Abstract
The identification of a non-trivial band topology usually relies on directly probing the protected surface/edge states. But, it is difficult to achieve electronically in narrow-gap topological materials due to the small (meV) energy scales. Here, we demonstrate that band inversion, a crucial ingredient of the non-trivial band topology, can serve as an alternative, experimentally accessible indicator. We show that an inverted band can lead to a four-fold splitting of the non-zero Landau levels, contrasting the two-fold splitting (spin splitting only) in the normal band. We confirm our predictions in magneto-transport experiments on a narrow-gap strong topological insulator, zirconium pentatelluride (ZrTe5), with the observation of additional splittings in the quantum oscillations and also an anomalous peak in the extreme quantum limit. Our work establishes an effective strategy for identifying the band inversion as well as the associated topological phases for future topological materials research.
Highlights
The identification of a non-trivial band topology usually relies on directly probing the protected surface/edge states
We argue that when the contribution of the k2 term is comparable to or larger than that of the Fermi velocity (∝k), the band inversion manifests itself as a second energy extremum in the Brillouin zone, while the normal band remains a single extremum at the zone center
We show that the second energy extremum in the band inversion case leads to a four-fold splitting of the density of states (DOS) in a magnetic field as well as an anomalous peak feature beyond the quantum limit
Summary
The identification of a non-trivial band topology usually relies on directly probing the protected surface/edge states. For topological insulators (TIs), the non-trivial band topology features an inverted gap in the bulk and Dirac-like surface/edge states. The latter has been the smoking gun evidence for identifying TIs in previous studies[1,2]. Finding surface/edge states is challenging near the semiconductor to semimetal transition, where a normal insulator (NI) closes its bandgap and reopens to form an inverted gap in the TI phase[3,4] In this regime, due to the small bandgap (on the meV energy scale), the electronic response of the surface/edge states is buried in that of the bulk. Our results supplement the popular magneto-transport technique with the decisive power in determining the band topology of the emergent topological materials, and provide new perspectives in understanding their exotic behaviors
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