Pressure Effect on Pr-based Skutterudite Compounds

The pressure-induced metal–insulator transition in PrRu 4 P 12 has been examined by the optical study at 20 K. The reflectivity and the optical conductivity clearly showed the change from an insulator to a metal across 8 GPa. The temperature-induced gap was stabilized by pressure in the realm of insulating state below 8 GPa. The typical metallic spectra with a finite Drude component were observed in both reflectivity and optical conductivity above 8 GPa.