Strongly Interacting Weyl Semimetals: Stability of the Semimetallic Phase and Emergence of Almost Free Fermions

TL;DR

This paper demonstrates that the stability of the Weyl semimetallic phase depends on the ultraviolet cutoff and screening length, with Coulomb interactions causing significant dispersion renormalization but preserving near-free fermion behavior.

Contribution

It provides a combined analytical and Monte Carlo analysis showing the conditions for stability and the emergence of almost free fermions in interacting Weyl semimetals.

Findings

Semimetallic phase remains stable with finite cutoff and screening.

Logarithmic divergences occur without cutoff or screening.

Coulomb interactions strongly renormalize dispersion but keep fermions nearly free.

Abstract

Using a combination of analytical arguments and state-of-the-art diagrammatic Monte Carlo simulations we show that the corrections to the dispersion in interacting Weyl semimetals are determined by the ultraviolet cutoff and the inverse screening length. If both of these are finite, then the diagrammatic series is convergent even in the low-temperature limit, which implies that the semimetallic phase remains stable. Meanwhile, the absence of a UV cutoff or screening results in logarithmic divergences at zero temperature. These results highlight the crucial impact of Coulomb interactions and screening, mediated e.g. trough the presence of parasitic bands, which are ubiquitous effects in real-world materials. Also, despite sizeable corrections from Coulomb forces, the contribution from the frequency dependent part of the self energy remains extremely small, thus giving rise to a system of effectively almost free fermions with a strongly renormalised dispersion.