Out-of-equilibrium properties and non-linear effects for interacting quantum impurity systems in their strong coupling regime

TL;DR

This paper develops an exact analytical framework for out-of-equilibrium quantum impurity systems in their strong coupling regime, focusing on integrable models and providing detailed expansions for charge transport properties.

Contribution

It introduces an out-of-equilibrium strong coupling expansion for integrable quantum impurity systems, extending equilibrium results to non-linear, time-dependent regimes.

Findings

Exact expansion for charge current as a function of voltage, temperature, and frequency.

Application to the Interacting Resonant Level model yields precise low-energy behavior.

Demonstrates the approach's ability to handle non-linear and out-of-equilibrium effects in strongly coupled systems.

Abstract

We provide an exact description of out-of-equilibrium fixed points in quantum impurity systems, that is able to treat time-dependent forcing. Building on this, we then show that analytical out-of-equilibrium results, that exactly treat interactions, can be obtained in interacting quantum impurity systems in their strong coupling regime, provided they are integrable \emph{at} equilibrium and they are "super Fermi liquids", i.e. they only allow for integer charge hopping. For such systems we build an out-of-equilibrium strong coupling expansion, akin to a Sommerfeld expansion in interacting systems. We apply our approach to the Interacting Resonant Level model, and obtain the exact expansion around the low energy fixed point of the universal scaling function for the charge current as a function of voltage, temperature, and frequency, up to order seven.