Chiral anomaly enhancement and photo-irradiation effects in multi-band touching fermion systems

Abstract

Multi-band touchings together with the emergence of fermions exhibiting linear dispersions have recently been predicted and realized in various materials. We first investigate the Adler-Bell-Jackiw chiral anomaly in these multi-band touching semimetals when they are described by the pseudospin operator in high dimensional representation. By evaluating the Chern number, we show that the anomalous Hall effect is enhanced depending on the magnitude of the pseudospin. It is also confirmed by the analysis of the Landau levels when magnetic field is applied. Namely, charge pumping occurs from one multi-band touching point to another through multi-channel Landau levels in the presence of parallel electric and magnetic fields. We also show a pair annihilation of two multi-band touching points by photo-irradiation. Furthermore, we propose generalizations of Dirac semimetals, multiple-Weyl semimetals and loop-nodal semimetals to those composed of fermions carrying pseudospins in high dimensional representation. Finally we investigate the 3-band touching protected by the $% C_{3}$ symmetry. We show that the 3-band touching point is broken into two Weyl points by photo-irradiation.