Tunable non-Fermi liquid phase from coupling to two-level systems

TL;DR

This paper presents a large-N theoretical model showing how electrons coupled to two-level systems can exhibit a tunable transition from Fermi liquid to non-Fermi liquid behavior, with a marginal Fermi liquid at the crossover.

Contribution

It introduces a controlled large-N model mapping to the spin-boson model, demonstrating a tunable non-Fermi liquid phase arising from electron-TLS interactions in metallic glasses.

Findings

Transition from Fermi liquid to non-Fermi liquid at strong coupling

Existence of a marginal Fermi liquid at the crossover

Fermi-liquid behavior restored beyond critical coupling

Abstract

We study a controlled large-$N$ theory of electrons coupled to dynamical two-level systems (TLSs) via spatially-random interactions. Such a physical situation arises when electrons scatter off low-energy excitations in a metallic glass, such as a charge or stripe glass. Our theory is governed by a non-Gaussian saddle point, which maps to the celebrated spin-boson model. By tuning the coupling strength we find that the model crosses over from a Fermi liquid at weak coupling to an extended region of non-Fermi liquid behavior at strong coupling, and realizes a marginal Fermi liquid at the crossover. Beyond a critical coupling strength, the TLSs freeze and Fermi-liquid behavior is restored. Our results are valid for generic space dimensions $d>1$.