Semiclassical analysis of the Nonequilibrium Local Polaron

TL;DR

This paper develops a semiclassical framework to analyze a local polaron under nonequilibrium conditions, revealing effects like decoherence and the absence of multistability, with implications for related quantum impurity problems.

Contribution

It introduces a semiclassical analysis of nonequilibrium local polarons, connecting the Hartree-Fock approximation to a semiclassical limit and addressing multistability and decoherence.

Findings

Multistability does not occur in the nonequilibrium local polaron.

Decoherence prevents the formation of polaron features in spectral functions.

The formalism applies to the nonequilibrium Kondo problem.

Abstract

A resonant level strongly coupled to a local phonon under nonequilibrium conditions is investigated. The nonequilibrium Hartree-Fock approximation is shown to correspond to approximating the steady state density matrix by delta functions at field values to which the local dynamics relaxes in a semiclassical limit. If multiple solutions exist, all are shown to make nonvanishing contributions to physical quantities: multistability does not exist. Nonequilibrium effects are shown to produce decoherence, causing the standard expansions to converge and preventing the formation of a polaron feature in the spectral function. The formalism also applies to the nonequilibrium Kondo problem.