Polarized optical reflectance and electronic band structure of α′-NaV2O5

We report polarized optical reflectance studies of alpha'-NaV2O5 between 0.5 and 6 eV as a function of temperature (T) and magnetic field (H). The electronic excitations and their polarization dependence are interpreted according to our extended Huckel tight-binding polarized band structure calculations. Strong bands near 1 eV in both chain and rung directions are attributed to V did transitions. Charge transfer excitations are estimated to begin near 3.3 eV and have significant strength at 4.4 eV and above. The reflectance ratios, Delta R(T)=R(T)/R(T=4 K), measured at H=0 and 28 T, reveal broad polarization-dependent changes through the low temperature transition, T-c. Integrated intensities of Delta R features exhibit a second-order transition at 36 K in zero field and at 33+/-1 K in high field, consistent with a spin-Peierls aspect to the phase transition. [S0163-1829(99)06347-X].