Momentum dependence of 4f hybridization in heavy-fermion compounds: Angle-resolved photoemission study of YbIr2Si2 and YbRh2Si2

Heavy-fermion compounds YbIr2Si2 and YbRh2Si2 were studied by means of angle-resolved photoemission (PE). The splittings and dispersions of the 4f(13) bulk and surface PE signals in the region of the expected energy crossings of the 4f final states and the valence bands in the Brillouin zone are observed. The experimental results are explained in terms of a simplified periodic Anderson model by a momentum dependence of the electron hopping matrix element between the 4f and valence-band states.