Electronic structure of YbNiX sub(3) (X =Si, Ge) studied by hard X-ray photoemission spectroscopy

lectronic structure of the Kondo lattices YbNiX sub(3) (X =Si, Ge) has been investigated by means of hard x-ray photoemission spectroscopy (HAXPES) with h nu = 5.95 keV. From the Yb 3d HAXPES spectra, the Yb valence in YbNiSi sub(3) is estimated to be 2.92, which is almost temperature-independent. On the other hand, the valence in YbNiGe sub(3) is estimated to be 2.48 at 300 K, showing significant valence fluctuation, and gradually decreases to 2.41 at 20 K on cooling. The Ni 2p sub(3/2) and Yb super(3+) 4f peaks exhibit opposite energy shifts amounting to 0.6 eV between YbNiSi sub(3) and YbNiGe sub(3). We propose a simple model for the electronic structure of YbNiX sub(3) based on the HAXPES results. ( copyright 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)