The interaction of localized 4f states with itinerant conduction-band states leads to a series of correlation phenomena that have attracted considerable interest in the last few decades. Apart from RKKY interaction, hybridization may lead to noninteger f occupations, to heavy fermion behaviour, or to a breakdown of Fermi-liquid properties. A typical system is Ce metal where hybridization of the trivalent 4f1(5d6s)3 with 4f0(5d6s)4 and 4f2(5d6s)2 configurations is responsible for α-γ phase transition. The Gunnarsson-Schönhammer approach to the single-impurity Anderson model (SIAM) allows us to relate electron spectroscopic data to results of low-energy experiments like specific heat, conductivity, and magnetization measurements and was successfully applied to many rare-earth systems. A natural weakness of SIAM is, however, that it ignores completely the effects of translation symmetry of structurally ordered solids. Consideration of the latter leads to the periodic Anderson model (PAM), for which, however, realistic theoretical approaches are still not available.
Here we present applications of PAM to consideration of k- and spin-dependent hybridization effects in Ce metal. It was shown that k-dependent splitting of the 4f ionization peak of Ce/W(110) are correctly described in the framework of the simplified periodic Anderson model (the Coulomb repulsion between two f electrons localized on the same lattice site Uff→infinity). Our results show that the wave vector is conserved upon hybridization. In case of the magnetically ordered Ce monolayer, spin- and angle-resolved resonant photoemission spectra reveal spin-dependent changes of the Fermi-level peak intensities (which reflects the hybridization strength). That indicate a spin-dependence of 4f hybridization and, thus, of 4f occupancy and local moment. The phenomenon was also described in the framework of the periodic Anderson model by 4f electron hopping into the exchange split Fe 3d derived bands that form a spin-gap at the Fermi energy around the Γ point of the surface Brillouin zone. |