Polarized optical reflectance and electronic structure of the charge-density-wave materials eta- and gamma-Mo4O11

We report the polarized optical reflectance spectra of eta- and gamma-Mo4O1 1 as a function of temperature and magnetic field. Excitations are assigned and analyzed based upon eletronic band-structure calculations. The 300 K s pectra of eta- and gamma-Mo4O11 show charge transfer transitions (O 2p --> Mo 4d) near 4 eV, intraband (d --> d) transitions at similar to 1.5 eV, and a free carrier response at lower energy. The intraband (did) transition sh ows strong and unusual anisotropy in the b and c directions, which is direc tly attributable to the dispersion relations of the lower-lying d-block ban ds. The effect of charge density wave formation on the optical properties o f eta- and gamma-Mo4O11 is discussed and compared with related materials. T he magnetic field dependence of the optical constants is determined for eta -Mo4O11 and discussed in terms of field effects on the nesting vector and F ermi surface.