Electronic Structure of UGe$_{2\pm x}$ Thin Films from Photoelectron Spectroscopy

Abstract: Uranium digermanide UGe$2$, the first ferromagnetic superconductor, represents a key composition in the U-Ge system dominated by U-5$f$ states. To examine the impact of controlled stoichiometric deviations on the electronic structure, UGe${2\pm x}$ thin films ($0 \le x \le 1$) were prepared by triode sputtering and studied on pristine surfaces by X-ray (XPS) and Ultraviolet (UPS) photoelectron spectroscopy. XPS and UPS reveal a robust metallic valence band with a dominant U-5$f$ contribution at the Fermi level and a broad incoherent feature at higher binding energies, without qualitative changes in spectral line shape across the composition range. The experimental spectrum of UGe$_2$ thin films is well reproduced by DFT+U(ED) valence-band calculations combining density functional theory with exact diagonalization of the multiconfigurational U-5$f$ shell. These results demonstrate that the overall U-Ge electronic framework of UGe$_2$ thin films remains resilient to moderate stoichiometric deviations, providing a reliable electronic baseline for future studies of interface- and heterostructure-driven phenomena in uranium-based systems.