Local Ir dedimerization followed by ligand-hole hopping in X-ray irradiated thiospinel

Hiraka, Haruhiro*; Matsumura, Daiju   ; Horigane, Kazumasa*; Mizuki, Junichiro*

The extended X-ray-absorption fine structure of a spinel CuIr(SSe) powder sample, which has the charge-ordered temperature = 190 K, was determined at the Ir edge for a wide temperature range. All the local structure parameters on the Ir-Ir bonds signified the second structural change at 70 K. Remarkably, the number of Ir dimers decreased by 10% below , which indicates partial dedimerization by X-ray irradiation. We also reanalyzed the resistance data of CuIrS with the variable-range hopping model by focusing on the density of states. The X-ray-induced decrease in resistance was quantitatively explained as a result of the increase in the density of states, which was attributed to the release of holes from the 10%-dedimerized Ir ions. We suppose that the released holes hop over the ligand chalcogen site.