Fluctuations and instabilities of a holographic metal

TL;DR

This paper investigates the quasinormal modes of a holographic model of strongly-coupled charged fermions, revealing hydrodynamic behavior, zero sound properties, thermodynamic instability, and a new low-temperature instability leading to striped phases.

Contribution

It introduces the analysis of quasinormal modes in a D2-D8' holographic model, uncovering a novel low-temperature instability towards inhomogeneous phases.

Findings

Hydrodynamic diffusion mode observed at small momentum.

Zero sound becomes massive above a critical magnetic field.

Identified a new instability leading to striped phases at low temperature.

Abstract

We analyze the quasinormal modes of the D2-D8' model of 2+1-dimensional, strongly-coupled, charged fermions in a background magnetic field and at nonzero density. The model is known to include a quantum Hall phase with integer filling fraction. As expected, we find a hydrodynamical diffusion mode at small momentum and the nonzero-temperature holographic zero sound, which becomes massive above a critical magnetic field. We confirm the previously-known thermodynamic instability. In addition, we discover an instability at low temperature, large mass, and in a charge density and magnetic field range near the quantum Hall phase to an inhomogeneous striped phase.