Coexisting superconducting and spiral spin orders: models of ruthenate

TL;DR

This paper investigates how a spiral spin structure influences superconducting pairing in Sr2RuO4, revealing a mixed singlet-triplet state with broken time reversal symmetry, using a mean field model.

Contribution

It introduces a model showing coexistence of superconducting and spiral spin orders, with mixed pairing states and broken time reversal symmetry in Sr2RuO4.

Findings

Mixed singlet and triplet pairing states are formed.

Both states exhibit broken time reversal symmetry.

The spiral spin structure affects the pairing symmetry and properties.

Abstract

Influence of a spiral spin structure on the superconducting (SC) pairing in the most probable active $\gamma$ band of $Sr_2RuO_4$ is studied in the mean field approximation. Such structure with "incommensurate" vector $Q=2\pi(1/3,1/3)$ has been proposed as that which removes the nesting instability in $\alfa, \betta$ bands. The model pairing interaction of adjacent centres is adopted. The mixed singlet and triplet SC order is revealed. The d-wave singlet pairing is accompanied by formation of the p-wave triplet pairs with large total momentum Q and spin projections $\pm 1$ onto axis normal to the spin rotation plane of the spiral structure. Both the superconducting and normal states have a broken time reversal symmetry which might be detected by polarised photoemission.