Superconducting Pairing Symmetries in Anisotropic Triangular Quantum Antiferromagnets

TL;DR

This paper investigates the superconducting pairing symmetries in an anisotropic triangular lattice Hubbard-Heisenberg model, revealing a transition from gapped to gapless states depending on anisotropy, with implications for organic superconductors.

Contribution

It introduces a renormalized mean field approach to analyze pairing symmetries in a model relevant to organic superconductors, highlighting the dependence on lattice anisotropy.

Findings

Superconducting state symmetry varies with anisotropy.

Near isotropic limit, the SC state has d+id symmetry.

At small anisotropy, the SC state is d-wave and gapless.

Abstract

Motivated by the recent discovery of a low temperature spin liquid phase in layered organic compound $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ which becomes a superconductor under pressure, we examine the phase transition of Mott insulating and superconducting (SC) states in a Hubbard-Heisenberg model on an anisotropic triangular lattice. We use a renormalized mean field theory to study the Gutzwiller projected BCS wavefucntions. The half filled electron system is a Mott insulator at large on-site repulsion $U$, and is a superconductor at a moderate $U$. The symmetry of the SC state depends on the anisotropy, and is gapful with $d_{x^2-y^2}+id_{xy}$ symmetry near the isotropic limit and is gapless with $d_{x^2-y^2}$ symmetry at small anisotropy ratio.