Superconductivity and a Mott Transition in a Hubbard Model on an Anisotropic Triangular Lattice

TL;DR

This study uses variational Monte Carlo to analyze a Hubbard model on an anisotropic triangular lattice, revealing a first-order Mott transition and the emergence of d-wave superconductivity in specific parameter regimes, relevant to organic conductors.

Contribution

It demonstrates the occurrence of a first-order Mott transition and robust d-wave superconductivity in an anisotropic triangular lattice Hubbard model, using an optimized variational Monte Carlo approach.

Findings

First-order Mott transition at U ≈ band width for various t'/t.

Superconductivity appears below U_c with moderate frustration.

Superconductivity is associated with short-range antiferromagnetic correlations.

Abstract

A half-filled-band Hubbard model on an anisotropic triangular lattice (t in two bond directions and t' in the other) is studied using an optimization variational Monte Carlo method, to consider the Mott transition and superconductivity arising in \kappa-BEDT-TTF_2X. Adopting wave functions with doublon-holon binding factors, we reveal that a first-order Mott (conductor-to-nonmagnetic insulator) transition takes place at U=U_c approximately of the band width, for a wide range of t'/t. This transition is not directly connected to magnetism. Robust d-wave superconductivity appears in a restricted parameter range: immediately below U_c and moderate strength of frustration (0.4\lsim t'/t\lsim 0.7), where short-range antiferromagnetic correlation sufficiently develops but does not come to a long-range order. The relevance to experiments is also discussed.