Tsutomu Watanabe — Page 2

arXiv2004

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\lsim 0.7 at half filling. We also take account of Nagaoka ferromagnetism and a phase separation.

cond-mat.supr-con↗

arXiv2004

Variational Monte Carlo Studies of Pairing Symmetry for the t-J Model on a Triangular Lattice

As a model of a novel superconductor Na_xCoO_2\cdotyH_2O, a single-band t-J model on a triangular lattice is studied, using a variational Monte Carlo method. We calculate the energies of various superconducting (SC) states, changing the doping rate δand sign of t for small J/|t|. Symmetries of s, d, and d+id (p+ip and f) waves are taken up as candidates for singlet (triplet) pairing. In addition, the possibility of Nagaoka ferromagnetism and inhomogeneous phases is considered. It is revealed that, among the SC states, the d+id wave always has the lowest energy, which result supports previous mean-field studies. There is no possibility of triplet pairing, although the f-wave state becomes stable against a normal state in a special case (δ=0.5 and t<0). For t<0, the complete ferromagnetic state is dominant in a wide range of δand J/|t|, which covers the realistic parameter region of superconductivity.

cond-mat.supr-con↗