Electronic structure of single-crystalline NdO0.5F0.5BiS2 studied by angle-resolved photoemission spectroscopy

NdO0.5F0.5BiS2 is a new layered superconductor. We have studied the low-lying electronic structure of the single-crystalline NdO0.5F0.5BiS2 superconductor, whose superconducting transition temperature is 4.83 K, with angle-resolved photoemission spectroscopy. The Fermi surface consists of two small electron pockets around the X point and shows little warping along the k(z) direction. Our results demonstrate the multiband and two-dimensional nature of the electronic structure. The comparison between the photoemission data and the band calculations gives the renormalization factor of similar to 1.14, indicating the rather weak electron correlations in this material. Moreover, we found that the actual electron doping level and Fermi surface size are much smaller than what are expected from the nominal composition, which could be largely explained by the bismuth deficiency. The small Fermi pocket size and the weak electron correlations found here put strong constraints on theory, and suggest that the BiS2-based superconductors could be conventional BCS superconductors mediated by the electron-phonon coupling.