Superconductivity and spin correlation in organic conductors: a quantum Monte Carlo study

TL;DR

This study uses quantum Monte Carlo simulations to analyze superconductivity and spin correlations in organic conductors, revealing enhanced d-wave pairing linked to spin fluctuations and Fermi surface deformation effects.

Contribution

It provides the first systematic quantum Monte Carlo analysis of pairing symmetry and spin correlations in organic superconductors, highlighting the role of spin fluctuations.

Findings

Enhanced d-wave pairing correlations observed.

Spin structure factor correlates with pairing symmetry.

Fermi surface deformation affects pairing coherence.

Abstract

The d-wave pairing correlations along with spin correlation are calculated with quantum Monte Carlo method for the two-dimensional Hubbard model on lattice structures representing organic superconductors $\kappa$-(BEDT-TTF)$_2$X and (TMTSF)$_2$X. In both cases the pairing correlations for superconducting order parameters with nodes are found to be enhanced. The symmetry and the enhancement of the pairing is systematically correlated with the spin structure factor, suggesting a spin-fluctuation mediated pairing. We have further found that, as we deform the Fermi surface to make the system approach the half-filled square lattice, the coherence of the pairing saturates while the local pairing amplitude continues to increase.