Comparison of the phase diagram of the half-filled layered organic superconductors with the phase diagram of the RVB theory of the Hubbard-Heisenberg model

TL;DR

This paper develops an RVB theory for the Hubbard--Heisenberg model on an anisotropic triangular lattice, explaining the phase diagram of half-filled layered organic superconductors and identifying key factors influencing phase transitions.

Contribution

It introduces a theoretical framework that aligns with experimental phase diagrams and highlights the role of anisotropy and Coulomb interactions in organic superconductors.

Findings

First order transition from Mott insulator to d-wave superconductor

Superfluid stiffness is small in the superconducting phase

The ratio t'/t significantly influences the phase diagram

Abstract

We present an resonating valence bond (RVB) theory of superconductivity for the Hubbard--Heisenberg model on an anisotropic triangular lattice. We show that these calculations are consistent with the observed phase diagram of the half-filled layered organic superconductors, such as the beta, beta', kappa and lambda phases of (BEDT-TTF)_2X [bis(ethylenedithio)tetrathiafulvalene] and (BETS)_2X [bis(ethylenedithio)tetraselenafulvalene]. We find a first order transition from a Mott insulator to a d_{x^2-y^2} superconductor with a small superfluid stiffness and a pseudogap with d_{x^2-y^2} symmetry. The Mott--Hubbard transition can be driven either by increasing the on-site Coulomb repulsion, U, or by changing the anisotropy of the two hopping integrals, t'/t. Our results suggest that the ratio t'/t plays an important role in determining the phase diagram of the organic superconductors.