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

TL;DR

This study uses variational Monte Carlo to analyze pairing symmetries in a t-J model on a triangular lattice, revealing d+id wave as the most stable superconducting state and ferromagnetism in certain parameter regimes.

Contribution

It provides the first comprehensive variational Monte Carlo analysis of pairing symmetries in the t-J model on a triangular lattice, confirming the stability of d+id pairing and exploring ferromagnetic phases.

Findings

d+id wave has the lowest energy among superconducting states

Triplet pairing is unlikely; f-wave state is stable only in specific cases

Ferromagnetism dominates in wide parameter regions for t<0

Abstract

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 \delta and 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 (\delta=0.5 and t<0). For t<0, the complete ferromagnetic state is dominant in a wide range of \delta and J/|t|, which covers the realistic parameter region of superconductivity.