Hydrodynamic transport in strongly coupled disordered quantum field theories

TL;DR

This paper develops a formalism to compute thermoelectric transport in strongly coupled disordered quantum field theories, bridging hydrodynamic and non-perturbative regimes, with implications for understanding metal behavior under disorder.

Contribution

It introduces a new approach to analyze transport in strongly coupled disordered systems, extending existing methods and providing insights into the transition between coherent and incoherent metallic states.

Findings

Transport coefficients computed for strongly coupled theories without quasiparticles.

Disorder induces a transition from coherent to incoherent metallic behavior.

The formalism connects hydrodynamic, memory matrix, and holographic approaches.

Abstract

We compute direct current (dc) thermoelectric transport coefficients in strongly coupled quantum field theories without long lived quasiparticles, at finite temperature and charge density, and disordered on long wavelengths compared to the length scale of local thermalization. Many previous transport computations in strongly coupled systems are interpretable hydrodynamically, despite formally going beyond the hydrodynamic regime. This includes momentum relaxation times previously derived by the memory matrix formalism, and non-perturbative holographic results; in the latter case, this is subject to some important subtleties. Our formalism may extend some memory matrix computations to higher orders in the perturbative disorder strength, as well as give valuable insight into non-perturbative regimes. Strongly coupled metals with quantum critical contributions to transport generically transition between coherent and incoherent metals as disorder strength is increased at fixed temperature, analogous to mean field holographic treatments of disorder. From a condensed matter perspective, our theory generalizes the resistor network approximation, and associated variational techniques, to strongly interacting systems where momentum is long lived.