A new type of cyclotron resonance from charge-impurity scattering in the bulk-insulating Bi$_2$Se$_3$ thin films

TL;DR

This study investigates the cyclotron resonance in bulk-insulating Bi$_2$Se$_3$ thin films, revealing a new resonance type linked to charge-impurity scattering, with implications for topological insulator applications.

Contribution

It introduces a novel cyclotron resonance phenomenon caused by charge-impurity scattering in bulk-insulating Bi$_2$Se$_3$ films, confirmed through magneto-terahertz spectroscopy.

Findings

Observation of sharp cyclotron resonances under magnetic fields

Confirmation of bulk-insulating nature of the films

Identification of a new resonance related to charge-impurity scattering

Abstract

This work focuses on the low frequency Drude response of bulk-insulating topological insulator Bi$_2$Se$_3$ films. The frequency and field dependence of the mobility and carrier density are measured simultaneously via time-domain terahertz spectroscopy. These films are grown on buffer layers, capped by Se, and have been exposed in air for months. Under a magnetic field up to 7 Tesla, we observe prominent cyclotron resonances (CRs). We attribute the sharp CR to two different topological surface states (TSSs) from both surfaces of the films. The CR sharpens at high fields due to an electron-impurity scattering. By using magneto-terahertz spectroscopy, we confirm that these films are bulk-insulating, which paves the way to use intrinsic topological insulators without bulk carriers for applications including topological spintronics and quantum computing.