Pseudospin 3/2 Fermions, Type-II Weyl Semimetals and Critical Weyl Semimetals in Tricolor Cubic Lattice

TL;DR

This paper introduces a cubic lattice model demonstrating high pseudospin fermions, Weyl semimetals, and critical Weyl fermions, revealing their behaviors and transitions under magnetic fields in a condensed matter system.

Contribution

It presents a simple cubic lattice model with three atoms per unit cell, showing the emergence of pseudospin-3/2 fermions, Weyl, and critical Weyl fermions at high-symmetry points and boundaries.

Findings

Realization of 4-band and 2-band touchings at high-symmetry points.

Derivation of low-energy theories for pseudospin-3/2 and Weyl fermions.

Identification of critical Weyl fermions at the boundary between type-I and type-II Weyl semimetals.

Abstract

Multi-band touchings such as 3-band, 6-band and 8-band touchings together with the emergence of high pseudospin fermions were predicted recently at high-symmetry points in three-dimensional space. In this paper, we propose a simple cubic model whose unit cell contains three atoms. There are 6 bands in the system due to the spin degrees of freedom. The 4-band and 2-band touchings are realized at high-symmetry points, where we derive low-energy theories, demonstrating the emergence of pseudospin-3/2 fermions and Weyl fermions, respectively. Away from the high-symmetry points, we find critical Weyl fermions present exactly at the boundary between the type-I and type-II Weyl fermions. This critical Weyl fermion transforms into the type-I or type-II Weyl fermion once the magnetic field is applied.