Polarization-resolved resonant Raman excitation of surface and bulk electronic bands and phonons in MBE-grown topological insulator thin films

Interaction of phonons with Dirac-like electronic states sets the fundamental limit of electron transport in topological insulators (TIs). Polarization-resolved and resonant Raman scattering of bulk and surface electronic excitation and vibrational modes in Bi 2 Te 3 and Bi 2− x Sb x Te 3− y Se y (BSTS) thin films was investigated. At photon energies ( E p ) of 1.57 and 2.54 eV, A 1 1g and A 2 1g (LO) modes in Bi 2 Te 3 and BSTS were resonantly excited owing to interband optical excitations of the surface Dirac state (DS) and bulk conduction band (CB), respectively. At room temperature, the resonance of the surface phonon of Raman and IR active modes E 1 u (LO) and A 1 1u (LO) was observed in Bi 2 Te 3 because of interband excitation of bulk CB, and interband transition of DS resonantly excited the A 2 1u (LO) surface phonon in BSTS. A Fano line-shape suggested interference in the presence of electron-phonon coupling of the surface states. Interaction of phonons with Dirac-like electronic states sets the fundamental limit of electron transport in topological insulators (TIs).