The type II Weyl semimetals at low temperatures: chiral anomaly, elastic deformations, zero sound

TL;DR

This paper explores the properties of type II Weyl semimetals at low temperatures, focusing on chiral anomaly effects, elastic deformation impacts, and zero sound modes, revealing new phenomena and potential experimental signatures.

Contribution

It introduces a detailed model of type II Weyl semimetals showing how elastic deformations influence their Fermi surface and conductivity, highlighting the emergence of zero sound modes and chiral anomaly without magnetic fields.

Findings

Chiral anomaly manifests as electron-hole pair creation under electric fields.

Elastic deformations alter the Fermi surface and induce zero sound modes.

Small elastic strains can significantly increase conductivity in intermediate states.

Abstract

We consider the properties of the type II Weyl semimetals at low temperatures basing on the particular tight - binding model. In the presence of electric field directed along the line connecting the Weyl points of opposite chirality the occupied states flow along this axis giving rise to the creation of electron - hole pairs. The electrons belong to a vicinity of one of the two type II Weyl points while the holes belong to the vicinity of the other. This process may be considered as the manifestation of the chiral anomaly that exists without any external magnetic field. It may be observed experimentally through the measurement of conductivity. Next, we consider the modification of the theory in the presence of elastic deformations. In the domain of the considered model, where it describes the type I Weyl semimetals the elastic deformations lead to the appearance of emergent gravity. In the domain of the type II Weyl semimetals the form of the Fermi surface is changed due to the elastic deformations, and its fluctuations represent the special modes of the zero sound. We find that there is one - to one correspondence between them and the sound waves of the elasticity theory. Next, we discuss the influence of the elastic deformations on the conductivity. The particularly interesting case is when our model describes the intermediate state between the type I and the type II Weyl semimetal. Then without the elastic deformations there are the Fermi lines instead of the Fermi points/Fermi surface, while the DC conductivity vanishes. However, even small elastic deformations may lead to the appearance of large conductivity.