Effects of off-site Coulomb interaction in a Hubbard model on a triangular lattice Original Research Article

Half-filled-band extended Hubbard models on anisotropic triangular lattices are studied using a variational Monte Carlo method, with κκ-(BEDT-TTF)2X in mind. Mott transitions are always observed at certain U . For the isotropic case, an antiferromagnetic (AF) order with 120° spin structure becomes dominant in the insulating regime. Introduction of intersite Coulomb interaction (V ) only slightly affects the AF order, but a threefold charge order appears when View the MathML sourceV/U≳13. As for superconductivity, d2d2-, dxydxy-, and f2f2-wave pairing states, which form pairs on next-nearest-neighbor sites, are stabilized with respect to the normal state for large V.