Two-Band Fluctuation Exchange Study on Superconductivity of β'-(BEDT-TTF)_2ICl_2 under High Pressure (Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties)

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We study the pressure dependence of the superconducting transition temperature of an organic superconductor β'-(BEDT-TTF)_2ICl_2 by applying the fluctuation exchange method to the Hubbard model on the original two-band lattice at 3/4 filling rather than the single-band model in the strong dimerization limit. Our study is motivated by the fact that hopping parameters evaluated from a firstprinciples study suggest that the dimerization of the BEDT-TTF molecules is not very strong particularly high pressures. Solving the linearized Eliashberg's equation, a d_<xy>-wavelike superconducting state with realistic values of T_c is obtained in a pressure regime somewhat higher than the actual experimental result. These results are similar to those obtained within the single-band model in the previous study by Kino et al. We conclude that the resemblance to the dimer limit is due to a combination of a good Fermi surface nesting, a large density of states near the Fermi level, and a moderate dimerization, which cooperatively enhance electron correlation effects and also the superconducting T_c.
2006-03-15