Electronic structure and anomalous band-edge absorption feature in multiferroic MnWO₄: An optical spectroscopic study

We investigated the electronic structure and lattice dynamics of multiferroic MnWO₄ by optical spectroscopy. With variation in polarization, temperature, and magnetic field, we obtained optical responses over a wide range of photon energies. The electronic structure of MnWO ₄ near to the Fermi level was examined with interband 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.