Revisiting superconductivity in the extended one-band Hubbard model: pairing via spin and charge fluctuations

TL;DR

This study explores how electron density, band, and interaction parameters influence superconducting instabilities in the extended Hubbard model, revealing diverse pairing symmetries and phase transitions within a spin-fluctuation framework.

Contribution

It provides a comprehensive phase diagram analysis of pairing symmetries in the extended Hubbard model using RPA, including effects of longer-range interactions and attractive nearest-neighbor terms.

Findings

Different pairing symmetries dominate depending on interaction parameters.

Boundaries between superconducting phases can be first-order or involve time-reversal symmetry breaking.

Attractive interactions can enhance specific triplet or singlet pairing channels.

Abstract

The leading superconducting instabilities of the two-dimensional extended repulsive one-band Hubbard model within spin-fluctuation pairing theory depend sensitively on electron density, band and interaction parameters. We map out the phase diagrams within a random phase approximation (RPA) spin- and charge-fluctuation approach, and find that while $B_{1g}$ ($d_{x^2-y^2}$) and $B_{2g}$ ($d_{xy}$) pairing dominates in the absence of repulsive longer-range Coulomb interactions $V_{\rm NN}$, the latter induces pairing in other symmetry channels, including e.g $A_{2g}$ ($g$-wave), nodal $A_{1g}$ (extended $s$-wave), or nodal $E_u$ ($p$-wave) spin-triplet superconductivity. At the lowest temperatures, transition boundaries in the phase diagrams between symmetry-distinct spin-singlet orders generate complex time-reversal symmetry broken superpositions. By contrast, we find that boundaries between singlet and triplet regions are characterized by first-order transitions. Finally, motivated by recent photoemission experiments, we have determined the influence of an additional explicitly attractive nearest-neighbor interaction, $V_{\rm NN}<0$, on the superconducting gap structure. Depending on the electronic filling, such an attraction boosts $E_u$ ($p$-wave) spin-triplet or $B_{1g}$ ($d_{x^2-y^2}$) spin-singlet ordering.