Helical fluctuations in the Raman response of the topological insulator Bi2Se3

TL;DR

This study investigates the Raman response of Bi2Se3, revealing a Lorentzian lineshape linked to topologically protected surface states and their scattering characteristics, highlighting the resonance and temperature dependence of these surface states.

Contribution

It provides detailed analysis of the Raman response associated with topological surface states in Bi2Se3, emphasizing the resonance conditions and scattering dynamics, which were not thoroughly characterized before.

Findings

Raman response shows Lorentzian lineshape due to surface states

Resonance energy and temperature affect the Raman signal

Scattering rate is comparable to spin-polaron systems

Abstract

The topological insulator Bi2Se3 shows a Raman scattering response related to topologically protected surface states amplified by a resonant interband transition. Most significantly this signal has a characteristic Lorentzian lineshape and spin-helical symmetry due to collision dominated scattering of Dirac states at the Fermi level E_F on bulk valence states. Its resonance energy, temperature and doping dependence points to a high selectivity of this process. Its scattering rate (Gamma=40 cm-1=5 meV) is comparable to earlier observations, e.g. in spin-polaron systems. Although the observation of topological surface states in Raman scattering is limited to resonance conditions, this study represents a quite clean case which is not polluted by symmetry forbidden contributions from the bulk