In Situ Electronic Structure Study of Epitaxial Niobium Thin Films by Angle-Resolved Photoemission Spectroscopy

High-quality single crystalline niobium films are grown on a-plane sapphire in molecular beam epitaxy. The film is single crystalline with a (110) orientation, and both the rocking curve and the reflection high-energy electron diffraction pattern demonstrate its high-quality with an atomically smooth surface. By in situ study of its electronic structure, a rather weak electron-electron correlation effect is demonstrated experimentally in this 4d transition metal. Moreover, a kink structure is observed in the electronic structure, which may result from electron-phonon interaction and it might contribute to the superconductivity. Our results help to understand the properties of niobium deeply.