Phase diagram of the two-dimensional extended Hubbard model: Phase transitions between different pairing symmetries when charge and spin fluctuations coexist

TL;DR

This study maps the phase diagram of the 2D extended Hubbard model, revealing how charge and spin fluctuations influence transitions between different superconducting pairing symmetries.

Contribution

It provides the first detailed phase diagram showing pairing symmetry transitions driven by charge and spin fluctuations in the extended Hubbard model.

Findings

Transition between dxy and dx2-y2 pairing symmetries.

Existence of f-wave pairing between dx2-y2 and CDW phases.

Pairing symmetry changes from d to f to s with increasing charge fluctuations.

Abstract

In order to explore how superconductivity arises when charge fluctuations and spin fluctuations coexist, we have obtained a phase diagram against the off-site repulsion V and band filling n for the extended, repulsive Hubbard model on the square lattice with the fluctuation exchange approximation. We have found the existence of (i) a transition between dxy and dx2-y2 pairing symmetries, (ii) f-pairing in between the dx2-y2 and CDW phases for intermediate 0.5<n<1.0 and large V, and (iii) for anisotropic cases the pairing symmetry changing, in agreement with a previously proposed ``generic phase diagram", as d -> f -> s when V (hence the charge fluctuations) are increased. All these are consequences of the structure in the charge and spin susceptibilities, which have peaks habitating at the common or segregated positions in k space.