Bad Metals from Fluctuating Density Waves

TL;DR

This paper links the optical and dc transport properties of bad metals to quantum critical density wave fluctuations, explaining the displaced Drude peak and T-linear resistivity through hydrodynamics.

Contribution

It provides a unified hydrodynamic theory connecting density wave fluctuations to the optical and transport behavior of bad metals.

Findings

Displaced Drude peak position scales with temperature as k_BT/ħ.

Optical conductivity shows a peak at finite frequency related to quantum critical fluctuations.

Hydrodynamic model explains T-linear resistivity and optical features in bad metals.

Abstract

Bad metals have a large resistivity without being strongly disordered. In many bad metals the Drude peak moves away from zero frequency as the resistivity becomes large at increasing temperatures. We catalogue the position and width of the `displaced Drude peak' in the observed optical conductivity of several families of bad metals, showing that $\omega_\text{peak} \sim \Delta \omega \sim k_BT/\hbar$. This is the same quantum critical timescale that underpins the $T$-linear dc resistivity of many of these materials. We provide a unified theoretical description of the optical and dc transport properties of bad metals in terms of the hydrodynamics of short range quantum critical fluctuations of incommensurate density wave order. Within hydrodynamics, pinned translational order is essential to obtain the nonzero frequency peak.