Thermodynamic and spectral properties of adiabatic Peierls chains

TL;DR

This paper provides exact numerical analysis of thermal fluctuations on thermodynamic and spectral properties of Peierls chains, revealing how temperature affects order, gap, and excitations in these models.

Contribution

It introduces a combined classical Monte Carlo and exact diagonalization approach to study large adiabatic Peierls chains and compares results to mean-field approximations.

Findings

Low-temperature peak in specific heat due to Peierls gap

Thermal fluctuations induce in-gap soliton-antisoliton excitations

Spectral functions show gap closing and order suppression with temperature

Abstract

We present exact numerical results for the effects of thermal fluctuations on the experimentally relevant thermodynamic and spectral properties of Peierls chains. To this end, a combination of classical Monte Carlo sampling and exact diagonalization is used to study adiabatic half-filled Holstein and Su-Schrieffer-Heeger models. The classical nature of the lattice displacements in combination with parallel tempering permit simulations on large system sizes and a direct calculation of spectral functions in the frequency domain. Most notably, the long-range order and the associated Peierls gap give rise to a distinct low-temperature peak in the specific heat. The closing of the gap and suppression of order by thermal fluctuations involves in-gap excitations in the form of soliton-antisoliton pairs, and is also reflected in the dynamic density and bond structure factors as well as in the optical conductivity. We compare our data to the widely used mean-field approximation, and highlight relations to symmetry-protected topological phases and disorder problems.