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)2X. 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 Uc and the moderate strength of frustration (0.4 ≲ t′/t ≲ 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.
- Anisotropic triangular lattice
- Antiferromagnetic correlation
- D wave
- Hubbard model
- Mott transition
- Variational Monte Carlo method