Thin films of a three-dimensional topological insulator in a strong magnetic field: a microscopic study

TL;DR

This study uses microscopic calculations to explore the Landau level structure of thin Bi2Se3 topological insulator films under strong magnetic fields, revealing key features like the absence of the n=0 level in ultra-thin films and its evolution with thickness and field.

Contribution

It provides a detailed microscopic analysis of Landau quantization in three-dimensional topological insulator thin films, including the effects of thickness and magnetic field on surface and bulk states.

Findings

Absence of n=0 Landau level in ultra-thin films

Signature of n=0 level in five-quintuple-layer films

Field-dependent splitting and spin-polarization of the n=0 level

Abstract

The response of thin films of Bi$_2$Se$_3$ to a strong perpendicular magnetic field is investigated by performing magnetic bandstructure calculations for a realistic multi-band tight-binding model. Several crucial features of Landau quantization in a realistic three-dimensional topological insulator are revealed. The $n=0$ Landau level is absent in ultra-thin films, in agreement with experiment. In films with a crossover thickness of five quintuple layers, there is a signature of the $n=0$ level, whose overall trend as a function of magnetic field matches the established low-energy effective-model result. Importantly, we find a field-dependent splitting and a strong spin-polarization of the $n=0$ level which can be measured experimentally at reasonable field strengths. Our calculations show mixing between the surface and bulk Landau levels which causes the character of levels to evolve with magnetic field.