Interaction-mitigated Landau damping

TL;DR

This paper shows that interactions can suppress Landau damping in metals, allowing collective modes like plasmons to retain spectral weight by avoiding decay into particle-hole continua, with potential observations in graphene-like systems.

Contribution

It introduces a mechanism where interactions cause level repulsion, mitigating Landau damping in strongly correlated Fermi liquids, demonstrated through simplified models and large-N analysis.

Findings

Interactions can significantly reduce Landau damping effects.

Level repulsion leads to a protected spectral weight of collective modes.

Potential for observing avoided decay in graphene-like systems.

Abstract

Bosonic collective modes are ubiquitous in metals, but over a wide range of energy and momenta suffer from Landau damping, decaying into the continuum of particle-hole excitations. Here we point out that interactions can suppress this decay, protecting a finite fraction of the total spectral weight associated with the collective mode, e.g. a plasmon. The underlying mechanism is level repulsion between a discrete mode and the continuum. We demonstrate the effect using a number of simplified models of strongly correlated Fermi-liquid metals, including a ``solvable" random flavor model in the large$-N$ limit. We discuss in detail the possibility of observing such an avoided decay for plasmons in (moir\'e) graphene-like systems.