  We study the magneto-optical (MO) response of polar semiconductor BiTeI with
giant bulk Rashba spin splitting at various carrier densities. Despite being
non-magnetic, the material is found to yield a huge MO activity in the infrared
region under moderate magnetic fields (<3 T). By comparison with
first-principles calculations, we show that such an enhanced MO response is
mainly due to the intraband transitions between the Rashba-split bulk
conduction bands in BiTeI, which give rise to distinct novel features and
systematic doping dependence of the MO spectra. We further predict an even more
pronounced enhancement in the low-energy MO response and dc Hall effect near
the crossing (Dirac) point of the conduction bands.
