Electronic structure ofγ- andα-Ce

The $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\alpha}$ phase transition in cerium metal has been studied by temperature-dependent bremsstrahlung isochromat, core-level x-ray photoemission, and electron-energy-loss spectroscopy. The experimental results can be coherently analyzed within the many-body formalism of Gunnarsson and Sch\"onhammer. We find that the $f$ occupation ${n}_{f}$ is reduced by \ensuremath{\sim}15% while the $f$ conduction-electron hybridization $\ensuremath{\Delta}$ increases from $\ensuremath{\Delta}=25$ meV to $\ensuremath{\Delta}=60$ meV upon the $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\alpha}$ phase transition. Thus the change in the coupling $\ensuremath{\Delta}$ is concluded to be the driving mechanism for the $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\alpha}$ phase transition in Ce metal.