Role of p-f Hybridization in the Metal-Non-Metal Transition of PrRu4P12
  Electronic state evolution in the metal-non-metal transition of PrRu4P12 has been studied by X-ray and polarized neutron diffraction experiments. It has been revealed that, in the low-temperature non-metallic phase, two inequivalent crystal-field (CF) schemes of Pr3+ 4f^2 electrons with Gamma_1 and Gamma_4^(2) ground states are located at Pr1 and Pr2 sites forming the bcc unit cell surrounded by the smaller and larger cubic Ru-ion sublattices, respectively. This modulated electronic state can be explained by the p-f hybridization mechanism taking two intermediate states of 4f^1 and 4f^3. The p-f hybridization effect plays an important role for the electronic energy gain in the metal-non-metal transition originated from the Fermi surface nesting. 
Kazuaki Iwasa, Lijie Hao, Tomoo Hasegawa, Toshiaki Takagi, Kenji   Horiuchi, Yoshiaki Mori, Youichi Murakami, Keitaro Kuwaha...