Pressure suppression of unconventional charge-density-wave state in   PrRu4P12 studied by optical conductivity
  Optical conductivity s(w) of PrRu4P12 has been studied under high pressure to 14 GPa, at low temperatures to 8 K, and at photon energies 12 meV-1.1 eV. The energy gap in s(w) at ambient pressure, caused by a metal-insulator transition due to an unconventional charge-density-wave formation at 63 K, is gradually filled in with increasing pressure to 10 GPa. At 14 GPa and below 30 K, s(w) exhibits a pronounced Drude-type component due to free carriers. This indicates that the initial insulating ground state at zero pressure has been turned into a metallic one at 14 GPa. This is consistent with a previous resistivity study under pressure, where the resistivity rapidly decreased with cooling below 30 K at 14 GPa. The evolution of electronic structure with pressure is discussed in terms of the hybridization between the 4f and conduction electrons. 
H. Okamura, N. Ohta, A. Takigawa, I. Matsutori, K. Shoji, K. Miyata,   M. Matsunami, H. Sugawara, C. Sekine, I. Shirotani, H...
cond-mat.str-el