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

Abstract

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 Bi₂Te₃ and Bi_2−xSb_xTe_3−ySe_y (BSTS) thin films was investigated. At photon energies (E_p) of 1.57 and 2.54 eV, A¹_1g and A²_1g (LO) modes in Bi₂Te₃ 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 E¹_u (LO) and A¹_1u (LO) was observed in Bi₂Te₃ because of interband excitation of bulk CB, and interband transition of DS resonantly excited the A²_1u (LO) surface phonon in BSTS. A Fano line-shape suggested interference in the presence of electron–phonon coupling of the surface states.