  We investigated the electronic structure and lattice dynamics of multiferroic
MnWO4 by optical spectroscopy. With variation of polarization, temperature, and
magnetic field, we obtained optical responses over a wide range of photon
energies. The electronic structure of MnWO4 near to the Fermi level was
examined, with inter-band transitions identified in optical conductivity
spectra above a band-gap of 2.5 eV. As for the lattice dynamics, we identified
all the infrared transverse optical phonon modes available according to the
group-theory analysis. Although we did not observe much change in global
electronic structure across the phase transition temperatures, an optical
absorption at around 2.2 eV showed an evident change depending upon the spin
configuration and magnetic field. The behavior of this band-edge absorption
indicates that spin-orbit coupling plays an important role in multiferroic
MnWO4.
