March 25, 1999
Spin fluctuation-induced superconductivity in quasi-two dimensional organic compounds, \kappa-BEDT-TTF salts, is investigated within a fluctuation exchange (FLEX) approximation using a half-filled Hubbard model with a right-angled isosceles triangular lattice (transfer matrices -\tau, -\tau^\prime), extending a previous work above T_c. An energy gap of A_2 or (x^2-y^2)-type develops with decreasing temperature below T_c more rapidly than in the BCS model. The calculated dynamical susceptibilities enough below T_c show sharp resonance peaks like those in certain cuprates superconductors. The calculated nuclear spin-lattice relaxation rate 1/T_1 shows a T^3 behavior below T_c in accordance with experiment. Estimated values of 1/T_1 are roughly consistent with experimental results. A prediction is made for the doping concentration dependence of T_c and the antiferromagnetic and superconductive instability points are calculated in the U/\tau vs. \tau^\prime/\tau plane.
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January 30, 2004
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Spin fluctuation-induced superconductivity in two-dimensional organic compounds such as \kappa-(ET)_2-X is investigated by using a simplified dimer Hubbard model with right-angled isosceles triangular lattice (transfer matrices -\tau, -\tau^\prime). The dynamical susceptiblity and the self-energy are calculated self-consistently within the fluctuation exchange approximation and the value for T_c as obtained by solving the linearized Eliashberg-type equations is in good agreem...
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July 2, 1998
I show that for a \kappa-type organic (BEDT-TTF)_2-X molecular crystal, a superconducting state with T_c ~ 10 K and gap nodes on the Fermi surface can be caused by short-ranged antiferromagnetic spin fluctuations. Using a two-band description for the anti-bonding orbitals on a BEDT-TTF dimer of the \kappa-type salt, and an intermediate local Coulomb repulsion between two holes on one dimer, the magnetic interaction and the superconducting gap-function are determined self cons...
August 1, 1999
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July 9, 1998
We study the electronic states of the anisotropic triangular lattice Hubbard model at half filling, which is a simple effective model for the organic superconducting $\kappa$-BEDT-TTF compounds. We treat the effect of the Coulomb interaction by the fluctuation exchange (FLEX) method, and obtain the phase diagram of this model for various sets of parameters. It is shown that the d-wave superconductivity is realized in the wide region of the phase diagram, next to the antiferro...
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