signal the presence of new physics.
International Lattice Data Grid
Davies, C T H; Kenway, R D; Maynard, C M
2002-01-01
We propose the co-ordination of lattice QCD grid developments in different countries to allow transparent exchange of gauge configurations in future, should participants wish to do so. We describe briefly UKQCD's XML schema for labelling and cataloguing the data. A meeting to further develop these ideas will be held in Edinburgh on 19/20 December 2002, and will be available over AccessGrid.
Weakly deformed soliton lattices
Energy Technology Data Exchange (ETDEWEB)
Dubrovin, B. (Moskovskij Gosudarstvennyj Univ., Moscow (USSR). Dept. of Mechanics and Mathematics)
1990-12-01
In this lecture the author discusses periodic and quasiperiodic solutions of nonlinear evolution equations of phi{sub t}=K (phi, phi{sub x},..., phi{sup (n)}), the so-called soliton lattices. After introducing the theory of integrable systems of hydrodynamic type he discusses their Hamiltonian formalism, i.e. the theory of Poisson brackets of hydrodynamic type. Then he describes the application of algebraic geometry to the effective integration of such equations. (HSI).
Crystallographic Lattice Boltzmann Method
Namburi, Manjusha; Krithivasan, Siddharth; Ansumali, Santosh
2016-01-01
Current approaches to Direct Numerical Simulation (DNS) are computationally quite expensive for most realistic scientific and engineering applications of Fluid Dynamics such as automobiles or atmospheric flows. The Lattice Boltzmann Method (LBM), with its simplified kinetic descriptions, has emerged as an important tool for simulating hydrodynamics. In a heterogeneous computing environment, it is often preferred due to its flexibility and better parallel scaling. However, direct simulation of realistic applications, without the use of turbulence models, remains a distant dream even with highly efficient methods such as LBM. In LBM, a fictitious lattice with suitable isotropy in the velocity space is considered to recover Navier-Stokes hydrodynamics in macroscopic limit. The same lattice is mapped onto a cartesian grid for spatial discretization of the kinetic equation. In this paper, we present an inverted argument of the LBM, by making spatial discretization as the central theme. We argue that the optimal spatial discretization for LBM is a Body Centered Cubic (BCC) arrangement of grid points. We illustrate an order-of-magnitude gain in efficiency for LBM and thus a significant progress towards feasibility of DNS for realistic flows. PMID:27251098
Bietenholz, W; Pepe, M; Wiese, U -J
2010-01-01
We consider lattice field theories with topological actions, which are invariant against small deformations of the fields. Some of these actions have infinite barriers separating different topological sectors. Topological actions do not have the correct classical continuum limit and they cannot be treated using perturbation theory, but they still yield the correct quantum continuum limit. To show this, we present analytic studies of the 1-d O(2) and O(3) model, as well as Monte Carlo simulations of the 2-d O(3) model using topological lattice actions. Some topological actions obey and others violate a lattice Schwarz inequality between the action and the topological charge $Q$. Irrespective of this, in the 2-d O(3) model the topological susceptibility $\\chi_t = \\l/V$ is logarithmically divergent in the continuum limit. Still, at non-zero distance the correlator of the topological charge density has a finite continuum limit which is consistent with analytic predictions. Our study shows explicitly that some cla...
Adamatzky, Andrew
2015-01-01
The book gives a comprehensive overview of the state-of-the-art research and engineering in theory and application of Lattice Automata in design and control of autonomous Robots. Automata and robots share the same notional meaning. Automata (originated from the latinization of the Greek word “αυτόματον”) as self-operating autonomous machines invented from ancient years can be easily considered the first steps of robotic-like efforts. Automata are mathematical models of Robots and also they are integral parts of robotic control systems. A Lattice Automaton is a regular array or a collective of finite state machines, or automata. The Automata update their states by the same rules depending on states of their immediate neighbours. In the context of this book, Lattice Automata are used in developing modular reconfigurable robotic systems, path planning and map exploration for robots, as robot controllers, synchronisation of robot collectives, robot vision, parallel robotic actuators. All chapters are...
Hadroquarkonium from lattice QCD
Alberti, Maurizio; Bali, Gunnar S.; Collins, Sara; Knechtli, Francesco; Moir, Graham; Söldner, Wolfgang
2017-04-01
The hadroquarkonium picture [S. Dubynskiy and M. B. Voloshin, Phys. Lett. B 666, 344 (2008), 10.1016/j.physletb.2008.07.086] provides one possible interpretation for the pentaquark candidates with hidden charm, recently reported by the LHCb Collaboration, as well as for some of the charmoniumlike "X , Y , Z " states. In this picture, a heavy quarkonium core resides within a light hadron giving rise to four- or five-quark/antiquark bound states. We test this scenario in the heavy quark limit by investigating the modification of the potential between a static quark-antiquark pair induced by the presence of a hadron. Our lattice QCD simulations are performed on a Coordinated Lattice Simulations (CLS) ensemble with Nf=2 +1 flavors of nonperturbatively improved Wilson quarks at a pion mass of about 223 MeV and a lattice spacing of about a =0.0854 fm . We study the static potential in the presence of a variety of light mesons as well as of octet and decuplet baryons. In all these cases, the resulting configurations are favored energetically. The associated binding energies between the quarkonium in the heavy quark limit and the light hadron are found to be smaller than a few MeV, similar in strength to deuterium binding. It needs to be seen if the small attraction survives in the infinite volume limit and supports bound states or resonances.
Digital lattice gauge theories
Zohar, Erez; Farace, Alessandro; Reznik, Benni; Cirac, J. Ignacio
2017-02-01
We propose a general scheme for a digital construction of lattice gauge theories with dynamical fermions. In this method, the four-body interactions arising in models with 2 +1 dimensions and higher are obtained stroboscopically, through a sequence of two-body interactions with ancillary degrees of freedom. This yields stronger interactions than the ones obtained through perturbative methods, as typically done in previous proposals, and removes an important bottleneck in the road towards experimental realizations. The scheme applies to generic gauge theories with Lie or finite symmetry groups, both Abelian and non-Abelian. As a concrete example, we present the construction of a digital quantum simulator for a Z3 lattice gauge theory with dynamical fermionic matter in 2 +1 dimensions, using ultracold atoms in optical lattices, involving three atomic species, representing the matter, gauge, and auxiliary degrees of freedom, that are separated in three different layers. By moving the ancilla atoms with a proper sequence of steps, we show how we can obtain the desired evolution in a clean, controlled way.
Yeganeh, Mohammad; Dashti, Mohsen; Slussarenko, Sergei; Santamato, Enrico; Karimi, Ebrahim
2013-01-01
A novel approach based on the two-channel moir\\'e deflectometry has been used to measure both wave-front and transverse component of the Poynting vector of an optical vortex beam. Generated vortex beam by the q-plate, an inhomogeneous liquid crystal cell, has been analyzed with such technique. The measured topological charge of generated beams are in an excellent agreement with theoretical prediction.
A Mechanical Lattice Aid for Crystallography Teaching.
Amezcua-Lopez, J.; Cordero-Borboa, A. E.
1988-01-01
Introduces a 3-dimensional mechanical lattice with adjustable telescoping mechanisms. Discusses the crystalline state, the 14 Bravais lattices, operational principles of the mechanical lattice, construction methods, and demonstrations in classroom. Provides lattice diagrams, schemes of the lattice, and various pictures of the lattice. (YP)
Kenneth Wilson and lattice QCD
Ukawa, Akira
2015-01-01
We discuss the physics and computation of lattice QCD, a space-time lattice formulation of quantum chromodynamics, and Kenneth Wilson's seminal role in its development. We start with the fundamental issue of confinement of quarks in the theory of the strong interactions, and discuss how lattice QCD provides a framework for understanding this phenomenon. A conceptual issue with lattice QCD is a conflict of space-time lattice with chiral symmetry of quarks. We discuss how this problem is resolved. Since lattice QCD is a non-linear quantum dynamical system with infinite degrees of freedom, quantities which are analytically calculable are limited. On the other hand, it provides an ideal case of massively parallel numerical computations. We review the long and distinguished history of parallel-architecture supercomputers designed and built for lattice QCD. We discuss algorithmic developments, in particular the difficulties posed by the fermionic nature of quarks, and their resolution. The triad of efforts toward b...
Tuning bulk and surface conduction in the proposed topological Kondo insulator SmB(6).
Syers, Paul; Kim, Dohun; Fuhrer, Michael S; Paglione, Johnpierre
2015-03-06
Bulk and surface state contributions to the electrical resistance of single-crystal samples of the topological Kondo-insulator compound SmB_{6} are investigated as a function of crystal thickness and surface charge density, the latter tuned by ionic liquid gating with electrodes patterned in a Corbino disk geometry on a single (100) surface. By separately tuning bulk and surface conduction channels, we show conclusive evidence for a model with an insulating bulk and metallic surface states, with a crossover temperature that depends solely on the relative contributions of each conduction channel. The surface conductance, on the order of 100 e^{2}/h, exhibits a field-effect mobility of 133 cm^{2}/Vs and a large carrier density of ∼2×10^{14} cm^{-2}, in good agreement with recent photoemission results. With the ability to gate modulate surface conduction by more than 25%, this approach provides promise for both fundamental and applied studies of gate-tuned devices structured on bulk crystal samples.
Energy Technology Data Exchange (ETDEWEB)
Zvyagin, A.A. [B. I. Verkin Institute for Low Temperature Physics and Engineering of the National Ukrainian Academy of Sciences, 47, Lenin Avenue, 310164, Kharkov (Ukraine); Schlottmann, P. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States)
1996-12-01
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 {Gamma}{sub 8} into two doublets in the quadrupolar Kondo effect, or to the electron-assisted tunneling of an atom in a double-well potential in an external magnetic field. Another possible realization could be a quantum dot coupled to two equal rings of the same length subject to an electrostatic potential difference. We consider the Bethe ansatz equations for this model and derive the tower structure of the finite-size corrections to the ground-state energy. These results are used to discuss the Aharonov-Bohm-Casher interference pattern in the persistent charge and spin currents, and the magnetoresistivity due to the scattering of electrons off the impurity. {copyright} {ital 1996 The American Physical Society.}
Kondo effect and quantum critical point in Mn(1-x)CoxSi
Teyssier, J.; Viennois, R.; Guritanu, V.; Giannini, E.; van der Marel, D.
2010-01-01
We report magnetic, transport and neutron diffraction studies of the solid solution Mn1-xCoxSi. For the Mn rich compounds, a sharp decrease of the Curie temperature is observed upon cobalt doping and neutron elastic scattering shows that the helimagnetic order of MnSi persists up to x = 0.06 with a shortening of the helix period. For higher Co concentrations (0.06 Weiss temperature changes sign and the system enters an antiferromagnetic state upon cooling (TN=9K for x = 0.50). In this doping range, the antiferromagnetic coupling leads to a Kondo effect marked by a minimum in the resistivity. This scenario is supported by the scaling of the magnetoresistance with a TK approx 6.5 K, close to the change in curvature of the resistivity and in agreement with the Weiss temperature from magnetic susceptibility. The sign change of the Weiss temperature and the transition from a helimagnetic to an antiferromagnetic ground state, with increasing the Co doping, point toward the existence of a quantum critical point at the composition Mn0.94Co0.06Si.
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.
Transport properties of the topological Kondo insulator SmB6 under the irradiation of light
Zhu, Guo-Bao; Yang, Hui-Min
2016-10-01
In this paper, we study transport properties of the X point in the Brillouin zone of the topological Kondo insulator SmB6 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. Project supported by the National Natural Science Foundation of China (Grant Nos. 11504095 and 11447145), the Foundation of Heze University (Grant Nos. XY14B002 and XYPY01), and the Project funded by the Higher Educational Science and Technology Program of Shandong Province, China (Grant No. J15LJ55).
Phase boundaries of power-law Anderson and Kondo models: A poor man's scaling study
Cheng, Mengxing; Chowdhury, Tathagata; Mohammed, Aaron; Ingersent, Kevin
2017-07-01
We use the poor man's scaling approach to study the phase boundaries of a pair of quantum impurity models featuring a power-law density of states ρ (ɛ ) ∝|ɛ| r , either vanishing (for r >0 ) or diverging (for r 0 ), we find the phase boundary for (a) 0 1 , where the phases are separated by first-order quantum phase transitions that are accessible only for broken p-h symmetry. For the p-h-symmetric Kondo model with easy-axis or easy-plane anisotropy of the impurity-band spin exchange, the phase boundary and scaling trajectories are obtained for both r >0 and r <0 . Throughout the regime of weak-to-moderate impurity-band coupling in which poor man's scaling is expected to be valid, the approach predicts phase boundaries in excellent qualitative and good quantitative agreement with the nonperturbative numerical renormalization group, while also establishing the functional relations between model parameters along these boundaries.
Lattice topology dictates photon statistics.
Kondakci, H Esat; Abouraddy, Ayman F; Saleh, Bahaa E A
2017-08-21
Propagation of coherent light through a disordered network is accompanied by randomization and possible conversion into thermal light. Here, we show that network topology plays a decisive role in determining the statistics of the emerging field if the underlying lattice is endowed with chiral symmetry. In such lattices, eigenmode pairs come in skew-symmetric pairs with oppositely signed eigenvalues. By examining one-dimensional arrays of randomly coupled waveguides arranged on linear and ring topologies, we are led to a remarkable prediction: the field circularity and the photon statistics in ring lattices are dictated by its parity while the same quantities are insensitive to the parity of a linear lattice. For a ring lattice, adding or subtracting a single lattice site can switch the photon statistics from super-thermal to sub-thermal, or vice versa. This behavior is understood by examining the real and imaginary fields on a lattice exhibiting chiral symmetry, which form two strands that interleave along the lattice sites. These strands can be fully braided around an even-sited ring lattice thereby producing super-thermal photon statistics, while an odd-sited lattice is incommensurate with such an arrangement and the statistics become sub-thermal.
Drashkovicheva, Kh; Igoshin, V I; Katrinyak, T; Kolibiar, M
1989-01-01
This book is another publication in the recent surveys of ordered sets and lattices. The papers, which might be characterized as "reviews of reviews," are based on articles reviewed in the Referativnyibreve Zhurnal: Matematika from 1978 to 1982. For the sake of completeness, the authors also attempted to integrate information from other relevant articles from that period. The bibliography of each paper provides references to the reviews in RZhMat and Mathematical Reviews where one can seek more detailed information. Specifically excluded from consideration in this volume were such topics as al
Lattice Vibrations in Chlorobenzenes:
DEFF Research Database (Denmark)
Reynolds, P. A.; Kjems, Jørgen; White, J. W.
1974-01-01
Lattice vibrational dispersion curves for the ``intermolecular'' modes in the triclinic, one molecule per unit cell β phase of p‐C6D4Cl2 and p‐C6H4Cl2 have been obtained by inelastic neutron scattering. The deuterated sample was investigated at 295 and at 90°K and a linear extrapolation to 0°K...... by consideration of electrostatic forces or by further anisotropy in the dispersion forces not described in the atom‐atom model. Anharmonic effects are shown to be large, but the dominant features in the temperature variation of frequencies are describable by a quasiharmonic model....
Muñoz, Enrique; Bolech, C J; Kirchner, Stefan
2013-01-04
The nonlinear conductance of semiconductor heterostructures and single molecule devices exhibiting Kondo physics has recently attracted attention. We address the observed sample dependence of the measured steady state transport coefficients by considering additional electronic contributions in the effective low-energy model underlying these experiments that are absent in particle-hole symmetric setups. A novel version of the superperturbation theory of Hafermann et al. in terms of dual fermions is developed, which correctly captures the low-temperature behavior. We compare our results with the measured transport coefficients.
Lattice harmonics expansion revisited
Kontrym-Sznajd, G.; Holas, A.
2017-04-01
The main subject of the work is to provide the most effective way of determining the expansion of some quantities into orthogonal polynomials, when these quantities are known only along some limited number of sampling directions. By comparing the commonly used Houston method with the method based on the orthogonality relation, some relationships, which define the applicability and correctness of these methods, are demonstrated. They are verified for various sets of sampling directions applicable for expanding quantities having the full symmetry of the Brillouin zone of cubic and non-cubic lattices. All results clearly show that the Houston method is always better than the orthogonality-relation one. For the cubic symmetry we present a few sets of special directions (SDs) showing how their construction and, next, a proper application depend on the choice of various sets of lattice harmonics. SDs are important mainly for experimentalists who want to reconstruct anisotropic quantities from their measurements, performed at a limited number of sampling directions.
Extreme lattices: symmetries and decorrelation
Andreanov, A.; Scardicchio, A.; Torquato, S.
2016-11-01
We study statistical and structural properties of extreme lattices, which are the local minima in the density landscape of lattice sphere packings in d-dimensional Euclidean space {{{R}}d} . Specifically, we ascertain statistics of the densities and kissing numbers as well as the numbers of distinct symmetries of the packings for dimensions 8 through 13 using the stochastic Voronoi algorithm. The extreme lattices in a fixed dimension of space d (d≥slant 8 ) are dominated by typical lattices that have similar packing properties, such as packing densities and kissing numbers, while the best and the worst packers are in the long tails of the distribution of the extreme lattices. We also study the validity of the recently proposed decorrelation principle, which has important implications for sphere packings in general. The degree to which extreme-lattice packings decorrelate as well as how decorrelation is related to the packing density and symmetry of the lattices as the space dimension increases is also investigated. We find that the extreme lattices decorrelate with increasing dimension, while the least symmetric lattices decorrelate faster.
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
Elimination of spurious lattice fermion solutions and noncompact lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Lee, T.D.
1997-09-22
It is well known that the Dirac equation on a discrete hyper-cubic lattice in D dimension has 2{sup D} degenerate solutions. The usual method of removing these spurious solutions encounters difficulties with chiral symmetry when the lattice spacing l {ne} 0, as exemplified by the persistent problem of the pion mass. On the other hand, we recall that in any crystal in nature, all the electrons do move in a lattice and satisfy the Dirac equation; yet there is not a single physical result that has ever been entangled with a spurious fermion solution. Therefore it should not be difficult to eliminate these unphysical elements. On a discrete lattice, particle hop from point to point, whereas in a real crystal the lattice structure in embedded in a continuum and electrons move continuously from lattice cell to lattice cell. In a discrete system, the lattice functions are defined only on individual points (or links as in the case of gauge fields). However, in a crystal the electron state vector is represented by the Bloch wave functions which are continuous functions in {rvec {gamma}}, and herein lies one of the essential differences.
Lattice Boltzmann Model for Compressible Fluid on a Square Lattice
Institute of Scientific and Technical Information of China (English)
SUN Cheng-Hai
2000-01-01
A two-level four-direction lattice Boltzmann model is formulated on a square lattice to simulate compressible flows with a high Mach number. The particle velocities are adaptive to the mean velocity and internal energy. Therefore, the mean flow can have a high Mach number. Due to the simple form of the equilibrium distribution, the 4th order velocity tensors are not involved in the calculations. Unlike the standard lattice Boltzmann model, o special treatment is need for the homogeneity of 4th order velocity tensors on square lattices. The Navier-Stokes equations were derived by the Chapman-Enskog method from the BGK Boltzmann equation. The model can be easily extended to three-dimensional cubic lattices. Two-dimensional shock-wave propagation was simulated
Entangling gates in even Euclidean lattices such as Leech lattice
Planat, Michel
2010-01-01
We point out a organic relationship between real entangling n-qubit gates of quantum computation and the group of automorphisms of even Euclidean lattices of the corresponding dimension 2n. The type of entanglement that is found in the gates/generators of Aut() depends on the lattice. In particular, we investigate Zn lattices, Barnes-Wall lattices D4, E8, 16 (associated to n = 2, 3 and 4 qubits), and the Leech lattices h24 and 24 (associated to a 3-qubit/qutrit system). Balanced tripartite entanglement is found to be a basic feature of Aut(), a nding that bears out our recent work related to the Weyl group of E8 [1, 2].
Introduction to lattice gauge theory
Gupta, R.
The lattice formulation of Quantum Field Theory (QFT) can be exploited in many ways. We can derive the lattice Feynman rules and carry out weak coupling perturbation expansions. The lattice then serves as a manifestly gauge invariant regularization scheme, albeit one that is more complicated than standard continuum schemes. Strong coupling expansions: these give us useful qualitative information, but unfortunately no hard numbers. The lattice theory is amenable to numerical simulations by which one calculates the long distance properties of a strongly interacting theory from first principles. The observables are measured as a function of the bare coupling g and a gauge invariant cut-off approx. = 1/alpha, where alpha is the lattice spacing. The continuum (physical) behavior is recovered in the limit alpha yields 0, at which point the lattice artifacts go to zero. This is the more powerful use of lattice formulation, so in these lectures the author focuses on setting up the theory for the purpose of numerical simulations to get hard numbers. The numerical techniques used in Lattice Gauge Theories have their roots in statistical mechanics, so it is important to develop an intuition for the interconnection between quantum mechanics and statistical mechanics.
Lewis, Randy
2014-01-01
Several collaborations have recently performed lattice calculations aimed specifically at dark matter, including work with SU(2), SU(3), SU(4) and SO(4) gauge theories to represent the dark sector. Highlights of these studies are presented here, after a reminder of how lattice calculations in QCD itself are helping with the hunt for dark matter.
Fast simulation of lattice systems
DEFF Research Database (Denmark)
Bohr, H.; Kaznelson, E.; Hansen, Frank;
1983-01-01
A new computer system with an entirely new processor design is described and demonstrated on a very small trial lattice. The new computer simulates systems of differential equations of the order of 104 times faster than present day computers and we describe how the machine can be applied to lattice...
Branes and integrable lattice models
Yagi, Junya
2016-01-01
This is a brief review of my work on the correspondence between four-dimensional $\\mathcal{N} = 1$ supersymmetric field theories realized by brane tilings and two-dimensional integrable lattice models. I explain how to construct integrable lattice models from extended operators in partially topological quantum field theories, and elucidate the correspondence as an application of this construction.
Charmed baryons on the lattice
Padmanath, M
2015-01-01
We discuss the significance of charm baryon spectroscopy in hadron physics and review the recent developments of the spectra of charmed baryons in lattice calculations. Special emphasis is given on the recent studies of highly excited charm baryon states. Recent precision lattice measurements of the low lying charm and bottom baryons are also reviewed.
Quantum phases in optical lattices
Dickerscheid, Dennis Brian Martin
2006-01-01
An important new development in the field of ultracold atomic gases is the study of the properties of these gases in a so-called optical lattice. An optical lattice is a periodic trapping potential for the atoms that is formed by the interference pattern of a few laser beams. A reason for the
Light induced suppression of Kondo effect at amorphous LaAlO3/SrTiO3 interface
Liu, G. Z.; Qiu, J.; Jiang, Y. C.; Zhao, R.; Yao, J. L.; Zhao, M.; Feng, Y.; Gao, J.
2016-07-01
We report photoelectric properties of two-dimensional electron gas (2DEG) at an amorphous LaAlO3/SrTiO3 interface. Under visible light illumination (650 nm), an enhancement of electric conductivity is observed over the temperature range from 2 to 300 K. Particularly, a resistance upturn appearing below 25 K, which is further proved to from the Kondo effect, is suppressed by the 650 nm visible light. From the results of light-assisted Hall measurements, light irradiation increases the carrier mobility rather than carrier density in the Kondo regime. It is suggested that light induces the decoherence effect of localized spin states, hence the electron scattering is weakened and the carrier mobility is improved accordingly. Moreover, the enhancement of electrical conductivity by visible light verifies that in-gap states located in the SrTiO3 side of the interface play an important role in the electrical transport of the amorphous SrTiO3-based oxide 2DEG system. Our results provide deeper insight into the photoinduced effects in the 2DEG system, paving the way for the design of optoelectronic devices based on oxides.
Lattice Induced Transparency in Metasurfaces
Manjappa, Manukumara; Singh, Ranjan
2016-01-01
Lattice modes are intrinsic to the periodic structures and their occurrence can be easily tuned and controlled by changing the lattice constant of the structural array. Previous studies have revealed excitation of sharp absorption resonances due to lattice mode coupling with the plasmonic resonances. Here, we report the first experimental observation of a lattice induced transparency (LIT) by coupling the first order lattice mode (FOLM) to the structural resonance of a metamaterial resonator at terahertz frequencies. The observed sharp transparency is a result of the destructive interference between the bright mode and the FOLM mediated dark mode. As the FOLM is swept across the metamaterial resonance, the transparency band undergoes large change in its bandwidth and resonance position. Besides controlling the transparency behaviour, LIT also shows a huge enhancement in the Q-factor and record high group delay of 28 ps, which could be pivotal in ultrasensitive sensing and slow light device applications.
Lattice models of ionic systems
Kobelev, Vladimir; Kolomeisky, Anatoly B.; Fisher, Michael E.
2002-05-01
A theoretical analysis of Coulomb systems on lattices in general dimensions is presented. The thermodynamics is developed using Debye-Hückel theory with ion-pairing and dipole-ion solvation, specific calculations being performed for three-dimensional lattices. As for continuum electrolytes, low-density results for simple cubic (sc), body-centered cubic (bcc), and face-centered cubic (fcc) lattices indicate the existence of gas-liquid phase separation. The predicted critical densities have values comparable to those of continuum ionic systems, while the critical temperatures are 60%-70% higher. However, when the possibility of sublattice ordering as well as Debye screening is taken into account systematically, order-disorder transitions and a tricritical point are found on sc and bcc lattices, and gas-liquid coexistence is suppressed. Our results agree with recent Monte Carlo simulations of lattice electrolytes.
Lattice quantum chromodynamics practical essentials
Knechtli, Francesco; Peardon, Michael
2017-01-01
This book provides an overview of the techniques central to lattice quantum chromodynamics, including modern developments. The book has four chapters. The first chapter explains the formulation of quarks and gluons on a Euclidean lattice. The second chapter introduces Monte Carlo methods and details the numerical algorithms to simulate lattice gauge fields. Chapter three explains the mathematical and numerical techniques needed to study quark fields and the computation of quark propagators. The fourth chapter is devoted to the physical observables constructed from lattice fields and explains how to measure them in simulations. The book is aimed at enabling graduate students who are new to the field to carry out explicitly the first steps and prepare them for research in lattice QCD.
Fermionic Optical Lattices: A Computational Study
2014-10-22
Kevin Schmidt, Shiwei Zhang. Auxiliary-field quantum Monte Carlo method for strongly paired fermions, Physical Review A, (12 2011): 0. doi...10.1103/PhysRevA.84.061602 A. Euverte, F. Hébert, S. Chiesa, R. Scalettar, G. Batrouni. Kondo Screening and Magnetism at Interfaces, Physical Review Letters...contact interaction: Magnetic properties in a dilute Hubbard model, Physical Review A, (12 2010): 0. doi: 10.1103/PhysRevA.82.061603 S. Zhou, D
Irreversible stochastic processes on lattices
Energy Technology Data Exchange (ETDEWEB)
Nord, R.S.
1986-01-01
Models for irreversible random or cooperative filling of lattices are required to describe many processes in chemistry and physics. Since the filling is assumed to be irreversible, even the stationary, saturation state is not in equilibrium. The kinetics and statistics of these processes are described by recasting the master equations in infinite hierarchical form. Solutions can be obtained by implementing various techniques: refinements in these solution techniques are presented. Programs considered include random dimer, trimer, and tetramer filling of 2D lattices, random dimer filling of a cubic lattice, competitive filling of two or more species, and the effect of a random distribution of inactive sites on the filling. Also considered is monomer filling of a linear lattice with nearest neighbor cooperative effects and solve for the exact cluster-size distribution for cluster sizes up to the asymptotic regime. Additionally, a technique is developed to directly determine the asymptotic properties of the cluster size distribution. Finally cluster growth is considered via irreversible aggregation involving random walkers. In particular, explicit results are provided for the large-lattice-size asymptotic behavior of trapping probabilities and average walk lengths for a single walker on a lattice with multiple traps. Procedures for exact calculation of these quantities on finite lattices are also developed.
Lattice topology dictates photon statistics
Kondakci, H Esat; Saleh, Bahaa E A
2016-01-01
Propagation of coherent light through a disordered network is accompanied by randomization and possible conversion into thermal light. Here, we show that network topology plays a decisive role in determining the statistics of the emerging field if the underlying lattice satisfies chiral symmetry. By examining one-dimensional arrays of randomly coupled waveguides arranged on linear and ring topologies, we are led to a remarkable prediction: the field circularity and the photon statistics in ring lattices are dictated by its parity -- whether the number of sites is even or odd, while the same quantities are insensitive to the parity of a linear lattice. Adding or subtracting a single lattice site can switch the photon statistics from super-thermal to sub-thermal, or vice versa. This behavior is understood by examining the real and imaginary fields on a chiral-symmetric lattice, which form two strands that interleave along the lattice sites. These strands can be fully braided around an even-sited ring lattice th...
Lattice Boltzmann model for nanofluids
Energy Technology Data Exchange (ETDEWEB)
Xuan Yimin; Yao Zhengping [Nanjing University of Science and Technology, School of Power Engineering, Nanjing (China)
2005-01-01
A nanofluid is a particle suspension that consists of base liquids and nanoparticles and has great potential for heat transfer enhancement. By accounting for the external and internal forces acting on the suspended nanoparticles and interactions among the nanoparticles and fluid particles, a lattice Boltzmann model is proposed for simulating flow and energy transport processes inside the nanofluids. First, we briefly introduce the conventional lattice Boltzmann model for multicomponent systems. Then, we discuss the irregular motion of the nanoparticles and inherent dynamic behavior of nanofluids and describe a lattice Boltzmann model for simulating nanofluids. Finally, we conduct some calculations for the distribution of the suspended nanoparticles. (orig.)
Localized structures in Kagome lattices
Energy Technology Data Exchange (ETDEWEB)
Saxena, Avadh B [Los Alamos National Laboratory; Bishop, Alan R [Los Alamos National Laboratory; Law, K J H [UNIV OF MASSACHUSETTS; Kevrekidis, P G [UNIV OF MASSACHUSETTS
2009-01-01
We investigate the existence and stability of gap vortices and multi-pole gap solitons in a Kagome lattice with a defocusing nonlinearity both in a discrete case and in a continuum one with periodic external modulation. In particular, predictions are made based on expansion around a simple and analytically tractable anti-continuum (zero coupling) limit. These predictions are then confirmed for a continuum model of an optically-induced Kagome lattice in a photorefractive crystal obtained by a continuous transformation of a honeycomb lattice.
Borwein, J M; McPhedran, R C
2013-01-01
The study of lattice sums began when early investigators wanted to go from mechanical properties of crystals to the properties of the atoms and ions from which they were built (the literature of Madelung's constant). A parallel literature was built around the optical properties of regular lattices of atoms (initiated by Lord Rayleigh, Lorentz and Lorenz). For over a century many famous scientists and mathematicians have delved into the properties of lattices, sometimes unwittingly duplicating the work of their predecessors. Here, at last, is a comprehensive overview of the substantial body of
Directory of Open Access Journals (Sweden)
Brian Jefferies
2014-01-01
Full Text Available A bounded linear operator T on a Hilbert space ℋ is trace class if its singular values are summable. The trace class operators on ℋ form an operator ideal and in the case that ℋ is finite-dimensional, the trace tr(T of T is given by ∑jajj for any matrix representation {aij} of T. In applications of trace class operators to scattering theory and representation theory, the subject is complicated by the fact that if k is an integral kernel of the operator T on the Hilbert space L2(μ with μ a σ-finite measure, then k(x,x may not be defined, because the diagonal {(x,x} may be a set of (μ⊗μ-measure zero. The present note describes a class of linear operators acting on a Banach function space X which forms a lattice ideal of operators on X, rather than an operator ideal, but coincides with the collection of hermitian positive trace class operators in the case of X=L2(μ.
Energy Technology Data Exchange (ETDEWEB)
Kagan, Yu.; Kikoin, K.A.; Mishchenko, A.S. [RRC Kurchatov Inst., Moscow (Russian Federation). Super Conductivity and Solid State
1997-02-01
On the grounds of the microscopic theory of heavy-fermion spin liquids a novel description of low-energy excitation spectra in CeNiSn and related compounds is offered. The anomalous properties of orthorhombic CeNiSn and related materials are explained by the interplay between the fermi-type spinon excitations with the energy scale T{sup *} {approx} T{sub K} and the one-site crystal field excitations with the energy {Delta}{sub CF} < T{sup *}. The theory gives both quantitative and qualitative description of inelastic neutron scattering spectra and low-temperature thermodynamics. It resolves also the apparent contradiction between metallic conductivity and gap-wise behavior of thermodynamic properties and spin response at low temperatures. (orig.). 8 refs.
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.
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.
Seon, C R; Choi, S H; Cheon, M S; Pak, S; Lee, H G; Biel, W; Barnsley, R
2010-10-01
A vacuum ultraviolet (VUV) spectrometer of a five-channel spectral system is designed for ITER main plasma impurity measurement. To develop and verify the system design, a two-channel prototype system is fabricated with No. 3 (14.4-31.8 nm) and No. 4 (29.0-60.0 nm) among the five channels. The optical system consists of a collimating mirror to collect the light from source to slit, two holographic diffraction gratings with toroidal geometry, and two different electronic detectors. For the test of the prototype system, a hollow cathode lamp is used as a light source. To find the appropriate detector for ITER VUV system, two kinds of detectors of the back-illuminated charge-coupled device and the microchannel plate electron multiplier are tested, and their performance has been investigated.
Qiu, Li; Shi, Yang; Yao, Fengqi; Xu, Gang; Xu, Bugong
2015-08-01
This paper focuses on the robust output feedback H₂/H∞ control issue for a class of discrete-time networked control systems with uncertain parameters and external disturbance. Sensor-to-controller and controller-to-actuator packet dropouts and time delays are considered simultaneously. According to the stochastic characteristic of the packet dropouts and time delays, a model based on a Markov jump system framework is proposed to randomly compensate for the adverse effect of the two-channel packet dropouts and time delays. To analyze the robust stability of the resulting closed-loop system, a Lyapunov function is proposed, based on which sufficient conditions for the existence of the H₂/H∞ controller are derived in terms of linear matrix inequalities, ensuring robust stochastic stability as well as the prescribed H₂ and H∞ performance. Finally, an angular positioning system is exploited to demonstrate the effectiveness and applicability of the proposed design strategy.
Lattice radial quantization by cubature
Neuberger, Herbert
2014-01-01
Basic aspects of a program to put field theories quantized in radial coordinates on the lattice are presented. Only scalar fields are discussed. Simple examples are solved to illustrate the strategy when applied to the 3D Ising model.
Wilby, Brian
1974-01-01
As an alternative to the usual method of counting squares to find the area of a plane shape, a method of counting lattice points (determined by vertices of a unit square) is proposed. Activities using this method are suggested. (DT)
De Soto, F; Carbonell, J; Leroy, J P; Pène, O; Roiesnel, C; Boucaud, Ph.
2007-01-01
We present the first results of a quantum field approach to nuclear models obtained by lattice techniques. Renormalization effects for fermion mass and coupling constant in case of scalar and pseudoscalar interaction lagrangian densities are discussed.
Ikezoe, R.; Ichimura, M.; Okada, T.; Itagaki, J.; Hirata, M.; Sumida, S.; Jang, S.; Izumi, K.; Tanaka, A.; Yoshikawa, M.; Kohagura, J.; Sakamoto, M.; Nakashima, Y.
2017-03-01
A two-channel microwave reflectometer system with fast microwave antenna switching capability was developed and applied to the GAMMA 10 tandem mirror device to study high-frequency small-amplitude fluctuations in a hot mirror plasma. The fast switching of the antennas is controlled using PIN diode switches, which offers the significant advantage of reducing the number of high-cost microwave components and digitizers with high bandwidths and large memory that are required to measure the spatiotemporal behavior of the high-frequency fluctuations. The use of two channels rather than one adds the important function of a simultaneous two-point measurement in either the radial direction or the direction of the antenna array to measure the phase profile of the fluctuations along with the normal amplitude profile. The density fluctuations measured using this system clearly showed the high-frequency coherent fluctuations that are associated with Alfvén-ion-cyclotron (AIC) waves in GAMMA 10. A correlation analysis applied to simultaneously measured density fluctuations showed that the phase component that was included in a reflected microwave provided both high coherence and a clear phase difference for the AIC waves, while the amplitude component showed neither significant coherence nor clear phase difference. The axial phase differences of the AIC waves measured inside the hot plasma confirmed the formation of a standing wave structure. The axial variation of the radial profiles was evaluated and a clear difference was found among the AIC waves for the first time, which would be a key to clarify the unknown boundary conditions of the AIC waves.
Baryon spectroscopy in lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Derek B. Leinweber; Wolodymyr Melnitchouk; David Richards; Anthony G. Williams; James Zanotti
2004-04-01
We review recent developments in the study of excited baryon spectroscopy in lattice QCD. After introducing the basic methods used to extract masses from correlation functions, we discuss various interpolating fields and lattice actions commonly used in the literature. We present a survey of results of recent calculations of excited baryons in quenched QCD, and outline possible future directions in the study of baryon spectra.
Lattice QCD: A Brief Introduction
Meyer, H. B.
A general introduction to lattice QCD is given. The reader is assumed to have some basic familiarity with the path integral representation of quantum field theory. Emphasis is placed on showing that the lattice regularization provides a robust conceptual and computational framework within quantum field theory. The goal is to provide a useful overview, with many references pointing to the following chapters and to freely available lecture series for more in-depth treatments of specifics topics.
Yamamoto, Arata
2016-01-01
We propose the lattice QCD calculation of the Berry phase which is defined by the ground state of a single fermion. We perform the ground-state projection of a single-fermion propagator, construct the Berry link variable on a momentum-space lattice, and calculate the Berry phase. As the first application, the first Chern number of the (2+1)-dimensional Wilson fermion is calculated by the Monte Carlo simulation.
Transport in Sawtooth photonic lattices
Weimann, Steffen; Real, Bastián; Cantillano, Camilo; Szameit, Alexander; Vicencio, Rodrigo A
2016-01-01
We investigate, theoretically and experimentally, a photonic realization of a Sawtooth lattice. This special lattice exhibits two spectral bands, with one of them experiencing a complete collapse to a highly degenerate flat band for a special set of inter-site coupling constants. We report the ob- servation of different transport regimes, including strong transport inhibition due to the appearance of the non-diffractive flat band. Moreover, we excite localized Shockley surfaces states, residing in the gap between the two linear bands.
Lattice Studies of Hyperon Spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Richards, David G. [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
2016-04-01
I describe recent progress at studying the spectrum of hadrons containing the strange quark through lattice QCD calculations. I emphasise in particular the richness of the spectrum revealed by lattice studies, with a spectrum of states at least as rich as that of the quark model. I conclude by prospects for future calculations, including in particular the determination of the decay amplitudes for the excited states.
Energy Technology Data Exchange (ETDEWEB)
DeGrand, T. [Univ. of Colorado, Boulder, CO (United States). Dept. of Physics
1997-06-01
These lectures provide an introduction to lattice methods for nonperturbative studies of Quantum Chromodynamics. Lecture 1: Basic techniques for QCD and results for hadron spectroscopy using the simplest discretizations; lecture 2: Improved actions--what they are and how well they work; lecture 3: SLAC physics from the lattice-structure functions, the mass of the glueball, heavy quarks and {alpha}{sub s} (M{sub z}), and B-{anti B} mixing. 67 refs., 36 figs.
Multifractal behaviour of -simplex lattic
Indian Academy of Sciences (India)
Sanjay Kumar; Debaprasad Giri; Sujata Krishna
2000-06-01
We study the asymptotic behaviour of resistance scaling and ﬂuctuation of resistance that give rise to ﬂicker noise in an -simplex lattice. We propose a simple method to calculate the resistance scaling and give a closed-form formula to calculate the exponent, , associated with resistance scaling, for any . Using current cumulant method we calculate the exact noise exponent for -simplex lattices.
Optimal lattice-structured materials
Messner, Mark C.
2016-11-01
This work describes a method for optimizing the mesostructure of lattice-structured materials. These materials are periodic arrays of slender members resembling efficient, lightweight macroscale structures like bridges and frame buildings. Current additive manufacturing technologies can assemble lattice structures with length scales ranging from nanometers to millimeters. Previous work demonstrates that lattice materials have excellent stiffness- and strength-to-weight scaling, outperforming natural materials. However, there are currently no methods for producing optimal mesostructures that consider the full space of possible 3D lattice topologies. The inverse homogenization approach for optimizing the periodic structure of lattice materials requires a parameterized, homogenized material model describing the response of an arbitrary structure. This work develops such a model, starting with a method for describing the long-wavelength, macroscale deformation of an arbitrary lattice. The work combines the homogenized model with a parameterized description of the total design space to generate a parameterized model. Finally, the work describes an optimization method capable of producing optimal mesostructures. Several examples demonstrate the optimization method. One of these examples produces an elastically isotropic, maximally stiff structure, here called the isotruss, that arguably outperforms the anisotropic octet truss topology.
Advances in Lattice Quantum Chromodynamics
McGlynn, Greg
In this thesis we make four contributions to the state of the art in numerical lattice simulations of quantum chromodynamics (QCD). First, we present the most detailed investigation yet of the autocorrelations of topological observations in hybrid Monte Carlo simulations of QCD and of the effects of the boundary conditions on these autocorrelations. This results in a numerical criterion for deciding when open boundary conditions are useful for reducing these autocorrelations, which are a major barrier to reliable calculations at fine lattice spacings. Second, we develop a dislocation-enhancing determinant, and demonstrate that it reduces the autocorrelation time of the topological charge. This alleviates problems with slow topological tunneling at fine lattice spacings, enabling simulations on fine lattices to be completed with much less computational effort. Third, we show how to apply the recently developed zMobius technique to hybrid Monte Carlo evolutions with domain wall fermions, achieving nearly a factor of two speedup in the light quark determinant, the single most expensive part of the calculation. The dislocation-enhancing determinant and the zMobius technique have enabled us to begin simulations of fine ensembles with four flavors of dynamical domain wall quarks. Finally, we show how to include the previously-neglected G1 operator in nonperturbative renormalization of the DeltaS = 1 effective weak Hamiltonian on the lattice. This removes an important systematic error in lattice calculations of weak matrix elements, in particular the important K → pipi decay.
Spin-glass, antiferromagnetism and Kondo behavior in Ce2Au1-CoSi3 alloys
Indian Academy of Sciences (India)
Subham Majumdar; E V Sampathkumaran; St Berger; M Della Mea; H Michor; E Bauer; M Brando; J Hemberger; A Loidl
2002-05-01
Recently, the solid solution Ce2Au1-CoSi3 has been shown to exhibit many magnetic anomalies associated with the competition between magnetic ordering and the Kondo effect. Here we report high pressure electrical resistivity of Ce2AuSi3, ac susceptibility () 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 maximum in Doniach’s magnetic phase diagram. The ac data reveal that there are in fact two magnetic transitions, one at 2 K and the other at 3 K for this compound, both of which are spin-glass-like. However, as the Co concentration is increased, antiferromagnetism is stabilized for intermediate compositions before attaining non-magnetism for the Co end member.
Single-crystalline study of the ferromagnetic kondo compound UCu{sub 0.9}Sb{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Bukowski, Z. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 WrocIaw (Poland); Troc, R. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 WrocIaw (Poland); Stepien-Damm, J. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 WrocIaw (Poland); SuIkowski, C. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 WrocIaw (Poland); Tran, V.H. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 WrocIaw (Poland)]. E-mail: V.H.Tran@int.pan.wroc.pl
2005-11-10
Single crystals of UCu{sub 0.9}Sb{sub 2} have been grown using the self-flux method and studied by means of X-ray diffraction, magnetic and electrical transport measurements. This compound crystallizes in a tetragonal structure of the HfCuSi{sub 2}-type (space group P4/nmm) and orders ferromagnetically below T {sub C} = 113 K with the easy-magnetization direction along the c-axis exhibiting a large magnetocrystalline anisotropy in both the ordered and paramagnetic states. The electrical resistivity, magnetoresistivity and thermoelectric power data are also given. A Kondo-like behaviour of the resistivity in the paramagnetic state is reported.
High pressure studies on the ferromagnetic dense Kondo systems CeRh3B2 and UCu2Ge2
Cornelius, A. L.; Schilling, J. S.; Endstra, T.; Mydosh, J. A.
1994-07-01
The dependence of the Curie temperature of the anomalous ferromagnets UCu2Ge2 and CeRh3B2 on hydrostatic pressure to 11 GPa is determined using a diamond-anvil cell loaded with dense helium as pressure medium. A sensitive primary/secondary coil system allows the detection of the ferromagnetic transition in the ac susceptibility for tiny samples with less than 1 μ mass. The Curie temperatures of the above two compounds, Tc≊110 K and 118 K, both increase initially under pressure but pass through maxima at 8 GPa and 2 GPa, respectively, before falling rapidly at higher pressures. We take this as evidence that both compounds behave as dense Kondo system, where Tc depends on the exchange coupling J according to a magnetic phase diagram originally proposed by Doniach.
A lexicographic shellability characterization of geometric lattices
Davidson, Ruth
2011-01-01
Geometric lattices are characterized as those finite, atomic lattices such that every atom ordering induces a lexicographic shelling given by an edge labeling known as a minimal labeling. This new characterization fits into a similar paradigm as McNamara's characterization of supersolvable lattices as those lattices admitting a different type of lexicographic shelling, namely one in which each maximal chain is labeled with a permutation of {1,...,n}. Geometric lattices arise as the intersection lattices of central hyperplane arrangements and more generally as the lattices of flats for matroids.
Embedded Lattice and Properties of Gram Matrix
Directory of Open Access Journals (Sweden)
Futa Yuichi
2017-03-01
Full Text Available In this article, we formalize in Mizar [14] the definition of embedding of lattice and its properties. We formally define an inner product on an embedded module. We also formalize properties of Gram matrix. We formally prove that an inverse of Gram matrix for a rational lattice exists. Lattice of Z-module is necessary for lattice problems, LLL (Lenstra, Lenstra and Lov´asz base reduction algorithm [16] and cryptographic systems with lattice [17].
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)
Lattice dislocation in Si nanowires
Energy Technology Data Exchange (ETDEWEB)
Omar, M.S., E-mail: dr_m_s_omar@yahoo.co [Department of Physics, College of Science, University of Salahaddin, Arbil, Iraqi Kurdistan (Iraq); Taha, H.T. [Department of Physics, College of Science, University of Salahaddin, Arbil, Iraqi Kurdistan (Iraq)
2009-12-15
Modified formulas were used to calculate lattice thermal expansion, specific heat and Bulk modulus for Si nanowires with diameters of 115, 56, 37 and 22 nm. From these values and Gruneisen parameter taken from reference, mean lattice volumes were found to be as 20.03 A{sup 3} for the bulk and 23.63, 29.91, 34.69 and 40.46 A{sup 3} for Si nanowire diameters mentioned above, respectively. Their mean bonding length was calculated to be as 0.235 nm for the bulk and 0.248, 0.269, 0.282 and 0.297 nm for the nanowires diameter mentioned above, respectively. By dividing the nanowires diameter on the mean bonding length, number of layers per each nanowire size was found to be as 230, 104, 65 and 37 for the diameters mentioned above, respectively. Lattice dislocations in 22 nm diameter wire were found to be from 0.00324 nm for the 1st central lattice to 0.2579 nm for the last surface lattice. Such dislocation was smaller for larger wire diameters. Dislocation concentration found to change in Si nanowires according to the proportionalities of surface thickness to nanowire radius ratios.
Hamiltonian tomography of photonic lattices
Ma, Ruichao; Owens, Clai; LaChapelle, Aman; Schuster, David I.; Simon, Jonathan
2017-06-01
In this paper we introduce an approach to Hamiltonian tomography of noninteracting tight-binding photonic lattices. To begin with, we prove that the matrix element of the low-energy effective Hamiltonian between sites α and β may be obtained directly from Sα β(ω ) , the (suitably normalized) two-port measurement between sites α and β at frequency ω . This general result enables complete characterization of both on-site energies and tunneling matrix elements in arbitrary lattice networks by spectroscopy, and suggests that coupling between lattice sites is a topological property of the two-port spectrum. We further provide extensions of this technique for measurement of band projectors in finite, disordered systems with good band flatness ratios, and apply the tool to direct real-space measurement of the Chern number. Our approach demonstrates the extraordinary potential of microwave quantum circuits for exploration of exotic synthetic materials, providing a clear path to characterization and control of single-particle properties of Jaynes-Cummings-Hubbard lattices. More broadly, we provide a robust, unified method of spectroscopic characterization of linear networks from photonic crystals to microwave lattices and everything in between.
Hydrodynamic behaviour of Lattice Boltzmann and Lattice BGK models
Behrend, O; Warren, P
1993-01-01
Abstract: We present a numerical analysis of the validity of classical and generalized hydrodynamics for Lattice Boltzmann Equation (LBE) and Lattice BGK methods in two and three dimensions, as a function of the collision parameters of these models. Our analysis is based on the wave-number dependence of the evolution operator. Good ranges of validity are found for BGK models as long as the relaxation time is chosen smaller than or equal to unity. The additional freedom in the choice of collision parameters for LBE models does not seem to give significant improvement.
Zhong, Yin; Liu, Yu; Luo, Hong-Gang
2017-10-01
The periodic Anderson model (PAM), where local electron orbitals interplay with itinerant electronic carriers, plays an essential role in our understanding of heavy fermion materials. Motivated by recent proposals for simulating the Kondo lattice model (KLM) in terms of alkaline-earth metal atoms, we take another step toward the simulation of PAM, which includes the crucial charge/valence fluctuation of local f-electrons beyond purely low-energy spin fluctuation in the KLM. To realize PAM, a transition induced by a suitable laser between the electronic excited and ground state of alkaline-earth metal atoms (1 S 0⇌3 P 0) is introduced. This leads to effective hybridization between local electrons and conduction electrons in PAM. Generally, the SU( N) version of PAM can be realized by our proposal, which gives a unique opportunity to detect large- N physics without complexity in realistic materials. In the present work, high-temperature physical features of standard [ SU(2)] PAM with harmonic trapping potential are analyzed by quantum Monte Carlo and dynamic mean-field theory, where the Mott/orbital-selective Mott state was found to coexist with metallic states. Indications for near-future experiments are provided. We expect our theoretical proposal and (hopefully) forthcoming experiments will deepen our understanding of heavy fermion systems. At the same time, we hope these will trigger further studies on related Mott physics, quantum criticality, and non-trivial topology in both the inhomogeneous and nonequilibrium realms.
Energy Technology Data Exchange (ETDEWEB)
Nguyen Bich Ha [Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Cau Giay Dist., Hanoi (Viet Nam); Nguyen Van Hop [Hanoi National University of Education, Hanoi (Viet Nam)], E-mail: bichha@iop.vast.ac.vn
2009-09-01
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.
Energy Technology Data Exchange (ETDEWEB)
Wegewijs, Maarten R [Institut fuer Theoretische Physik-Lehrstuhl A, RWTH Aachen, 52056 Aachen (Germany); Romeike, Christian [Institut fuer Theoretische Physik-Lehrstuhl A, RWTH Aachen, 52056 Aachen (Germany); Schoeller, Herbert [Institut fuer Theoretische Physik-Lehrstuhl A, RWTH Aachen, 52056 Aachen (Germany); Hofstetter, Walter [Institut fuer Theoretische Physik, J W Goethe-Universitaet Frankfurt, 60438 Frankfurt (Germany)
2007-09-15
We theoretically analyse coherent electron transport through a single-molecule magnet (SMM) in the regime where charge fluctuations are suppressed. Using the numerical renormalization group (NRG) technique, we calculate the low-temperature conductance as a function of the SMMs magnetic anisotropy parameters and the strength and orientation of an external magnetic field. We show how the microscopic magnetic symmetry of the molecule affects the transport via a Kondo effect with non-trivial dependence on a longitudinal field. In addition, we show how Berry's phase and the Kondo effect, both associated with reversal of the SMMs spin, appear when both the magnetic field amplitude and direction are varied. It is shown that both effects involve the magnetic excitations of the SMM in an essential way.
Nuclear Reactions from Lattice QCD
Briceño, Raúl A; Luu, Thomas C
2014-01-01
One of the overarching goals of nuclear physics is to rigorously compute properties of hadronic systems directly from the fundamental theory of strong interactions, Quantum Chromodynamics (QCD). In particular, the hope is to perform reliable calculations of nuclear reactions which will impact our understanding of environments that occur during big bang nucleosynthesis, the evolution of stars and supernovae, and within nuclear reactors and high energy/density facilities. Such calculations, being truly ab initio, would include all two-nucleon and three- nucleon (and higher) interactions in a consistent manner. Currently, lattice QCD provides the only reliable option for performing calculations of some of the low- energy hadronic observables. With the aim of bridging the gap between lattice QCD and nuclear many-body physics, the Institute for Nuclear Theory held a workshop on Nuclear Reactions from Lattice QCD on March 2013. In this review article, we report on the topics discussed in this workshop and the path ...
Quantum Gravity on the Lattice
Hamber, Herbert W
2009-01-01
I review the lattice approach to quantum gravity, and how it relates to the non-trivial ultraviolet fixed point scenario of the continuum theory. After a brief introduction covering the general problem of ultraviolet divergences in gravity and other non-renormalizable theories, I cover the general methods and goals of the lattice approach. An underlying theme is an attempt at establishing connections between the continuum renormalization group results, which are mainly based on diagrammatic perturbation theory, and the recent lattice results, which should apply to the strong gravity regime and are inherently non-perturbative. A second theme in this review is the ever-present natural correspondence between infrared methods of strongly coupled non-abelian gauge theories on the one hand, and the low energy approach to quantum gravity based on the renormalization group and universality of critical behavior on the other. Towards the end of the review I discuss possible observational consequences of path integral q...
Algebraic Lattices in QFT Renormalization
Borinsky, Michael
2016-07-01
The structure of overlapping subdivergences, which appear in the perturbative expansions of quantum field theory, is analyzed using algebraic lattice theory. It is shown that for specific QFTs the sets of subdivergences of Feynman diagrams form algebraic lattices. This class of QFTs includes the standard model. In kinematic renormalization schemes, in which tadpole diagrams vanish, these lattices are semimodular. This implies that the Hopf algebra of Feynman diagrams is graded by the coradical degree or equivalently that every maximal forest has the same length in the scope of BPHZ renormalization. As an application of this framework, a formula for the counter terms in zero-dimensional QFT is given together with some examples of the enumeration of primitive or skeleton diagrams.
Lattice Structures For Aerospace Applications
Del Olmo, E.; Grande, E.; Samartin, C. R.; Bezdenejnykh, M.; Torres, J.; Blanco, N.; Frovel, M.; Canas, J.
2012-07-01
The way of mass reduction improving performances in the aerospace structures is a constant and relevant challenge in the space business. The designs, materials and manufacturing processes are permanently in evolution to explore and get mass optimization solutions at low cost. In the framework of ICARO project, EADS CASA ESPACIO (ECE) has designed, manufactured and tested a technology demonstrator which shows that lattice type of grid structures is a promising weight saving solution for replacing some traditional metallic and composite structures for space applications. A virtual testing methodology was used in order to support the design of a high modulus CFRP cylindrical lattice technology demonstrator. The manufacturing process, based on composite Automatic Fiber Placement (AFP) technology developed by ECE, allows obtaining high quality low weight lattice structures potentially applicable to a wide range of aerospace structures. Launcher payload adaptors, satellite platforms, antenna towers or instrument supports are some promising candidates.
Kaon fluctuations from lattice QCD
Noronha-Hostler, Jacquelyn; Gunther, Jana; Parotto, Paolo; Pasztor, Attila; Vazquez, Israel Portillo; Ratti, Claudia
2016-01-01
We show that it is possible to isolate a set of kaon fluctuations in lattice QCD. By means of the Hadron Resonance Gas (HRG) model, we calculate the actual kaon second-to-first fluctuation ratio, which receives contribution from primordial kaons and resonance decays, and show that it is very close to the one obtained for primordial kaons in the Boltzmann approximation. The latter only involves the strangeness and electric charge chemical potentials, which are functions of $T$ and $\\mu_B$ due to the experimental constraint on strangeness and electric charge, and can therefore be calculated on the lattice. This provides an unambiguous method to extract the kaon freeze-out temperature, by comparing the lattice results to the experimental values for the corresponding fluctuations.
Hadron Structure on the Lattice
Can, K. U.; Kusno, A.; Mastropas, E. V.; Zanotti, J. M.
The aim of these lectures will be to provide an introduction to some of the concepts needed to study the structure of hadrons on the lattice. Topics covered include the electromagnetic form factors of the nucleon and pion, the nucleon's axial charge and moments of parton and generalised parton distribution functions. These are placed in a phenomenological context by describing how they can lead to insights into the distribution of charge, spin and momentum amongst a hadron's partonic constituents. We discuss the techniques required for extracting the relevant matrix elements from lattice simulations and draw attention to potential sources of systematic error. Examples of recent lattice results are presented and are compared with results from both experiment and theoretical models.
Flavor Physics and Lattice QCD
Bouchard, C M
2013-01-01
Our ability to resolve new physics effects is, largely, limited by the precision with which we calculate. The calculation of observables in the Standard (or a new physics) Model requires knowledge of associated hadronic contributions. The precision of such calculations, and therefore our ability to leverage experiment, is typically limited by hadronic uncertainties. The only first-principles method for calculating the nonperturbative, hadronic contributions is lattice QCD. Modern lattice calculations have controlled errors, are systematically improvable, and in some cases, are pushing the sub-percent level of precision. I outline the role played by, highlight state of the art efforts in, and discuss possible future directions of lattice calculations in flavor physics.
Lattice QCD for nuclear physics
Meyer, Harvey
2015-01-01
With ever increasing computational resources and improvements in algorithms, new opportunities are emerging for lattice gauge theory to address key questions in strongly interacting systems, such as nuclear matter. Calculations today use dynamical gauge-field ensembles with degenerate light up/down quarks and the strange quark and it is possible now to consider including charm-quark degrees of freedom in the QCD vacuum. Pion masses and other sources of systematic error, such as finite-volume and discretization effects, are beginning to be quantified systematically. Altogether, an era of precision calculation has begun, and many new observables will be calculated at the new computational facilities. The aim of this set of lectures is to provide graduate students with a grounding in the application of lattice gauge theory methods to strongly interacting systems, and in particular to nuclear physics. A wide variety of topics are covered, including continuum field theory, lattice discretizations, hadron spect...
Nucleon structure from lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Dinter, Simon
2012-11-13
In this thesis we compute within lattice QCD observables related to the structure of the nucleon. One part of this thesis is concerned with moments of parton distribution functions (PDFs). Those moments are essential elements for the understanding of nucleon structure and can be extracted from a global analysis of deep inelastic scattering experiments. On the theoretical side they can be computed non-perturbatively by means of lattice QCD. However, since the time lattice calculations of moments of PDFs are available, there is a tension between these lattice calculations and the results from a global analysis of experimental data. We examine whether systematic effects are responsible for this tension, and study particularly intensively the effects of excited states by a dedicated high precision computation. Moreover, we carry out a first computation with four dynamical flavors. Another aspect of this thesis is a feasibility study of a lattice QCD computation of the scalar quark content of the nucleon, which is an important element in the cross-section of a heavy particle with the nucleon mediated by a scalar particle (e.g. Higgs particle) and can therefore have an impact on Dark Matter searches. Existing lattice QCD calculations of this quantity usually have a large error and thus a low significance for phenomenological applications. We use a variance-reduction technique for quark-disconnected diagrams to obtain a precise result. Furthermore, we introduce a new stochastic method for the calculation of connected 3-point correlation functions, which are needed to compute nucleon structure observables, as an alternative to the usual sequential propagator method. In an explorative study we check whether this new method is competitive to the standard one. We use Wilson twisted mass fermions at maximal twist in all our calculations, such that all observables considered here have only O(a{sup 2}) discretization effects.
Indications of a Quantum Critical Point in Bi2Sr2CaCu2O8+δ Using a Local Kondo Effect
Calleja, Eduardo; Dai, Jixia; Arnold, Gerald; Gu, Genda; McElroy, Kyle
2014-03-01
A complete understanding of the complex phase diagrams that are present in high temperature superconductors remains elusive. While there is an overwhelming amount of experimental data on the existence and interplay of the phases present in high Tc superconductors from local probes, much of the existing data only looks at the charge degree of freedom of the material. By substituting Fe atoms for Cu atoms in the CuO plane of Bi2Sr2CaCu2O8+δ (Bi2212), we gain the ability to access the spin degree of freedom since the Fe atoms retain their magnetization below the superconducting transition temperature. This leads to a local Kondo effect which can be observed using Spectroscopic-Imaging Scanning Tunneling Microscopy (SI-STM) and the local Kondo temperature can be extracted from spectra via a theoretical model. We show that the examination of this local Kondo temperature across local and sample average doping leads to the observation of a change in the quasiparticle spin degree of freedom at a quantum critical point (QCP) with a nominal hole doping of roughly 0.22, in agreement with other probes. The observation of the QCP in Bi2212 with this new method to access the spin degree of freedom helps to unravel some of the mystery behind the complex phase diagram of Bi2212.
Nuclear Physics from Lattice QCD
Energy Technology Data Exchange (ETDEWEB)
William Detmold, Silas Beane, Konstantinos Orginos, Martin Savage
2011-01-01
We review recent progress toward establishing lattice Quantum Chromodynamics as a predictive calculational framework for nuclear physics. A survey of the current techniques that are used to extract low-energy hadronic scattering amplitudes and interactions is followed by a review of recent two-body and few-body calculations by the NPLQCD collaboration and others. An outline of the nuclear physics that is expected to be accomplished with Lattice QCD in the next decade, along with estimates of the required computational resources, is presented.
Chiral Fermions on the Lattice
Bietenholz, Wolfgang
2010-01-01
In the last century the non-perturbative regularization of chiral fermions was a long-standing problem. We review how this problem was finally overcome by the formulation of a modified but exact form of chiral symmetry on the lattice. This also provides a sound definition of the topological charge of lattice gauge configurations. We illustrate a variety of applications to QCD in the p-, the epsilon- and the delta-regime, where simulation results can now be related to Random Matrix Theory and Chiral Perturbation Theory. The latter contains Low Energy Constants as free parameters, and we comment on their evaluation from first principles of QCD.
Lattices, graphs, and Conway mutation
Greene, Joshua Evan
2011-01-01
The d-invariant of an integral, positive definite lattice L records the minimal norm of a characteristic covector in each equivalence class mod 2L. We prove that the 2-isomorphism type of a connected graph is determined by the d-invariant of its lattice of integral cuts (or flows). As an application, we prove that a reduced, alternating link diagram is determined up to mutation by the Heegaard Floer homology of the link's branched double-cover. Thus, alternating links with homeomorphic branched double-covers are mutants.
Graphene on graphene antidot lattices
DEFF Research Database (Denmark)
Gregersen, Søren Schou; Pedersen, Jesper Goor; Power, Stephen
2015-01-01
Graphene bilayer systems are known to exhibit a band gap when the layer symmetry is broken by applying a perpendicular electric field. The resulting band structure resembles that of a conventional semiconductor with a parabolic dispersion. Here, we introduce a bilayer graphene heterostructure......, where single-layer graphene is placed on top of another layer of graphene with a regular lattice of antidots. We dub this class of graphene systems GOAL: graphene on graphene antidot lattice. By varying the structure geometry, band-structure engineering can be performed to obtain linearly dispersing...
Unconventional superconductivity in honeycomb lattice
Directory of Open Access Journals (Sweden)
P Sahebsara
2013-03-01
Full Text Available The possibility of symmetrical s-wave superconductivity in the honeycomb lattice is studied within a strongly correlated regime, using the Hubbard model. The superconducting order parameter is defined by introducing the Green function, which is obtained by calculating the density of the electrons . In this study showed that the superconducting order parameter appears in doping interval between 0 and 0.5, and x=0.25 is the optimum doping for the s-wave superconductivity in honeycomb lattice.
Directory of Open Access Journals (Sweden)
Carlos Alberto Nigro
2012-01-01
Full Text Available Objective. To evaluate the accuracy and reliability of the medical decision based on the results of the hand scoring from a two-channel recording device (ApneaLink plus clinical data for the prescription of a CPAP assay in patients with suspected OSA. Methods. 39 subjects were assessed in the sleep laboratory with polysomnography and ApneaLink. The patients completed the Epworth sleepiness scale and a clinical history. Two blinded independent observers decided to prescribe CPAP according to the results of the PSG (gold standard, observer A, ApneaLink (alternative method, observer B, and the clinical parameters. Sensitivity and specificity of observer B on the indication of CPAP were calculated. The interobserver agreement for the indication of CPAP was assessed using kappa statistics. Results. 38 subjects were included (26 men, mean age 47.5, mean RDI 28.7, mean BMI 31.4 kg/m2. The prevalence of OSA was 84%. The sensitivity and specificity of observer B to initiate a CPAP trial were 90.6% and 100%, respectively. The interrater agreement for the prescription of CPAP was good (kappa: 0.75. Conclusion. This study has shown that the use of ApneaLink plus clinical data has made it possible to indicate CPAP reliably in most patients with high-clinical pretest for OSA.
Pruthvi, Hemanth; Ramesh, K. B.
2015-06-01
One of the three planned back-end systems for the proposed National Large Solar Telescope (NLST) is the Solar Dynamics Imaging System (SDIS) which is intended to obtain near simultaneous images in multiple wavelengths. As a first step, a prototype system with two channel imaging has been developed and installed at the back-end of the White light Active Region Monitor (WARM) telescope at Kodaikanal Observatory. A two-mirror Coelostat serves as a light feeding system to a refracting objective while an optical breadboard serves as a platform for the back-end instruments. A re-imaging system is used before the prime focus to get two light channels for the observations in two wavelengths. The re-imaging system is designed using ZEMAX and the alignment of the system is done using a laser. Full disk images are obtained using a red filter (674.2nm/10nm) and a G-band filter (430.5nm/0.84nm). Design aspects of the re-imaging system, preliminary observations and image reduction methods are described in this paper.
Kapitanov, V A; Ponomarev, Yu N; Tyryshkin, I S; Rostov, A P
2007-04-01
We describe the hardware and software of the high-sensitive two-channel opto-acoustic spectrometer with a near infrared diode laser. A semiconductor TEC-100 laser with outer resonator generates a continuous single-frequency radiation in the range of 6040-6300 cm-1 with spectral resolution better that 10 MHz. The newly designed model of photo-acoustic cells in the form of a ring type resonator was used in the spectrometer, and the system allows the measurement of a weak absorption coefficient equal to 1.4x10(-7) cm-1 Hz-1/2 with a laser radiation power of 0.003 W. The methane absorption spectra within a range of 6080-6180 cm-1 were measured with a spectral resolution of 10 MHz and the signal to noise ratio more than 10(3). Six hundred absorption lines were recorded, which is twice as many as in HITRAN-2004. The accurate measurements of the half-width and shift of methane unresolved triplet R3 of 2nu3 band permit us to determine values of the broadening and shift coefficients for CH4-air, CH4-N2, and CH4-SF6 mixtures.
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
Hamiltonian monodromy as lattice defect
Zhilinskii, B.
2003-01-01
The analogy between monodromy in dynamical (Hamiltonian) systems and defects in crystal lattices is used in order to formulate some general conjectures about possible types of qualitative features of quantum systems which can be interpreted as a manifestation of classical monodromy in quantum finite particle (molecular) problems.
Triangles in a Lattice Parabola.
Sastry, K. R. S.
1991-01-01
Discussed are properties possessed by polygons inscribed in the lattice parabola y=x, including the area of a triangle, triangles of minimum area, conditions for right triangles, triangles whose area is the cube of an integer, and implications of Pick's Theorem. Further directions to pursue are suggested. (MDH)
Nucleon structure using lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Alexandrou, C.; Kallidonis, C. [Cyprus Univ., Nicosia (Cyprus). Dept. of Physics; The Cyprus Institute, Nicosia (Cyprus). Computational-Based Science and technology Research Center; Constantinou, M.; Hatziyiannakou, K. [Cyprus Univ., Nicosia (Cyprus). Dept. of Physics; Drach, V. [DESY Zeuthen (Germany). John von Neumann-Institut fuer Computing NIC; Jansen, K. [DESY Zeuthen (Germany). John von Neumann-Institut fuer Computing NIC; Cyprus Univ., Nicosia (Cyprus). Dept. of Physics; Koutsou, G.; Vaquero, A. [The Cyprus Institute, Nicosia (Cyprus). Computational-Based Science and technology Research Center; Leontiou, T. [Frederick Univ, Nicosia (Cyprus). General Dept.
2013-03-15
A review of recent nucleon structure calculations within lattice QCD is presented. The nucleon excited states, the axial charge, the isovector momentum fraction and helicity distribution are discussed, assessing the methods applied for their study, including approaches to evaluate the disconnected contributions. Results on the spin carried by the quarks in the nucleon are also presented.
Anisotropic dissipation in lattice metamaterials
Directory of Open Access Journals (Sweden)
Dimitri Krattiger
2016-12-01
Full Text Available Plane wave propagation in an elastic lattice material follows regular patterns as dictated by the nature of the lattice symmetry and the mechanical configuration of the unit cell. A unique feature pertains to the loss of elastodynamic isotropy at frequencies where the wavelength is on the order of the lattice spacing or shorter. Anisotropy may also be realized at lower frequencies with the inclusion of local resonators, especially when designed to exhibit directionally non-uniform connectivity and/or cross-sectional geometry. In this paper, we consider free and driven waves within a plate-like lattice−with and without local resonators−and examine the effects of damping on the isofrequency dispersion curves. We also examine, for free waves, the effects of damping on the frequency-dependent anisotropy of dissipation. Furthermore, we investigate the possibility of engineering the dissipation anisotropy by tuning the directional properties of the prescribed damping. The results demonstrate that uniformly applied damping tends to reduce the intensity of anisotropy in the isofrequency dispersion curves. On the other hand, lattice crystals and metamaterials are shown to provide an excellent platform for direction-dependent dissipation engineering which may be realized by simple changes in the spatial distribution of the damping elements.
Triangles in a Lattice Parabola.
Sastry, K. R. S.
1991-01-01
Discussed are properties possessed by polygons inscribed in the lattice parabola y=x, including the area of a triangle, triangles of minimum area, conditions for right triangles, triangles whose area is the cube of an integer, and implications of Pick's Theorem. Further directions to pursue are suggested. (MDH)
Lattice investigation of tetraquark candidates
Energy Technology Data Exchange (ETDEWEB)
Berlin, Joshua; Wagner, Marc [Goethe-Universitaet Frankfurt am Main, Institut fuer Theoretische Physik (Germany); Abdel-Rehim, Abdou; Alexandrou, Constantia; Gravina, Mario; Koutsou, Giannis [Department of Physics, University of Cyprus, Nicosia (Cyprus); Computation-based Science and Technology Research Center, Cyprus Institute, Nicosia (Cyprus); Dalla Brida, Mattia [School of Mathematics, Trinity College Dublin (Ireland)
2014-07-01
We present the status of an ongoing long-term lattice QCD project concerned with the study of light and heavy tetraquark candidates, using a variety of different creation operators. The computation of disconnected diagrams, which is technically challenging, is discussed in detail.
Decompressive craniectomy with lattice duraplasty.
Mitchell, P; Tseng, M; Mendelow, A D
2004-02-01
A method of opening dura for decompressive craniectomies is described. Numerous cuts intersecting in a lattice pattern allow the dura to expand in a gradual and controlled manner minimising the chances of cortical laceration or venous kinking on the craniectomy edge.
From lattice gases to polymers
Frenkel, D.
1990-01-01
The modification of a technique that was developed to study time correlations in lattice-gas cellular automata to facilitate the numerical simulation of chain molecules is described. As an example, the calculation of the excess chemical potential of an ideal polymer in a dense colloidal
Subwavelength vortical plasmonic lattice solitons.
Ye, Fangwei; Mihalache, Dumitru; Hu, Bambi; Panoiu, Nicolae C
2011-04-01
We present a theoretical study of vortical plasmonic lattice solitons, which form in two-dimensional arrays of metallic nanowires embedded into nonlinear media with both focusing and defocusing Kerr nonlinearities. Their existence, stability, and subwavelength spatial confinement are investigated in detail.
Beane, Silas
2009-01-01
Recent studies by the NPLQCD collaboration of hadronic interactions using lattice QCD are reviewed, with an emphasis on a recent calculation of meson-baryon scattering lengths. Ongoing high-statistics calculations of baryon interactions are also reviewed. In particular, new insights into the signal/noise problems that plague correlation functions involving baryons are discussed.
Hybrid Charmonium from Lattice QCD
Luo, X Q
2006-01-01
We review our recent results on the JPC = 0¡¡ exotic hybrid charmonium mass and JPC = 0¡+, 1¡¡ and 1++ nonexotic hybrid charmonium spectrum from anisotropic improved lattice QCD and discuss the relevance to the recent discovery of the Y(4260) state and future experimental search for other states.
Chiral fermions on the lattice
Jahn, O; Jahn, Oliver; Pawlowski, Jan M.
2002-01-01
We discuss topological obstructions to putting chiral fermions on an even dimensional lattice. The setting includes Ginsparg-Wilson fermions, but is more general. We prove a theorem which relates the total chirality to the difference of generalised winding numbers of chiral projection operators. For an odd number of Weyl fermions this implies that particles and anti-particles live in topologically different spaces.
Orbital optical lattices with bosons
Kock, T.; Hippler, C.; Ewerbeck, A.; Hemmerich, A.
2016-02-01
This article provides a synopsis of our recent experimental work exploring Bose-Einstein condensation in metastable higher Bloch bands of optical lattices. Bipartite lattice geometries have allowed us to implement appropriate band structures, which meet three basic requirements: the existence of metastable excited states sufficiently protected from collisional band relaxation, a mechanism to excite the atoms initially prepared in the lowest band with moderate entropy increase, and the possibility of cross-dimensional tunneling dynamics, necessary to establish coherence along all lattice axes. A variety of bands can be selectively populated and a subsequent thermalization process leads to the formation of a condensate in the lowest energy state of the chosen band. As examples the 2nd, 4th and 7th bands in a bipartite square lattice are discussed. The geometry of the 2nd and 7th bands can be tuned such that two inequivalent energetically degenerate energy minima arise at the X ±-points at the edge of the 1st Brillouin zone. In this case even a small interaction energy is sufficient to lock the phase between the two condensation points such that a complex-valued chiral superfluid order parameter can emerge, which breaks time reversal symmetry. In the 4th band a condensate can be formed at the Γ-point in the center of the 1st Brillouin zone, which can be used to explore topologically protected band touching points. The new techniques to access orbital degrees of freedom in higher bands greatly extend the class of many-body scenarios that can be explored with bosons in optical lattices.
Hadron Structure and Spectrum from the Lattice
Lang, C B
2015-01-01
Lattice calculations for hadrons are now entering the domain of resonances and scattering, necessitating a better understanding of the observed discrete energy spectrum. This is a reviewing survey about recent lattice QCD results, with some emphasis on spectrum and scattering.
Gauge Fixing on the Lattice without Ambiguity
Vink, Jeroen C; 10.1016/0370-2693(92)91372-G
2009-01-01
A new gauge fixing condition is discussed, which is (lattice) rotation invariant, has the `smoothness' properties of the Landau gauge but can be efficiently computed and is unambiguous for almost all lattice gauge field configurations.
Turbo Lattices: Construction and Performance Analysis
Sakzad, Amin; Panario, Daniel
2011-01-01
In this paper a new class of lattices called turbo lattices is introduced and established. We use the lattice Construction $D$ to produce turbo lattices. This method needs a set of nested linear codes as its underlying structure. We benefit from turbo codes as our basis codes. Therefore, a set of nested turbo codes based on nested interleavers and nested convolutional codes is built. To this end, we employ both tail-biting and zero-tail convolutional codes. Using these codes, along with construction $D$, turbo lattices are created. Several properties of Construction $D$ lattices and fundamental characteristics of turbo lattices including the minimum distance, coding gain, kissing number and an upper bound on the probability of error under a maximum likelihood decoder over AWGN channel are investigated. Furthermore, a multi-stage turbo lattice decoding algorithm based on iterative turbo decoding algorithm is given. Finally, simulation experiments provide strong agreement with our theoretical results. More prec...
Chiral Four-Dimensional Heterotic Covariant Lattices
Beye, Florian
2014-01-01
In the covariant lattice formalism, chiral four-dimensional heterotic string vacua are obtained from certain even self-dual lattices which completely decompose into a left-mover and a right-mover lattice. The main purpose of this work is to classify all right-mover lattices that can appear in such a chiral model, and to study the corresponding left-mover lattices using the theory of lattice genera. In particular, the Smith-Minkowski-Siegel mass formula is employed to calculate a lower bound on the number of left-mover lattices. Also, the known relationship between asymmetric orbifolds and covariant lattices is considered in the context of our classification.
Distributive lattice orderings and Priestley duality
Krebs, Michel
2007-01-01
The ordering relation of a bounded distributive lattice L is a (distributive) (0, 1)-sublattice of L \\times L. This construction gives rise to a functor \\Phi from the category of bounded distributive lattices to itself. We examine the interaction of \\Phi with Priestley duality and characterise those bounded distributive lattices L such that there is a bounded distributive lattice K such that \\Phi(K) is (isomorphic to) L.
Rough Class on a Completely Distributive Lattice
Institute of Scientific and Technical Information of China (English)
陈德刚; 张文修; 宋士吉
2003-01-01
This paper generalizes the Pawlak rough set method to a completely distributive lattice. Theconcept of a rough set has many applications in data mining. The approximation operators on a completelydistributive lattice are studied, the rough class on a completely distributive lattice is defined and theexpressional theorems of the rough class are proven. These expressional theorems are used to prove that thecollection of all rough classes is an atomic completely distributive lattice.
Jang, Kuk-In; Shim, Miseon; Lee, Sang Min; Huh, Hyu Jung; Huh, Seung; Joo, Ji-Young; Lee, Seung-Hwan; Chae, Jeong-Ho
2017-06-20
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.
Numerical renormalization group method for quantum impurity systems
Bulla, Ralf; Costi, Theo A.; Pruschke, Thomas
2008-04-01
In the early 1970s, Wilson developed the concept of a fully nonperturbative renormalization group transformation. When applied to the Kondo problem, this numerical renormalization group (NRG) method gave for the first time the full crossover from the high-temperature phase of a free spin to the low-temperature phase of a completely screened spin. The NRG method was later generalized to a variety of quantum impurity problems. The purpose of this review is to give a brief introduction to the NRG method, including some guidelines for calculating physical quantities, and to survey the development of the NRG method and its various applications over the last 30 years. These applications include variants of the original Kondo problem such as the non-Fermi-liquid behavior in the two-channel Kondo model, dissipative quantum systems such as the spin-boson model, and lattice systems in the framework of the dynamical mean-field theory.
Modified $U(1)$ lattice gauge theory towards realistic lattice QED
Bornyakov, V G; Müller-Preussker, M
1992-01-01
We study properties of the compact $~4D~$ $U(1)$ lattice gauge theory with monopoles {\\it removed}. Employing Monte Carlo simulations we calculate correlators of scalar, vector and tensor operators at zero and nonzero momenta $~\\vec{p}~$. We confirm that the theory without monopoles has no phase transition, at least, in the interval $~0 < \\beta \\leq 2~$. There the photon becomes massless and fits the lattice free field theory dispersion relation very well. The energies of the $~0^{++}~$, $~1^{+-}~$ and $~2^{++}~$ states show a rather weak dependence on the coupling in the interval of $~\\beta~$ investigated, and their ratios are practically constant. We show also a further modification of the theory suppressing the negative plaquettes to improve drastically the overlap with the lowest states (at least, for $~J=1$).
The Developement of A Lattice Structured Database
DEFF Research Database (Denmark)
Bruun, Hans
to a given set of inserted terms, that is the smallest lattice where the inserted terms preserve their value compared to the value in the initial algebra/lattice. The database is the dual representation of this most disjoint lattice. We develop algorithms to construct and make queries to the database....
Lattice Boltzmann solver of Rossler equation
Institute of Scientific and Technical Information of China (English)
GuangwuYAN; LiRUAN
2000-01-01
We proposed a lattice Boltzmann model for the Rossler equation. Using a method of multiscales in the lattice Boltzmann model, we get the diffusion reaction as a special case. If the diffusion effect disappeared, we can obtain the lattice Boltzmann solution of the Rossler equation on the mesescopic scale. The numerical results show the method can be used to simulate Rossler equation.
Clar sextets in square graphene antidot lattices
DEFF Research Database (Denmark)
Petersen, Rene; Pedersen, Thomas Garm; Jauho, Antti-Pekka
2011-01-01
A periodic array of holes transforms graphene from a semimetal into a semiconductor with a band gap tuneable by varying the parameters of the lattice. In earlier work only hexagonal lattices have been treated. Using atomistic models we here investigate the size of the band gap of a square lattice...
Modal analysis of kagome-lattice structures
Perez, H.; Blakley, S.; Zheltikov, A. M.
2015-05-01
The first few lowest order circularly symmetric electromagnetic eigenmodes of a full kagome lattice are compared to those of a kagome lattice with a hexagonal defect. This analysis offers important insights into the physics behind the waveguiding properties of hollow-core fibers with a kagome-lattice cladding.
Perfect and Quasi-Perfect Lattice Actions
Bietenholz, W
1998-01-01
Perfect lattice actions are exiting with several respects: they provide new insight into conceptual questions of the lattice regularization, and quasi-perfect actions could enable a great leap forward in the non-perturbative solution of QCD. We try to transmit a flavor of them, also beyond the lattice community.
DEFF Research Database (Denmark)
Fajstrup, Lisbeth
The set of d-structures on a topological space form a lattice and in fact a locale. There is a Galois connection between the lattice of subsets of the space and the lattice of d-structures. Variation of the d-structures induces change in the spaces of directed paths. Hence variation of d...
SIMPLE LATTICE BOLTZMANN MODEL FOR TRAFFIC FLOWS
Institute of Scientific and Technical Information of China (English)
Yan Guangwu; Hu Shouxin
2000-01-01
A lattice Boltzmann model with 5-bit lattice for traffic flows is proposed.Using the Chapman-Enskog expansion and multi-scale technique,we obtain the higher-order moments of equilibrium distribution function.A simple traffic light problem is simulated by using the present lattice Boltzmann model,and the result agrees well with analytical solution.
Exact Chiral Symmetry on the Lattice
Neuberger, H
2001-01-01
Developments during the last eight years have refuted the folklore that chiral symmetries cannot be preserved on the lattice. The mechanism that permits chiral symmetry to coexist with the lattice is quite general and may work in Nature as well. The reconciliation between chiral symmetry and the lattice is likely to revolutionize the field of numerical QCD.
Mayet-Godowski Hilbert Lattice Equations
Megill, Norman D.; Pavicic, Mladen
2006-01-01
Several new results in the field of Hilbert lattice equations based on states defined on the lattice as well as novel techniques used to arrive at these results are presented. An open problem of Mayet concerning Hilbert lattice equations based on Hilbert-space-valued states is answered.