Pressure and temperature dependence of the Ce valence and c-f hybridization gap in CeTIn5 (T=Co,Rh,Ir) heavy-fermion superconductors

Pressure- and temperature-induced changes in the Ce valence and c-f hybridization of the Ce115 superconductors have been studied systematically. Resonant x-ray-emission spectroscopy indicated that the increase of the Ce valence with pressure was significant for CeCoIn5, and moderate for CeIr(In0.925Cd0.075)5. We found no abrupt change of the Ce valence in the Kondo regime for CeIr(In0.925Cd0.075)5, which suggests that valence fluctuations are unlikely to mediate the superconductivity in this material. X-ray-diffraction results were consistent with the pressure-induced change in the Ce valence. High-resolution photoelectron spectroscopy revealed a temperature-dependent reduction of the spectral intensity at the Fermi level, indicating enhanced c-f hybridization on cooling.