  We performed terahertz magneto-optical spectroscopy of FeSe thin film to
elucidate the charge carrier dynamics. The measured diagonal (longitudinal) and
off-diagonal (Hall) conductivity spectra are well reproduced by two-carrier
Drude model, from which the carrier densities, scattering times and effective
masses of electron and hole carriers are determined in a wide range of
temperature. The hole density decreases below the structural transition
temperature while electron density increases, which is attributed to the band
structure modification in the electronic nematic phase. The scattering time of
the hole carrier becomes substantially longer than that of the electron at
lower temperature, which accounts for the increase of the positive dc Hall
coefficient at low temperature.
