A Mechanism of Spin-Triplet Superconductivity in Hubbard Model on Triangular La ttice: Application to UNi_2Al_3

TL;DR

This paper explores the emergence of spin-triplet superconductivity in a Hubbard model on a triangular lattice, highlighting the role of vertex corrections and symmetry variations, with implications for understanding superconductivity in UNi_2Al_3.

Contribution

It demonstrates that vertex terms are crucial for spin-triplet pairing and shows how symmetry changes influence superconducting states in the Hubbard model.

Findings

Spin-triplet superconductivity appears near D_6 symmetry.

Vertex corrections are essential for triplet pairing.

Results suggest a link to superconductivity in UNi_2Al_3.

Abstract

We discuss the possibility of spin-triplet superconductivity in a two-dimensional Hubbard model on a triangular lattice within the third-order perturbation theory. When we vary the symmetry in the dispersion of the bare energy band from D_2 to D_6, spin-singlet superconductivity in the D_2-symmetric system is suppressed and we obtain spin-triplet superconductivity in near the D_6-symmetric system. In this case, it is found that the vertex terms, which are not included in the interaction mediated by the spin fluctuation, are essential for realizing the spin-triplet pairing. We point out the possibility that obtained results correspond to the difference between the superconductivity of UNi_2Al_3 and that of UPd_2Al_3.