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P Wölfle

Publications and source records attributed to P Wölfle.

At least 19 recordsLinked to original sources
PubMed2003

Nonequilibrium transport through a Kondo dot in a magnetic field: perturbation theory and poor man's scaling.

We consider electron transport through a quantum dot described by the Kondo model in the regime of large transport voltage V in the presence of a magnetic field B with max((V,B)>>T(K). The electric current I and the local magnetization M are found to be universal functions of V/T(K) and B/T(K), where T(K) is the equilibrium Kondo temperature. We present a generalization of the perturbative renormali-zation group to frequency dependent coupling functions, as necessitated by the structure of bare perturbation theory. We calculate I and M within a poor man's scaling approach and find excellent agreement with experiment.

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PubMed2002

Pseudogaps in an incoherent metal.

How are the properties of a metal changed by strong inelastic scattering? We investigate this question within the two-dimensional t-J model using extended dynamical mean field theory and a generalized noncrossing approximation. Short-ranged antiferromagnetic fluctuations lead to a strongly incoherent single particle dynamics, large entropy, and resistance. Close to the Mott transition at low hole doping a pseudogap opens, accompanied by a drop in resistivity and an increase in the Hall constant for both lower temperatures T and doping levels. The behavior obtained bears surprising similarity to properties of the cuprates.

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PubMed2001

Kondo effect in quantum dots at high voltage: universality and scaling.

We examine the properties of a dc-biased quantum dot in the Coulomb blockade regime. For voltages V that are large compared to the Kondo temperature T(K), the physics is governed by the scales V and gamma, where gamma approximately V/ln(2)(V/T(K)) is the nonequilibrium decoherence rate induced by the voltage-driven current. Based on scaling arguments, self-consistent perturbation theory, and perturbative renormalization group, we argue that due to the large gamma the system can be described by renormalized perturbation theory in 1/ln(V/T(K))<<1. However, in certain variants of the Kondo problem, two-channel Kondo physics is induced by a large voltage V.

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PubMed2001

Quasiclassical negative magnetoresistance of a 2D electron gas: interplay of strong scatterers and smooth disorder.

We study the quasiclassical magnetotransport of noninteracting fermions in two dimensions moving in a random array of strong scatterers (antidots, impurities, or defects) on the background of a smooth random potential. We demonstrate that the combination of the two types of disorder induces a novel mechanism leading to a strong negative magnetoresistance, followed by the saturation of the magnetoresistivity rho(xx)(B) at a value determined solely by the smooth disorder. Experimental relevance to the transport in semiconductor heterostructures is discussed.

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PubMed2001

Emergence of anomalous distributions in disordered systems.

The present day non-gaussian distribution of mass density of the universe evolved from an initial gaussian distribution in the presence of nonlinear interactions. We discuss an analog in disordered condensed matter system where increasing the disorder changes the distribution of conductances from a gaussian at weak disorder to a log-normal at strong disorder. The highly asymmetric "one-sided" log-normal distribution in the intermediate crossover regime can be understood as a simple hybrid of these two limiting distributions.

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PubMed2000

Acoustoelectric current and pumping in a ballistic quantum point contact.

The acoustoelectric current induced by a surface acoustic wave (SAW) in a ballistic quantum point contact is considered using a quantum approach. We find that the current is of the "pumping" type and is not related to drag, i.e., to the momentum transfer from the wave to the electron gas. At gate voltages corresponding to the plateaus of the quantized conductance the current is small. It is peaked at the conductance step voltages. The peak current oscillates and decays with increasing SAW wave number for short wavelengths. These results contradict previous calculations, based on the classical Boltzmann equation.

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