The temperature dependence of the energy gaps for sulfur-annealed copper indium disulfide has been studied by photorefiectance in the temperature range of 10-300 K. The sulfurannealed sample has been found to have larger transition energies, smaner positive temperature coefficients of energy gaps, and larger spin-orbit splitting energy than the as-grown sample. This can be explained by the reduction of d-level contributions in the upper valence band probably caused by the variation of lattice distance due to native defects.

We report the low-temperature far-infrared response of two prototypical spin-Peierls (SP) materials as a function of magnetic field in order to characterize the microscopic nature of the SP and high-field incommensurate phases. For the linear chain inorganic compound, GeCuO 3 , we observe that the B 3u shearing mode is sensitive to the high-field phase boundary in the H-T phase diagram, and we find Zeeman splitting of the zone-center spin-Peierls gap within the dimerized phase. In contrast, for the organic molecular conductor MEM-(TCNQ) 2 , neither the electron-phonon coupling modes nor the low-energy lattice modes were found to be sensitive to the high-field phase boundary. We attribute this difference to the extended vs molecular structure of the two solids as well as to the extent of spin localization.