High-temperature transport and polaron speciation in the anharmonic Holstein model

TL;DR

This paper investigates high-temperature electron transport in the anharmonic Holstein model, revealing a polaron 'speciation' phenomenon at strong coupling and analyzing the transition to localization as phonons become quasistatic.

Contribution

It introduces the concept of polaron 'speciation' driven by energy conservation in anharmonic systems at high temperatures, providing controlled calculations for both weak and strong coupling regimes.

Findings

Identification of multiple polarons at strong coupling

Explicit calculations of dc and ac responses

Discussion of polaron breakdown and localization onset

Abstract

We study the finite-temperature transport of electrons coupled to anharmonic local phonons. Our focus is on the high-temperature incoherent regime, where controlled calculations are possible both for weak and strong electron--phonon coupling. At strong coupling, the dynamics is described in terms of a multiple-species gas of small polarons: this emergent `speciation' is driven by energy conservation. We explicitly compute the dc and ac response in this regime. We discuss the breakdown of the polaron picture, and the onset of localization, in the limit where phonons become quasistatic.