Here, we report on a “bulk-sensitive” magneto-infrared transmission study of ZrTe5 thin flakes in magnetic fields up to 17T. At zero magnetic field, our samples exhibit graphene-like optical absorption, which signifies their 2D nature. In a magnetic field, we observed a series of inter-band Landau level (LL) transitions that can be described by a massive Dirac fermion model with a small mass. More interestingly, we observed a four-fold splitting of low-lying LL transitions. Thanks to the newly developed circular polarized magneto-infrared capability, we were able to separate the σ+ and σ- active transitions. These observations enable further exploration of the origin in the splitting: (i) the band asymmetry breaks the degeneracy of the dipole allowed inter-band LL transitions, and (ii) the remaining two-fold degeneracy is due to a combined effect of large g-factor and a small energy gap in this system. Our results support a 2D Dirac semimetal interpretation, consistent with recent electronic transport studies [2,3]. Finally, we compare the LL structure of Dirac fermions in ZrTe5 and in other topological materials that we systematically investigated over last few years, such as HgCdTe and InAs/GaSb [4, 5, 6].
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5. F. Teppe et al. Nature Communications 7, 12576 (2016).
6. Y. Jiang et al. Physical Review B 95, 045116 (2017).