Study on Cross-Over Change from Metal to Insulator in the Electronic States of Copper-Spinel Compounds under High Pressure

Spinel type of compounds CuIr 2 Se 4 and CuRh 2 S 4 at atmospheric pressure are metal at all temperature regions, but undergo a stabilization of insulating phase from metal phase under high pressure. In order to study the cross-over change in the electronic states from metal to insulator of both specimens under high pressure, we performed a spectromicroscopic measurement in the far-infrared to visible region under high pressure up to 8 GPa by a diamond-anvil-cell at SPring-8. Obtained results on the cross-over change in the electronic states under pressure are explained by the change in the degree of the hybridization of the Ir-5 d (Rh-4 d ) states around the Fermi level.