Non-Fermi-liquid behaviour of electrons coupled to gauge phonons

TL;DR

This paper demonstrates that overdamped gauge phonons, which couple to electronic currents, can induce non-Fermi-liquid behaviour in Dirac materials, with potential implications for understanding anomalous metallic states like in twisted bilayer graphene.

Contribution

It introduces a new microscopic mechanism involving gauge phonons coupling to currents, leading to non-Fermi-liquid behaviour without proximity to quantum criticality.

Findings

Overdamped gauge phonons cause deviations from Fermi-liquid theory.

Fermi-liquid behaviour persists only in a narrow energy window for positive orbital susceptibility.

Negative susceptibility leads to marginal-Fermi-liquid and then non-Fermi-liquid regimes.

Abstract

We identify overdamped gauge phonons as a new microscopic route to non-Fermi-liquid behaviour in Dirac materials. These phonons couple to electronic currents rather than densities, thereby realising a lattice analogue of transverse gauge-field mechanisms without requiring proximity to a quantum critical point. By computing the electronic self-energy with a phonon propagator dressed by electron-phonon interactions, we show that the low-energy behaviour is controlled by the orbital susceptibility chi and a dimensionless damping parameter alpha. In the overdamped regime, alpha >> 1, quasiparticles display strong deviations from Fermi-liquid theory. For chi > 0, Fermi-liquid behaviour persists only in a parametrically narrow infrared window before crossing over to non-Fermi-liquid scaling. For chi < 0, the Fermi-liquid regime is replaced by marginal-Fermi-liquid behaviour at the lowest energies, followed by a crossover to non-Fermi-liquid scaling. These results establish strain- induced gauge phonons as a promising source of anomalous metallic behaviour in systems such as twisted bilayer graphene.