In Situ Electronic Structure Study of Epitaxial Niobium Thin Films by Angle-Resolved Photoemission Spectroscopy**Supported by the National Key Research and Development Program of China under Grant No 2016YFA0300204, the National Natural Science Foundation of China under Grant Nos 11274332, 11574337, 11404360 and 11227902, the Natural Science Foundation of Shanghai under Grant No 14ZR1447600, the Strategic Priority Research Program (B) of

Abstract

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.