Chemical Composition Dependent Raman Scattering Spectroscopy of MBE Grown Manganese ‐ Based Bismuth Telluride Topological Insulator Thin Films

ABSTRACT Chemical composition dependent vibrational modes of manganese‐based bismuth telluride (MBT) magnetic topological insulators thin films grown by molecular beam epitaxy were studied by Raman spectroscopy and compared with the vibrational modes of Bi 2 Te 3 films. Intensity of TO mode was much stronger in Bi efficient MBT film. In contrast, vibrational cross‐section of LO mode was stronger in Bi deficient MBT compound. TO mode corresponds to in‐plane vibrations of Bi‐Te atomic layers. Deficiency of Bi atoms in the MBT indicated that the vibrational degree of freedom of Bi‐Te in the septuple unit cell was less probable. Antisymmetric out‐of‐phase vibration of Te‐Te atoms resulted in LO mode in which Bi atom was stationary, therefore vibrational cross‐section of this mode for Bi deficient MBT film was stronger. A resonantly excited E g and A 1 g modes was observed at excitation energy 1.57 eV associated to deformation potential and Frohlich electron–phonon coupling, respectively.