Finite temperature crossovers in periodic disordered systems

TL;DR

This paper investigates how temperature influences the static properties of periodic disordered systems, identifying crossover length scales and comparing two theoretical approaches, FRG and GVM, with a focus on disorder screening effects.

Contribution

It introduces a novel functional form for the FRG flow of the disorder correlator and compares FRG and GVM results, revealing a third length scale related to thermal disorder screening.

Findings

Excellent agreement between FRG and GVM results.

Identification of a third length scale due to thermal screening.

Explicit computation of crossover length scales at finite temperature.

Abstract

We consider the static properties of periodic structures in weak random disorder. We apply a functional renormalization group approach (FRG) and a Gaussian variational method (GVM) to study their displacement correlations. We focus in particular on the effects of temperature and we compute explicitly the crossover length scales separating different regimes in the displacement correlation function. To do so using the FRG we introduce a functional form that approximate very accurately the flow of the disorder correlator at all scales. We compare the FRG and GVM results and find excellent agreement. We show that the FRG predicts in addition the existence of a third length scale associated with the screening of the disorder by thermal fluctuations and discuss a protocol to observe it.