Magnetism and superconductivity of strongly correlated electrons on the triangular lattice

TL;DR

This study explores the phase diagram of the t-J model on a triangular lattice, revealing stable magnetic and superconducting phases under doping, with new insights into their coexistence and competition.

Contribution

It introduces an extended set of Gutzwiller projected fermionic wave-functions to analyze magnetic and superconducting orders in the t-J model on a triangular lattice.

Findings

Magnetic and superconducting phases are stable under different doping conditions.

Superconductivity persists down to n≈0.8 for hole doping.

Saturated ferromagnetism appears between n=0.2 and 0.8.

Abstract

We investigate the phase diagram of the \tj Model on a triangular lattice using a Variational Monte-Carlo approach. We use an extended set of Gutzwiller projected fermionic trial wave-functions allowing for simultaneous magnetic and superconducting order parameters. We obtain energies at zero doping for the spin-1/2 Heisenberg model in very good agreement with the best estimates. Upon electron doping (with a hopping integral $t<0$) this phase is surprisingly stable variationally up to $n\approx 1.4$, while the $d_{x^{2}-y^{2}}+i d_{xy}$ order parameter is rather weak and disappears at $n\approx 1.1$. For hole doping however the coplanar magnetic state is almost immediately destroyed and $d_{x^{2}-y^{2}}+i d_{xy}$ superconductivity survives down to $n\approx 0.8$. For lower $n$, between 0.2 and 0.8, we find saturated ferromagnetism. Moreover, there is evidence for a narrow spin density wave phase around $n\approx 0.8$. Commensurate flux phases were also considered, but these turned out {\em not} to be competitive at finite doping.