- Budapest, Budapest, Hungary
In the last decade, many experiments [1, 2, 3, 4] were performed on thin films and narrow wires of dilute magnetic alloys (e.g. Au(Fe), Cu(Fe), Cu(Cr)). The motivation of these experiments was the searching for the Kondo compensation... more
In the last decade, many experiments [1, 2, 3, 4] were performed on thin films and narrow wires of dilute magnetic alloys (e.g. Au(Fe), Cu(Fe), Cu(Cr)). The motivation of these experiments was the searching for the Kondo compensation cloud [5] as it became easy to prepare mesoscopic samples with size comparable or even smaller than the estimated size of the Kondo coherence length [5]. They found no essential change in the Kondo temperature, however, in most of the experiments [1, 2] a suppression of the Kondo resistivity amplitude was observed for small sample sizes (see Fig. 1). Covering the thin films of magnetic alloys by another pure metal layer, a partial recovery of the Kondo signal was found (proximity effect; see Fig. 2(a)) [6, 7] which was smaller for more disordered overlayers [8]. The first natural explanation [9] that the compensation cloud cannot be fully developed if the sample size at least in one dimension is smaller than the size of the cloud, was ruled out both theoretically [10, 11] and experimentally [7]. The possibility of changes in the local density of states by Friedel oscillations due to the surface was also ruled out [11] as they are localized in a few atomic distances from the surface.
Using a statistical model for the effects of decoherence [1], we show that in linear tight-binding samples ohmic conductance (resistance proportional to length) is reached for any finite density p of decoherence sites, if the chemical... more
Using a statistical model for the effects of decoherence [1], we show that in linear tight-binding samples ohmic conductance (resistance proportional to length) is reached for any finite density p of decoherence sites, if the chemical potential μ of the contacts is within a conducting band. If μ is outside a band, or if due to disorder, no bands form, for high decoherence densities p>p* still ohmic conductance is reached, where p* is a critical decoherence density. For p<p*, the sample resistance increases exponentially with the length.
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ABSTRACT We study the effect of decoherence on the electron transport in the one-dimensional Anderson model by means of a statistical model [1, 2, 3, 4, 5]. In this model decoherence bonds are randomly distributed within the system, at... more
ABSTRACT We study the effect of decoherence on the electron transport in the one-dimensional Anderson model by means of a statistical model [1, 2, 3, 4, 5]. In this model decoherence bonds are randomly distributed within the system, at which the electron phase is randomized completely. Afterwards, the transport quantity of interest (e. g. resistance or conductance) is ensemble averaged over the decoherence configurations. Averaging the resistance of the sample, the calculation can be performed analytically. In the thermodynamic limit, we find a decoherence-driven transition from the quantum-coherent localized regime to the Ohmic regime at a critical decoherence density, which is determined by the second-order generalized Lyapunov exponent (GLE) [4].
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We present a statistical model for the effects of dephasing on the transport properties of large devices. The physical picture is different from earlier models which assume that dephasing happens continuously throughout the sample,... more
We present a statistical model for the effects of dephasing on the transport properties of large devices. The physical picture is different from earlier models which assume that dephasing happens continuously throughout the sample, whereas we model the dephasing in a statistical sense, assuming a distribution of completely phase randomizing regions between which the transport is coherent and described by the nonequilibrium Green’s function method. Thus the sample is effectively divided into smaller parts making the numerical treatment more efficient. As a first application the conductances of ordered and disordered linear tight-binding chains are calculated and compared to the results of other phenomenological models in the literature.
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Following the discovery of the Kondo effect the bulk transport and magnetic behavior of the dilute magnetic alloys have been successfully described. In the last fifteen years new directions have been developed as the study of the systems... more
Following the discovery of the Kondo effect the bulk transport and magnetic behavior of the dilute magnetic alloys have been successfully described. In the last fifteen years new directions have been developed as the study of the systems of reduced dimensions and the artificial atoms so called quantum dots. In this review the first subject is reviewed starting with the scanning tunneling microscope (STM) study of a single magnetic impurity. The next subject is the reduction of the amplitude of the Kondo effect in samples of reduced dimension which was explained by the surface magnetic anisotropy which blocks the motion of the integer spin nearby the surface. The electron dephasing and energy relaxation experiments are discussed with the possible explanation including the surface anisotropy, where the situation in cases of integer and half-integer spins is very different. Finally, the present situation of the theory of dynamical structural defects is briefly presented which may lead to two-channel Kondo behavior.
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Recently, several measurements have been performed [1] to study the electron energy distribution in a metallic short wire, with large voltage applied. The measured energy relaxation can be attributed to Kondo impurities [2,3] which... more
Recently, several measurements have been performed [1] to study the electron energy distribution in a metallic short wire, with large voltage applied. The measured energy relaxation can be attributed to Kondo impurities [2,3] which mediate inelastic electron-electron scattering. We perform a systematic study of the nonequilibrium electron energy distribution in a diffusive wire with large bias in presence of Kondo impurities in the logarithmic approach. We examine the effect of finite Korringa lifetime and voltage and Kondo temperature on conditions of the experimentally observed scaling and validity of the logarithmic approach. [1] F. Pierre et al., in Kondo Effect and Dephasing in Low-Dimensional Metallic Systems (Kluwer Academic, Dordrecht 2001), pp. 119-132, cond-mat/0012038 and references therein. [2] G. Göppert, Y.M. Galperin, B.L. Altshuler, and H. Grabert, Phys. Rev. B66, 195328 (2002) and references therein. [3] J. Kroha and A. Zawadowski, Phys. Rev. Lett. 88, 176803 (2002) and references therein.
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In studying the different Kondo problems it is generally assumed that breaking the electron-hole symmetry does not affect the perturbative infrared divergencies. It is shown here that, in contrast, breaking that symmetry may in some cases... more
In studying the different Kondo problems it is generally assumed that breaking the electron-hole symmetry does not affect the perturbative infrared divergencies. It is shown here that, in contrast, breaking that symmetry may in some cases lead to observable modifications while in other cases it does not.
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Two-level systems (TLS) interacting with conduction electrons are possibly described by the two-channel Kondo Hamiltonian. In this case the channel degeneracy is due to the real spin of the electrons. The possibility of breaking that... more
Two-level systems (TLS) interacting with conduction electrons are possibly described by the two-channel Kondo Hamiltonian. In this case the channel degeneracy is due to the real spin of the electrons. The possibility of breaking that degeneracy (conservation) has interest on his own. In fact, we show that the interaction of the conduction electrons with a spin-orbit scatterer nearby the TLS leads to the breaking of the channel degeneracy (conservation) only in the case of electron-hole symmetry breaking. The generated channel symmetry breaking TLS-electron couplings are, however, too weak to result in any observable effects.