Spin-Triplet Pairing State of Sr2RuO4 in the c-Axis Magnetic Field

TL;DR

This study explores the behavior of spin-triplet superconductivity in Sr2RuO4 under a c-axis magnetic field, revealing multiple stable pairing states, the emergence of a non-unitary state, and the stabilization of a fractional vortex lattice.

Contribution

It introduces a four-component Ginzburg-Landau model considering weak spin-orbit coupling to analyze the phase diagram and vortex structures in Sr2RuO4 under magnetic fields.

Findings

Three stable spin-triplet pairing states identified

A non-unitary state appears near the transition temperature

Fractional vortex lattice stabilized in the chiral II phase

Abstract

We investigate the spin-triplet superconducting state of Sr2RuO4 in the magnetic field along the c-axis on the basis of the four-component Ginzburg-Landau (GL) model with a weak spin-orbit coupling. We consider superconducting states described by the d-vector parallel to the ab-plane, and find that three spin-triplet pairing states are stabilized in the magnetic field-temperature phase diagram. Although a helical state is stable at low magnetic fields, a chiral II state is stabilized at high magnetic fields. A non-unitary spin-triplet pairing state appears near the transition temperature owing to the coupling of magnetic field and chirality. We elucidate synergistic and/or competing roles of the magnetic field, chirality, and spin-orbit coupling. It is shown that a fractional vortex lattice is stabilized in the chiral II phase owing to the spin-orbit coupling.