Superconducting states in frustrating t-J model: A model connecting high-$T_c$ cuprates, organic conductors and Na$_x$CoO$_2$

TL;DR

This paper investigates the t-J model on a frustrated lattice, revealing a d+id superconducting state near the triangular lattice, with implications for high-$T_c$ cuprates, organic conductors, and Na$_x$CoO$_2$.

Contribution

It introduces a mean-field variational approach to identify a time-reversal symmetry-breaking superconducting state in the frustrated t-J model.

Findings

Superconducting d+id state found near triangular lattice.

Frustration extends superconductivity region for certain doping.

Possible connection of d+id state to spin gap at half-filling.

Abstract

The two-dimensional t-J model on a frustrating lattice is studied using mean-field variational theories with Gutzwiller approximation. We find that a superconducting state with broken time-reversal symmetry (d+id state) is realized in the parameter region close to the triangular lattice. The frustration enlarges the region of superconductivity when $t<0$ for the hole-doped case, which is equivalent to $t>0$ for electron doping. We also discuss the SU(2) degeneracy at half-filling. The d+id state probably corresponds to the spin gap state at half-filling.