Unconventional temperature evolution of quantum oscillations in Sn-doped Bi$_{1.1}$Sb$_{0.9}$Te$_{2}$S topological insulator

TL;DR

This study reveals an unconventional temperature-dependent decrease in quantum oscillation frequency in Sn-doped Bi$_{1.1}$Sb$_{0.9}$Te$_{2}$S, linked to electron-phonon interactions affecting the bulk band gap and surface states.

Contribution

It demonstrates that surface quantum oscillations can be used to probe the temperature evolution of the bulk band gap in topological insulators, highlighting a novel temperature renormalization effect.

Findings

Quantum oscillation frequency decreases by ~10% from 2 to 40 K.

The change exceeds expected Dirac quasi-particle corrections.

Temperature-induced renormalization of the bulk band gap is observed.

Abstract

Among various topological insulators, Sn-doped Bi$_{1.1}$Sb$_{0.9}$Te$_{2}$S stands out for its exceptional properties. It has a wide energy gap and typically exhibits a well-isolated Dirac point and a Fermi level positioned within the gap. The samples we present display metallic-like low-temperature resistivity attributed to surface states, pronounced quantum oscillations observable even at 40 K, and a Fermi level located approximately 100 meV above the Dirac point. In this work, we report an unusual effect: a strong temperature dependence of the quantum oscillation frequency, which decreases by around 10\% between 2 and 40 K. This reduction significantly exceeds the expected effects of the Sommerfeld and topological corrections for Dirac quasi-particles, which could account for only one-eighth of the observed change. We attribute this change to the temperature-induced renormalization of the bulk band gap size due to electron-phonon interactions, which in turn affect the position of the surface Dirac point within the gap. Furthermore, we propose that in this compound, surface quantum oscillations can serve as a precise tool for investigating the low-temperature evolution of the bulk band gap size.