Origin of superconductivity in β′-(BEDT-TTF)2ICl2 under high pressure and in β-(BEDT-TTF)2X at atmospheric pressure -: art. no. 180503

We present a theoretical study on the superconductivity in beta'-(BEDT-TTF)(2)ICl2 at T-c=14.2 K under high hydrostatic pressure, which was recently found by Taniguchi and is the highest recorded for organic superconductors. Its electronic structure is well expressed by the anisotropic triangular lattice Hubbard model at half filling. In the present paper, we study this effective model by using the fluctuation-exchange approximation. In the obtained phase diagram, the superconductivity with d(x2-y2) like symmetry is realized next to the antiferromagnetic insulating phase, as a result of the one-dimensional-two-dimensional crossover driven by the pressure. The obtained maximum T-c is 16-18 K. In addition, the superconductivity in beta-(BEDT-TTF)(2)X is also understood in the same framework.