Classification of critical points in energy bands based on topology, scaling, and symmetry

Abstract

A critical point of the energy dispersion is the momentum where electron velocity vanishes. At the corresponding energy, the density of states (DOS) exhibits non-analyticity such as divergence. Critical points can be first classified as ordinary and high-order ones, and the ordinary critical points have been studied thoroughly by L\'eon van Hove. In this work, we describe and classify high-order critical points based on topology, scaling and symmetry, which are beyond L\'eon van Hove's framework. We show that high-order critical points can have power-law divergent DOS with particle-hole asymmetry, and can be realized at generic or symmetric momenta by tuning a few parameters such as twist angle, strain, pressure and/or external fields.