Variational Monte Carlo studies of a t-J model on an anisotropic triangular lattice

With the insulating phase of κ-(BEDT-TTF)2X in mind, we study a t-J model on an anisotropic triangular lattice, where the hopping integral is t′ in one of the three directions, using a variational Monte Carlo method. By changing the value of t′/t, we study the stability of superconducting (SC) states with d- and d + id-wave symmetries and of an antiferromagnetic (AF) state. As t′/t decreases from 1, the stable state immediately switches from the d + id wave to the d wave. The AF state is stabilized from the normal spin liquid state for t′/t ≲ 0.7 at half filling. We also take account of Nagaoka ferromagnetism and a phase separation.