Minimal electronic models for superconducting BiS2 layers

We construct minimal electronic models for a newly discovered superconductor LaO1-xFxBiS2 (T-c = 10.6 K) possessing BiS2 layers based on a first-principles band calculation. First, we obtain a model consisting of two Bi 6p and two S 3p orbitals, which give nearly electron-hole symmetric bands. Further focusing on the bands that intersect the Fermi level, we obtain a model with two p orbitals. The two bands (per BiS2 layer) have a quasi-one-dimensional character with a double minimum dispersion, which gives good nesting of the Fermi surface. At around x similar to 0.5 the topology of the Fermi surface changes, so that the density of states at the Fermi level becomes large. Possible pairing states are discussed.