Ultrafast measurements of mode-specific deformation potentials of Bi$_2$Te$_3$ and Bi$_2$Se$_3$

TL;DR

This study uses ultrafast x-ray diffraction and ARPES to measure and compare the deformation potentials of surface states in Bi$_2$Te$_3$ and Bi$_2$Se$_3$, providing insights into electron-phonon interactions in topological insulators.

Contribution

It introduces a methodology to experimentally quantify mode-specific electron-phonon coupling in topological insulators, enabling direct comparison with theoretical predictions.

Findings

Coupling in Bi$_2$Te$_3$ and Bi$_2$Se$_3$ is similar and matches density functional theory expectations.

Established a new experimental approach to measure electron-phonon coupling.

Results enhance understanding of fundamental electron-phonon processes in topological insulators.

Abstract

Quantifying electron-phonon interactions for the surface states of topological materials can provide key insights into surface-state transport, topological superconductivity, and potentially how to manipulate the surface state using a structural degree of freedom. We perform time-resolved x-ray diffraction (XRD) and angle-resolved photoemission (ARPES) measurements on Bi$_2$Te$_3$ and Bi$_2$Se$_3$, following the excitation of coherent A$_{1g}$ optical phonons. We extract and compare the deformation potentials coupling the surface electronic states to local A$_{1g}$-like displacements in these two materials using the experimentally determined atomic displacements from XRD and electron band shifts from ARPES.We find the coupling in Bi$_2$Te$_3$ and Bi$_2$Se$_3$ to be similar and in general in agreement with expectations from density functional theory. We establish a methodology that quantifies the mode-specific electron-phonon coupling experimentally, allowing detailed comparison to theory. Our results shed light on fundamental processes in topological insulators involving electron-phonon coupling.