# Landau level spectroscopy of massive Dirac fermions in single-crystalline ZrTe5 thin flakes

## TL;DR

This study uses infrared magneto-spectroscopy to investigate the Landau level structure of thin ZrTe5 flakes, revealing a 2D Dirac-like electronic system with a small energy gap and electron-hole asymmetry.

## Contribution

It provides a detailed model of Landau level transitions in ZrTe5, extracting key electronic parameters using the Bernevig-Hughes-Zhang Hamiltonian.

## Key findings

- Identification of a small relativistic mass gap of 9.4 meV.
- Observation of Landau level splitting due to electron-hole asymmetry.
- Quantitative determination of Fermi velocity, g-factors, and Dirac mass.

## Abstract

We report infrared magneto-spectroscopy studies on thin crystals of an emerging Dirac material ZrTe5 near the intrinsic limit. The observed structure of the Landau level transitions and zero-field infrared absorption indicate a two-dimensional Dirac-like electronic structure, similar to that in graphene but with a small relativistic mass corresponding to a 9.4 meV energy gap. Measurements with circularly polarized light reveal a significant electron-hole asymmetry, which leads to splitting of the Landau level transitions at high magnetic fields. Our model, based on the Bernevig-Hughes-Zhang effective Hamiltonian, quantitatively explains all observed transitions, determining the values of the Fermi velocity, Dirac mass (or gap), electron-hole asymmetry, and electron and hole g-factors.