# Ultrahigh magnetic field spectroscopy reveals the band structure of the 3D topological insulator Bi$_2$Se$_3$

## TL;DR

This study uses ultrahigh magnetic field magneto-spectroscopy to explore the complex band structure of Bi$_2$Se$_3$, revealing nonlinear Landau level dispersion and new absorption features at high energies.

## Contribution

It provides detailed experimental insights into the band structure of Bi$_2$Se$_3$ at high energies and magnetic fields, highlighting nonlinear effects and additional band features.

## Key findings

- Landau level dispersion becomes nonlinear at energies above 0.6 eV.
- New absorption features observed at 0.99 and 1.6 eV suggest higher band gaps.
- Spin-orbit splittings of conduction and valence bands measured as 0.196 and 0.264 eV.

## Abstract

We have investigated the band structure at the $\Gamma$ point of the three-dimensional (3D) topological insulator Bi$_2$Se$_3$ using magneto-spectroscopy over a wide range of energies ($0.55-2.2$\,eV) and in ultrahigh magnetic fields up to 150\,T. At such high energies ($E>0.6$\,eV) the parabolic approximation for the massive Dirac fermions breaks down and the Landau level dispersion becomes nonlinear. At even higher energies around 0.99 and 1.6 eV, new additional strong absorptions are observed with a temperature and magnetic-field dependence which suggest that they originate from higher band gaps. Spin orbit splittings for the further lying conduction and valence bands are found to be 0.196 and 0.264 eV.