Ultrafast Measurements of Mode-Specific Deformation Potentials of Bi_2Te_3 and Bi_2Se_3

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_2Te_3 and Bi_2Se_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_2Te_3 and Bi_2Se_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.