Pseudospin-3/2 fermions, type-II Weyl semimetals, and critical Weyl semimetals in tricolor cubic lattices

摘要

Multiband touchings, such as three-band, six-band, and eight-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 six bands in the system due to the spin degrees of freedom. The four-band and two-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.