Even-parity spin-triplet pairing by purely repulsive interactions for orbitally degenerate correlated fermions

M Zegrodnik,J Bünemann,J Spałek

doi:10.1088/1367-2630/16/3/033001

Abstract

We demonstrate the stability of the spin-triplet paired s-wave (with an admixture of extended s-wave) state for the limit of purely repulsive interactions in a degenerate two-band Hubbard model of correlated fermions. The repulsive interactions limit represents an essential extension of our previous analysis (2013 New J. Phys. 15 073050), regarded here as I. We also show that near the half-filling the considered type of superconductivity can coexist with antiferromagnetism. The calculations have been carried out with the use of the so-called statistically consistent Gutzwiller approximation (SGA) for the case of a square lattice. We suggest that the electron correlations in conjunction with the Hund's rule exchange play the crucial role in stabilizing the real-space spin-triplet superconducting state. A sizable hybridization of the bands suppresses the homogeneous paired state.

Highlights

Spin-triplet superconductivity was suggested to occur in Sr2RuO4 [1, 2], in uranium compounds [3,4,5], and in iron pnictides [6, 7]
In the last two cases of continuous fermionic systems, which are regarded as paramagnets with an enhanced magnetic susceptibility, a singlecomponent Landau Fermi-liquid picture was taken as a starting point and the pairing of the odd parity (p-wave type) was due to the exchange of paramagnons when combined with the Pauli exclusion principle
The Hunds rule in conjunction with remaining local Coulomb interactions are either treated in the Hartree–Fock approximation [20] or a semi-phenomenological negative-U intersite attraction [21] is introduced

Summary

Introduction

Spin-triplet superconductivity was suggested to occur in Sr2RuO4 [1, 2], in uranium compounds [3,4,5], and in iron pnictides [6, 7]. One should notice some similarities between the considered pairing mechanism and the single-band real space spin-singlet pairing considered for the Hubbard [28] and t-J models [29, 30] of correlated systems In this respect, the present work contributes to the universality of the exchange-interaction induced local pairing since the concept of exchange interaction is tied in a fundamental manner to the antisymmetry of the many-fermion wave function [31]

Model and method

Aim

Results in the purely repulsive interactions limit