Valence transition in polycrystalline Eu(Rh1-xCox)2Si2 studied by hard x-ray photoemission spectroscopy

We have investigated bulk-derived electronic structure of the valence transition system Eu(Rh1-xCox)2Si2 with x = 0 and 0.4 by means of hard x-ray photoemission spectroscopy. The Eu mean valence evaluated from the Eu 3d spectrum for x = 0.4 gradually changes from 2.57 at 300 K to 2.92 at 20 K. On the other hand, the valence for x = 0 retains ∼2.1 in the temperature range from 300 to 20 K. Furthermore, the Eu2+ 4f component in the valence band for x = 0.4 was shifted by 150 meV towards the Fermi level compared to that for x = 0. Present results suggest that the increase in the hybridization strength between Eu 4f and conduction electrons induces the valence transition, which is consistent with the Kondo volume collapse model.