Valence transition induced changes of the electronic structure in EuPd2Si2

Abstract

We present the results of hard x-ray angle-resolved photoemission spectroscopy and photoemission diffraction measurements performed on high-quality single crystals of the valence transition compound EuPd 2 Si 2 for temperatures 25 K T 300 K. At low temperatures, we observe a Eu 4 f valence v = 2.5, which decreases to v = 2.1 for temperatures above the valence transition around T V ≈ 160 K. The experimental valence numbers resulting from an evaluation of the Eu(III)/Eu(II) 3d core levels, are used for calculating band structures using density functional theory. The valence transition significantly changes the band structure as determined by angle-resolved photoemission spectroscopy. In particular, the Eu 5d valence bands are shifted to lower binding energies with increasing Eu 4 f occupancy. To a lesser extent, bands derived from the Si 3p and Pd 4d orbitals are also affected. This observation suggests a partial charge transfer between Eu and Pd/Si sites. Comparison with ab initio theory shows a good agreement with experiment, in particular concerning the unequal band shift with increasing Eu 4 f occupancy.