Determination of the Terahertz Dielectric Function of the Topological Insulator Bi2Se3

We investigate the THz conductivity of the topological insulator Bi
2
Se
3
, in a systematic study involving samples of different thicknesses. In our analysis we compare the fits of experimental data to two suggested models, describing the electron and phonon contributions: Drude with Fano-modified Lorentzian resonance, and Drude with a two-Lorentzian resonance. Analysis of the fit accuracy suggests that the asymmetric shape of the lattice resonance in Bi
2
Se
3
might arise from the presence of a surface vibrational state, rather than from the electron-phonon Fano interference, as was previously suggested.