The c-f hybridization effect in the subsurface region of YbInCu4

We studied the electronic structure of YbInCu4, which exhibits a first-order valence transition, using angle-resolved photoemission spectroscopy. The dispersive conduction bands and the spin-orbit split Yb 4f7/2 and 4f5/2 states were observed clearly near the Fermi level. We revealed that a flat band located −80 meV below the 4f7/2 state shows a momentum-dependent behavior around the M¯ point of the surface Brillouin zone, and it was described by a hybridization-band picture based on the periodic Anderson model. We attributed the observed momentum-dependent behavior to the effect of hybridization between the conduction and 4f electrons in the subsurface region of YbInCu4.