Fine electronic structure and 5f-electron localized–itinerant transition in uranium films

Uranium, the heaviest natural element, exhibits rich and complex physical behavior, including three types of charge density wave transitions and superconductivity at low temperatures. It is widely believed that these phenomena are closely linked to the properties of 5f electrons, which are highly susceptible to external perturbations. To elucidate the detailed electronic structure, particularly the 5f electron signatures, we fabricated high-quality single-crystal uranium films on W (110) substrates using molecular beam epitaxy and investigated their fine electronic properties and temperature-dependent evolution by angle-resolved photoemission spectroscopy (ARPES). Our experiments reveal three electron pockets around the Γ point and direct hybridization between 5f electrons and conduction electrons at regions distant from Γ. The Kondo temperature extracted from ARPES and electrical resistance measurements is approximately 131 K, indicating that the 5f electrons transition from a high-temperature localized state to a low-temperature itinerant state in the thin film system. Additionally, we observe another flat band with an energy scale of 148 meV. The detailed electronic structure and direct evidence of the localized-to-itinerant transition of 5f electrons provided in this study advance the understanding of strong electronic correlations in uranium-based materials.