Vortex lattice structures of Sr$_2$RuO$_4$

TL;DR

This paper investigates the vortex lattice structures in Sr$_2$RuO$_4$, revealing how magnetic field orientation affects lattice symmetry and providing insights into the superconducting pairing symmetry and orbital contributions.

Contribution

It demonstrates the existence of two superconducting transitions under certain conditions and predicts vortex lattice geometries based on field direction and symmetry considerations.

Findings

Two superconducting transitions when zero-field state breaks time reversal symmetry.

Square vortex lattice expected along the c-axis.

Lattice orientation reveals relevant Ru 4d orbitals.

Abstract

The vortex lattice structures of Sr$_2$RuO$_4$ for the odd parity representations of the superconducting state are examined for the magnetic field along the crystallographic directions. Particular emphasis is placed upon the two dimensional representation which is believed to be relevant to this material. It is shown that when the zero-field state breaks time reversal symmetry, there must exist two superconducting transitions when there is a finite field along a high symmetry direction in the basal plane. Also it is shown that a square vortex lattice is expected when the field is along the $c$-axis. The orientation of the square lattice with respect to the underlying ionic lattice yields information as to which Ru 4d orbitals are relevant to the superconducting state.