Abstract
A half-filled-band Hubbard model on an anisotropic triangular lattice ( t in two bond directions and t ' in the other) is studied using an optimization variational Monte Carlo method, to consider a Mott transition and superconductivity arising in κ-(BEDT-TTF) 2 X. Adopting wave functions with doublon–holon binding factors, we reveal that a first-order Mott (conductor-to-nonmagnetic insulator) transition takes place at U = U c , approximately of the bandwidth, for a wide t '/ t range. This transition is not directly connected to magnetism. Robust d -wave superconductivity appears in a restricted parameter range: immediately below U c and the moderate strength of frustration (\(0.4 {\lesssim} t'/t {\lesssim} 0.7\)), where short-range antiferromagnetic correlation sufficiently develops but does not come to a long-range order. The relevance to experiments is also discussed.
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