Magnetic field induced rotation of the d-vector in the spin triplet superconductor Sr$_2$RuO$_4$

TL;DR

This paper investigates how a magnetic field along the c-axis can induce a reorientation of the d-vector in the spin triplet superconductor Sr$_2$RuO$_4$, aligning theoretical predictions with experimental observations.

Contribution

It introduces a phenomenological, orbital-specific model to explain the magnetic field-induced d-vector reorientation in Sr$_2$RuO$_4$, matching experimental findings.

Findings

A c-axis magnetic field of 20 mT can reorient the d-vector from along c to the a-b plane.

The model aligns with recent experimental results on d-vector orientation.

A phase transition occurs in the d-vector orientation under applied magnetic field.

Abstract

In zero magnetic field the superconductor Sr$_2$RuO$_4$ is believed to have a chiral spin triplet pairing state in which the gap function d-vector is aligned along the crystal c-axis. Using a phenomenological but orbital specific description of the spin dependent electron-electron attraction and a realistic quantitative account of the electronic structure in the normal state we analyze the orientation of the spin triplet Cooper pair d-vector in response to an external c-axis magnetic field. We show that for suitable values of the model parameters a c-axis field of only 20 mT is able to cause a reorientation phase transition of the d-vector from along $c$ to the $a-b$ plane, in agreement with recent experiments.