Quantum critical theories in a periodic potential: strange metallic thermoelectric and magnetotransport

TL;DR

This paper investigates 2D quantum critical systems with strong translational symmetry breaking, revealing unique transport properties such as enhanced conductivity, bad-metal behavior, and linear magnetoresistance, modeled holographically via black holes.

Contribution

It introduces a holographic model of quantum critical theories with zero-average chemical potential lattice, uncovering distinctive transport signatures under strong symmetry breaking.

Findings

Systems become better conductors with strong lattice disorder.

Exhibit bad-metal electrical transport with Drude-like thermal behavior.

Show approximately linear magnetoresistance at large magnetic fields.

Abstract

We study DC and AC thermoelectric and magneto-transport in 2D quantum critical theories with strong translational symmetry breaking due to a % varying chemical potential lattice with zero average $\bar{\mu}=0$. The combination of quantum criticality and the absence of the average natural scale implies that such systems have idiosyncratic signatures that may apply more generally when the variance in the lattice potential far exceeds the average or for strong translational symmetry breaking in general. We model such theories holographically through near-extremal AdS black holes. We find that these systems (a) become \emph{better} conductors. In a 2D lattice, this can be explained by currents flowing around obstacles; (b) exhibit bad-metal electrical transport with Drude-like thermal transport, though it is not Drude, and, notably, (c) display an approximately $B$-linear longitudinal magnetoresistance at large fields, similar to Effective Medium Theory. We comment on how these results may apply when $\bar{\mu}\neq 0$.