Electron-phonon coupling and surface Debye temperature of Bi2 Te3 (111) from helium atom scattering

We have studied the topological insulator Bi2Te3(111) by means of helium atom scattering. The average electron-phonon coupling λ of Bi2Te3(111) is determined by adapting a recently developed quantum-theoretical derivation of the helium scattering probabilities to the case of degenerate semiconductors. Based on the Debye-Waller attenuation of the elastic diffraction peaks of Bi2Te3(111), measured at surface temperatures between 110 and 355K, we find λ to be in the range of 0.04-0.11. This method allows us to extract a correctly averaged λ and to address the discrepancy between previous studies. The relatively modest value of λ is not surprising even though some individual phonons may provide a larger electron-phonon interaction. Furthermore, the surface Debye temperature of Bi2Te3(111) is determined as ΘD=(81±6)K. The electronic surface corrugation was analyzed based on close-coupling calculations. By using a corrugated Morse potential a peak-to-peak corrugation of 9% of the lattice constant is obtained.