Disorder effects on triple-point fermions

TL;DR

This study explores how disorder impacts triple-point fermions in topological semimetals, revealing their robustness up to a critical disorder level and detailing how disorder affects surface states and Berry curvature.

Contribution

It provides the first detailed numerical analysis of disorder effects on triple-point fermions, including their density of states, Fermi arcs, and Berry curvature.

Findings

Triple-point fermions are robust against weak disorder.

Strong disorder leads to inter-TPF scattering destroying individual TPFs.

Disorder causes Fermi arcs to dissolve and surface Berry curvature to merge.

Abstract

The stability of three-dimensional relativistic semimetals to disorder has recently attracted great attention, but the effect of disorder remains elusive for multifold fermions, that are not present in the framework of quantum field theory. In this paper, we investigate one type of multifold fermions, so-called triple-point fermions (TPFs), which have pseudospin-1 degrees of freedom and topological charges $\pm2$. Specifically, we consider the effect of disorder on a minimal, three-band tight-binding model, which realizes the minimal number of two TPFs. The numerically-obtained, disorder-averaged density of states suggests that, within a finite energy window, the TPFs are robust up to a critical strength of disorder. In the strong disorder regime, the inter-TPF scattering is the main mechanism for destroying a single TPF. Moreover, we study the effects of disorder on the distribution of Fermi arcs and surface Berry curvature. We demonstrate that the Fermi arc retains its sharpness at weak disorder, but gradually dissolves into the metallic bulk for stronger disorder. In clean limit, the surface Berry curvature exhibits a bipolar configuration in the surface Brillouin zone. With increasing disorder, the positive and negative surface Berry curvature start to merge at the nearby momenta where the Fermi arcs penetrate into bulk.