Fermi-surface topology and pairing symmetry in BiS2-based layered superconductors

Abstract

In order to clarify superconducting properties of BiS2-based layered superconductors LaO1−xFxBiS2, we evaluate the superconducting transition temperature Tc and analyze the gap function in a weak-coupling limit on the basis of the two-dimensional two-orbital Hubbard model. It is found that Tc becomes maximum at x=0.6 in the present calculations. For x<0.45, we obtain the d-wave gap of which line nodes do not cross the pocket-like Fermi-surface curves with the centers at X and Y points. On the other hand, for x>0.45, the extended s-wave gap is found for a couple of large Fermi-surface curves with the centers at M and X points. The variation of the Fermi-surface topology plays a key role for the gap symmetry in BiS2-based superconductors.