The spin-triplet superconductivity induced by the charge fluctuation in extended Hubbard model

TL;DR

This paper investigates how charge fluctuations influence pairing symmetry in superconductivity within an extended Hubbard model, revealing conditions for triplet pairing and potential relevance to Sr2RuO4.

Contribution

It demonstrates that charge fluctuations can induce triplet superconductivity with specific symmetry, especially near van Hove singularities, expanding understanding of pairing mechanisms.

Findings

Triplet superconductivity appears below charge density wave phase for large U.

Chiral pairing state breaks time reversal symmetry, relevant to Sr2RuO4.

Fermi surface deformation enhances triplet pairing near van Hove singularities.

Abstract

The pairing symmetry in the electron mechanism for superconductivity is explored when charge fluctuations coexist with spin fluctuations. The extended Hubbard model is adopted to obtain, with the fluctuation exchange approximation, a phase diagram against the on-site Coulomb repulsion U and the off-site repulsion V for the square lattice with second-neighbor hopping t'. We have found that (i) for large U(>9) a triplet superconductivity with a sin(kx+ky) symmetry can appear just below the charge density wave phase. The pairing is degenerate with sin(kx-ky), so a chiral sin(kx+ky)+isin(kx-ky) that breaks the time reversal symmetry should result, which is a candidate for the gap function on the gamma band of Sr2RuO4 and is consistent with a recent measurement of the specific heat. (ii) By systematically deforming the Fermi surface with varied t', we have identified the region where the triplet pairing is most favored to be the region where the Fermi surface traverses the van Hove singularity with the charge susceptibility strongly enhanced.