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Anderson Model (anderson + model)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

Conductance of inhomogeneous systems: Real-time dynamics

ANNALEN DER PHYSIK, Issue 9 2010
A. Branschädel
Numerical time evolution of transport states using time dependent Density Matrix Renormalization Group (td-DMRG) methods has turned out to be a powerful tool to calculate the linear and finite bias conductance of interacting impurity systems coupled to non-interacting one-dimensional leads. Several models, including the Interacting Resonant Level Model (IRLM), the Single Impurity Anderson Model (SIAM), as well as models with different multi site structures, have been subject of investigations in this context. In this work we give an overview of the different numerical approaches that have been successfully applied to the problem and go into considerable detail when we comment on the techniques that have been used to obtain the full I,V-characteristics for the IRLM. Using a model of spinless fermions consisting of an extended interacting nanostructure attached to non-interacting leads, we explain the method we use to obtain the current,voltage characteristics and discuss the finite size effects that have to be taken into account. We report results for the linear and finite bias conductance through a seven site structure with weak and strong nearest-neighbor interactions. Comparison with exact diagonalisation results in the non-interacting limit serve as a verification of the accuracy of our approach. Finally we discuss the possibility of effectively enlarging the finite system by applying damped boundaries and give an estimate of the effective system size and accuracy that can be expected in this case. [source]

Single impurity Anderson model and band anti-crossing in the Ga1,xInx Ny As1,y material system

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2008
Nikolaos Vogiatzis
Abstract The role of the single-N impurity in the GaInNAs system is evaluated using the single impurity Anderson model. The N impurities can act either as scattering resonances or as bound states depending on their energy position. For the former case, using self-energy calculations and Matsubara Green's functions we investigate the nature of the mixed single-N state (energy broadening, shift). The effect of this interaction on the perturbed conduction subbands is also examined. The single impurity Anderson model results in a complex band structure. The real part of the band structure can be directly related to the dispersion obtained with the band anti-crossing model and is in very good agreement. The imaginary bandstructure contains further information about the mixing of the nitrogen state and the conduction band which is not contained within the band anti-crossing model. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Kondo effect in oscillating molecules

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2009
Jernej Mravlje
Abstract We consider electronic transport through break-junctions bridged by a single molecule in the Kondo regime. We describe the system by a two-channel Anderson model. We take the tunneling matrix elements to depend on the position of the molecule. It is shown, that if the modulation of the tunneling by displacement is large, the potential confining the molecule to the central position between the leads is softened and the position of the molecule is increasingly susceptible to external perturbations that break the inversion symmetry. In this regime, the molecule is attracted to one of the leads and as a consequence the conductance is small. We argue on semi-classical grounds why the softening occurs and corroborate our findings by numerical examples obtained by Wilson's numerical renormalization group and Schönhammer,Gunnarsson's variational method (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Spin-polarized charge transport through ionic clusters of magnetic oxides

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006
G. A. Gehring
Abstract We analyze the spin-controlled charge transfer through a heterostructure consisting of one octahedral and one tetrahedral iron,oxygen ionic clusters, which are site-coupled, sharing an oxygen ion. A number of charge carriers can be manipulated by valence-uncompensated doping. The electron-energy structure of the clusters and that of the heterostructure are found on the basis of the Anderson model. Current,voltage (I,V ) characteristics, derived from the Landauer-like formula, turn out to be highly sensitive to the position of the Fermi level. We also calculated the magnetoresistance for the heterostructure with different orientations of the magnetic field. The result confirmed the empirical data for Ca:YIG, which indicate strong anisotropy of the magnetoresistance. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Electron-electron relaxation in disordered interacting systems

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008
Peter Bozsoki
Abstract We study the relaxation of a non-equilibrium carrier distribution under the influence of the electron-electron interaction in the presence of disorder. Based on the Anderson model, our Hamiltonian is composed from a single particle part including the disorder and a two-particle part accounting for the Coulomb interaction. We apply the equation-of-motion approach for the density matrix, which provides a fully microscopic description of the relaxation. Our results show that the nonequilibrium distribution in this closed and internally interacting system relaxes exponentially fast during the initial dynamics. This fast relaxation can be described by a phenomenological damping rate. The total single particle energy decreases in the redistribution process, keeping the total energy of the system fixed. It turns out that the relaxation rate decreases with increasing disorder. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Local level statistics for optical and transport properties of disordered systems at finite temperature

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2006
A. Malyshev
Abstract It is argued that the (traditional) global level statistics which determines localization and coherent transport properties of disordered systems (e.g. the Anderson model) at zero temperature becomes inappropriate when it comes to incoherent transport. We define local level statistics which proves to be relevant for finite temperature incoherent transport and optics of one-dimensional systems (e.g. molecular aggregates, conjugated polymers, etc.). (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

On large-scale diagonalization techniques for the Anderson model of localization

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2007
Olaf Schenk
We propose efficient preconditioning algorithms for an eigenvalue problem arising in quantum physics, namely the computation of a few interior eigenvalues and their associated eigenvectors for large-scale sparse real and symmetric indefinite matrices of the Anderson model of localization. Our preconditioning approaches for the shift-and-invert symmetric indefinite linear system are based on maximum weighted matchings and algebraic multi-level incomplete LDLT factorizations. These techniques can be seen as a complement to the alternative idea of using more complete pivoting techniques for the highly ill-conditioned symmetric indefinite Anderson matrices. Our numerical examples reveal that recent algebraic multi-level preconditioning solvers can accelerate the computation of a large-scale eigenvalue problem corresponding to the Anderson model of localization by several orders of magnitude. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Conductance distribution at criticality: one-dimensional Anderson model with random long-range hopping

ANNALEN DER PHYSIK, Issue 12 2009
A. Méndez
Abstract We study numerically the conductance distribution function w(T) for the one-dimensional Anderson model with random long-range hopping described by the Power-law Banded Random Matrix model at criticality. We concentrate on the case of two single-channel leads attached to the system. We observe a smooth transition from localized to delocalized behavior in the conductance distribution by increasing b, the effective bandwidth of the model. Also, for b < 1 we show that w(ln T/Ttyp) is scale invariant, where Ttyp = exp , ln T , is the typical value of T. Moreover, we find that for T < Ttyp, w(ln T/Ttyp) shows a universal behavior proportional to (T/Ttyp) -1/2. [source]

Magnetic impurities in small metal clusters

ANNALEN DER PHYSIK, Issue 9-10 2005
G.M. Pastor
Abstract Magnetic impurities in small metallic clusters are investigated in the framework of the Anderson model by using exact diagonalization and geometry optimization methods. The singlet-triplet spin gap ,E shows a remarkable dependence as a function of band-filling, cluster structure, and impurity position that can be interpreted in terms of the environment-specific conduction-electron spectrum. The low-energy spin excitations involve similar energies as isomerizations. Interesting correlations between cluster structure and magnetic behavior are revealed. Finite-temperature properties such as specific heat, effective impurity moment, and magnetic susceptibility are calculated exactly in the canonical ensemble. A finite-size equivalent of the Kondo effect is identified and its structural dependence is discussed. [source]

A nonlinear theoretical model for prediction of mechanical behavior of particulate composites and experimental verification of the model predictions

POLYMER COMPOSITES, Issue 7 2010
A. Ramazani S.A.
A model for prediction the stress-strain behavior of particulate composite over wide ranges of filler concentration and composite deformation has been developed through combination of Anderson's and Yilmizer's model. The constitutive equations are extracted from first law of thermodynamic and nonlinear dilatational effects which are produced by filler-matrix debonding process. In addition to nonlinear behavior that has been resulted by filler-matrix debonding and was presented by Yilmizer, the formation and growing of void or cavitations has been also introduced in this model, whereas Anderson's model, most important reason for deviation of linear behavior is filler-matrix debonding and has been indicated by change of modulus. Model predictions for effects of the filler concentration and its particle size and particle size distribution for some matrix-filler systems are compared with related experimental data from literature and some investigated systems in this work. An excellent agreement even better than prediction of Anderson's model between experimental data and model predictions can be observed in most cases especially for some concentrated systems. POLYM. COMPOS., 31:1150,1155, 2010. © 2009 Society of Plastics Engineers [source]