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

Abstract

A key issue to understand the driving force and underlying physics in the isostructural $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\alpha}$ 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 $\ensuremath{\alpha}$ phase. The hybridization strength becomes weaker upon increasing temperature, and the $f$ electrons become almost fully localized at 300 K in the high-temperature $\ensuremath{\gamma}$ 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 $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\alpha}$ phase transition. Our results suggest that the character of the $f$ electrons plays a crucial role during the $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\alpha}$ phase transition.