Open Access

Olena Fedchenko, Young-Joon Song, Olena Tkač, Yaryna Lytvynenko, Sergii Chernov, Andrei Gloskovskii, Christoph Schlueter, Marius Peters, Kristin Kliemt, Cornelius Krellner, Roser Valentí, Gerd Schönhense, Hans-Joachim Elmers

• We present results of hard X-ray angle-resolved photoemission spectroscopy and photoemission diffraction measurements performed on high-quality single crystals of the valence transition compound EuPd2Si2 for temperatures 25~K ≤ T ≤ 300~K. At low temperatures we observe a Eu 4f valence v=2.5, % occupation number n=6.5, which decreases to v=2.1 for temperatures above the valence transition around TV≈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 4f 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 {\it ab-initio} theory shows a good agreement with experiment, in particular concerning the unequal band shift with increasing Eu 4f occupancy.