Localized to itinerant transition of f electrons in ordered Ce films on W(110)

A key issue to understand the driving force and underlying physics in the isostructural gamma-alpha transition in Cerium is the character of the 4f states, whether it is localized or itinerant. Here the surface topography and electronic structure of the well-ordered Ce metal films on a W(110) substrate were investigated by using scanning tunneling microscopy, angle-resolved photoemission spectroscopy and density functional theory, and single-site dynamical mean-field theory calculations. Three nearly flat f bands can be observed, and a weakly dispersive quasiparticle band near the Fermi level has been directly observed at low temperature, indicating the hybridization between f electrons and conduction electrons in the low-temperature a phase. The hybridization strength becomes weaker upon increasing temperature, and the f electrons become almost fully localized at 300 K in the high-temperature. phase. The observed localized-to-itinerant transition of the f electrons with decreasing temperature gives direct experimental proof for the changes of the 4f character in the isostructural gamma-alpha phase transition. Our results suggest that the character of the f electrons plays a crucial role during the gamma-alpha phase transition.