Origin of the Drude peak and of zero sound in probe brane holography

TL;DR

This paper explains the origins of the Drude peak and zero sound in probe brane holography at finite temperature, revealing how weak current non-conservation leads to these phenomena and resolving key puzzles in strange metal models.

Contribution

It analytically demonstrates the connection between weak current non-conservation and the emergence of zero sound and Drude peak in holographic probe brane models.

Findings

Zero sound mode appears at finite temperature.

Drude peak in conductivity is explained by current non-conservation.

The nonlinear current dynamics differ qualitatively from linear response.

Abstract

At zero temperature, the charge current operator appears to be conserved, within linear response, in certain holographic probe brane models of strange metals. At small but finite temperature, we analytically show that the weak non-conservation of this current leads to both a collective "zero sound" mode and a Drude peak in the electrical conductivity. This simultaneously resolves two outstanding puzzles about probe brane theories. The nonlinear dynamics of the current operator itself appears qualitatively different.