Non-Equilibrium Scaling Analysis of the Kondo Model with Voltage Bias

TL;DR

This paper develops a scaling framework using flow equations to analyze the non-equilibrium Kondo model with voltage bias, highlighting decoherence effects and comparing spin dynamics with equilibrium results.

Contribution

It introduces a consistent flow equation approach to study non-equilibrium Kondo physics, incorporating decoherence effects and analyzing spin susceptibility.

Findings

Decoherence effects dominate at large voltage bias.

Spin susceptibility shows leading logarithmic corrections.

Comparison with equilibrium results reveals key differences.

Abstract

The quintessential description of Kondo physics in equilibrium is obtained within a scaling picture that shows the buildup of Kondo screening at low temperature. For the non-equilibrium Kondo model with a voltage bias the key new feature are decoherence effects due to the current across the impurity. In the present paper we show how one can develop a consistent framework for studying the non-equilibrium Kondo model within a scaling picture of infinitesimal unitary transformations (flow equations). Decoherence effects appear naturally in third order of the beta-function and dominate the Hamiltonian flow for sufficiently large voltage bias. We work out the spin dynamics in non-equilibrium and compare it with finite temperature equilibrium results. In particular, we report on the behavior of the static spin susceptibility including leading logarithmic corrections and compare it with the celebrated equilibrium result as a function of temperature.