Transverse Collective Modes in Interacting Holographic Plasmas

TL;DR

This paper investigates the transverse collective modes in holographic plasmas with electromagnetic interactions, revealing mode interactions, a crossover from propagation to diffusion, and anomalous attenuation, relevant for strongly correlated quantum materials.

Contribution

It introduces a holographic model with dynamical gauge fields and explores Coulomb interaction effects on transverse modes, including mode repulsion and damping phenomena.

Findings

Mode repulsion between shear and photon modes at finite momentum relaxation

Propagation-to-diffusion crossover induced by electromagnetic interactions

Damped photon mode at zero momentum in strongly charged regimes

Abstract

We study in detail the transverse collective modes of simple holographic models in presence of electromagnetic Coulomb interactions. We render the Maxwell gauge field dynamical via mixed boundary conditions, corresponding to a double trace deformation in the boundary field theory. We consider three different situations: (i) a holographic plasma with conserved momentum, (ii) a holographic (dirty) plasma with finite momentum relaxation and (iii) a holographic viscoelastic plasma with propagating transverse phonons. We observe two interesting new features induced by the Coulomb interactions: a mode repulsion between the shear mode and the photon mode at finite momentum relaxation, and a propagation-to-diffusion crossover of the transverse collective modes induced by the finite electromagnetic interactions. Finally, at large charge density, our results are in agreement with the transverse collective mode spectrum of a charged Fermi liquid for strong interaction between quasi-particles, but with an important difference: the gapped photon mode is damped even at zero momentum. This property, usually referred to as anomalous attenuation, is produced by the interaction with a quantum critical continuum of states and might be experimentally observable in strongly correlated materials close to quantum criticality, e.g. in strange metals.