Magneto-optic signatures in the gapped Dirac semimetal with mixed linear and parabolic dispersions of ZrTe₅

Abstract

In this paper, we give a systematic theoretical study on the Landau levels (LLs) and magneto-optical conductivity Re(σαα) in a gapped Dirac semimetal model with mixed linear and parabolic dispersions under a magnetic field, which was recently proposed by Jiang et al. [Phys. Rev. Lett. 125, 046403 (2020)] to explain the experimental magnetoinfrared spectroscopy in the three-dimensional ZrTe5 crystal. We find that the strong magnetic field can drive the LLs become noninverted and thus the strong topological insulator phase in ZrTe5 turns to be a trivial insulator. In the different magnetic field regions, the density of states and Re(σαα) can exhibit distinct signatures. Moreover, when the magnetic field is weak, a qualitative relation in Re(σzz) between the peaks at the saddle points is revealed as Re(σzz ζn) >Re(σzz Γ) , which is in good agreement with the experiment.

Unconventional Optical Selection Rules in ZrTe5 under an In-plane Magnetic Field

“…2, we carefully label each LL transition, and observe that, the selection rules are n → n in the longitudinal conductivity Re(σ xx ), and n → n ± 2 in the transverse conductivity Re(σ zz ). The former selection rules are the same as the previous magneto-optic studies of E B [19,[28][29][30][31]; whereas the latter ones are distinctively different from the previous studies of E ⊥ B with conventional selection rules given as n → n ± 1 [10,16,19,[26][27][28][29][30]32].…”

“…In a recent magnetoinfrared spectroscopy experiment of ZrTe 5 [12], the magnetic field was applied not only along the perpendicular z direction, but also in the x − y plane. While the magneto-optical behavior of ZrTe 5 under a perpendicular magnetic field has been studied theoretically [12,19], the LLs and magneto-optics under an in-plane magnetic field remain unexplored in quantum theory.…”