Nonperturbative approach to quench dynamics. II. Universal electric current of the nonequilibrium Kondo model

TL;DR

This paper develops a nonperturbative method to analyze the steady-state electric current in the nonequilibrium Kondo model, revealing universal behaviors in both weak and strong coupling regimes, including a new ferromagnetic regime.

Contribution

It introduces a nonperturbative approach to evaluate the steady-state current in the nonequilibrium Kondo model, uncovering universal regimes and new ferromagnetic behavior.

Findings

Standard weak antiferromagnetic results confirmed

Discovery of a universal strong ferromagnetic regime

Differential conductance approaches unitarity limit at high voltage or temperature

Abstract

In the previous paper, we found a series expression for the average electric current following a quench in the nonequilibrium Kondo model driven by a bias voltage. Here, we evaluate the steady state current in the regimes of strong and weak coupling. We obtain the standard leading order results in the usual weak antiferromagnetic regime, and we also find a new universal regime of strong ferromagnetic coupling with Kondo temperature $T_K = D e^{\frac{3\pi^2}{8} \rho J}$. In this regime, the differential conductance $dI/dV$ reaches the unitarity limit $2e^2/h$ asymptotically at large voltage or temperature.