Effect of disorder on density of states and conductivity in higher order van Hove singularities in two dimensional bands

TL;DR

This paper investigates how disorder affects the density of states and conductivity in two-dimensional systems with higher order Van Hove singularities, revealing that certain features persist despite impurity smearing.

Contribution

It introduces a detailed analysis of disorder effects on HOVHS in 2D systems using diagrammatic and self-consistent Born approximations, highlighting the persistence of power-law DOS features.

Findings

DOS divergence is smeared but retains shape away from singularity

Universal ratio of DOS prefactors remains stable near HOVHS

Impurities influence conductivity regimes linked to power-law DOS

Abstract

We study systems with energy bands in two dimensions, hosting higher order Van Hove singularities (HOVHS) in the presence of disorder, using standard diagrammatic techniques for impurity averaging. In the clean limit, such singularities cause power-law divergence in the density of states (DOS), and this is expected to strongly affect electronic correlation. In order to analyse the signatures of these singularities in disordered systems, we employ various Born approximations, culminating in the self-consistent (non) Born approximation. Although the divergence of the DOS is smeared, we find that the shape of the DOS, as characterized by the power law tail and the universal ratio of prefactors, is retained slightly away from the singularity. This could help us to understand current and future experiments on materials that can be tuned to host HOVHS. The impurity induced smearing is calculated and analysed for several test cases of singularities. We also study the effects of impurities on electrical conductivity and determine the regimes where the quantitative features of the power law DOS manifest in the conductivity.