Bulk cyclotron resonance in the topological insulator Bi2Te3

TL;DR

This study explores the bulk cyclotron resonance in Bi2Te3 topological insulator films using terahertz magneto-optical spectroscopy, revealing a field-dependent resonance linked to bulk carriers and insights into scattering mechanisms.

Contribution

It provides the first detailed analysis of bulk cyclotron resonance in undoped Bi2Te3 films, connecting the resonance to bulk carriers and elucidating the interplay of scattering processes.

Findings

The CR mode frequency increases linearly with magnetic field.

The CR width shows non-monotonous behavior with field.

The measured effective mass aligns with literature values.

Abstract

We investigated magneto-optical response of undoped Bi2Te3 films in the terahertz frequency range (0.3 - 5.1 THz, 10 - 170 cm-1) in magnetic fields up to 10 T. The optical transmission, measured in the Faraday geometry, is dominated by a broad Lorentzian-shaped mode, whose central frequency linearly increases with applied field. In zero field, the Lorentzian is centered at zero frequency, representing hence the free-carrier Drude response. We interpret the mode as a cyclotron resonance (CR) of free carriers in Bi2Te3. Because the mode's frequency position follows a linear magnetic-field dependence and because undoped Bi2Te3 is known to possess an appreciable number of bulk carriers, we associate the mode with a bulk CR. In addition, the cyclotron mass obtained from our measurements fits well the literature data on the bulk effective mass in Bi2Te3. Interestingly, the width of the CR mode demonstrates a behavior non-monotonous in field. We propose that the CR width is defined by two competing factors: impurity scattering, which rate decreases in increasing field, and electron-phonon scattering, which rate exhibits the opposite behavior.