f Electron Hybridized States and Optical Conductivity in Ce and Yb Compounds at High Pressures

Abstract

A review is given on our recent optical conductivity [σ(ω)] studies for heavy fermion Ce and Yb compounds under high pressure. Diamond anvil cells were used to generate high pressures and synchrotron radiation at SPring-8 was used as a bright infrared source. In the measured σ(ω) spectra, a marked peak is observed in the mid-infrared range due to a high density of 4f-derived states near the Fermi level. The infrared peak exhibits significant shifts toward high and low energies in Ce and Yb systems, respectively. These opposite tendencies in Ce and Yb systems are discussed in terms of pressure-induced shifts of the 4f level, and in terms of the electron-hole symmetry.