Reentrant Landau Levels in a Dirac topological insulator

TL;DR

This paper reports the discovery of a novel reentrant Landau level regime in the Dirac topological insulator ZrTe5, characterized by anomalous oscillations and non-standard Landau level behavior beyond the quantum limit.

Contribution

It introduces a new quantization regime in ZrTe5 where Landau levels re-cross the Fermi energy, challenging standard models and advancing understanding of topological insulator electronic structures.

Findings

Observation of non-1/B periodic oscillations in ZrTe5

Identification of Landau level re-crossing at high magnetic fields

Deviation from Lifshitz-Kosevich theory in the quantum limit

Abstract

The quantum limit, where magnetic fields confine carriers to the lowest Landau level, is predicted to host exotic quantum phases arising from strengthened electronic correlations, reduced dimensionality, and increased degeneracy. We report a novel quantization regime realized in the ultra-quantum limit of the narrow-gap Dirac insulator ZrTe5, marked by anomalous magnetoresistance oscillations. These oscillations, measured in ZrTe5 single crystals down to 700 mK and up to 60 T, are distinctly non-1/B periodic and persist for magnetic fields well beyond the quantum limit. In this regime, the competition between Zeeman and cyclotron energies drives a nonlinear evolution and back-bending of Landau levels, causing low-index levels to re-cross the Fermi energy at high fields. This mechanism departs from the standard Lifshitz-Kosevich description and provides a framework to describe how the electronic structure in topological Dirac insulators evolves beyond the quantum limit.