Current-induced superconducting anisotropy of Sr$\mathsf{_2}$RuO$\mathsf{_4}$

TL;DR

This study investigates the anisotropic superconducting properties of Sr₂RuO₄ under current and magnetic field, revealing distinct contributions to the upper critical field behavior linked to vortex dynamics and sample imperfections.

Contribution

It introduces a method to separate current-induced and sample imperfection effects on the anisotropy of the upper critical field in Sr₂RuO₄.

Findings

Resistive Hc2 shows additional two-fold anisotropy under in-plane current.

Current-related anisotropy diminishes at low temperatures where Hc2 is suppressed.

Sample imperfections contribute to anisotropy, especially near the first-order transition region.

Abstract

In the unconventional superconductor Sr$\mathsf{_2}$RuO$\mathsf{_4}$, unusual first-order superconducting transition has been observed in the low-temperature and high-field region, accompanied by a four-fold anisotropy of the in-plane upper critical magnetic field $H_{c2}$. The origin of such unusual $H_{c2}$ behavior should be closely linked to the debated superconducting symmetry of this oxide. Here, toward clarification of the unusual $H_{c2}$ behavior, we performed the resistivity measurements capable of switching in-plane current directions as well as precisely controlling the field directions. Our results reveal that resistive $H_{c2}$ under the in-plane current exhibits an additional two-fold anisotropy. By systematically analyzing $H_{c2}$ data taken under various current directions, we succeeded in separating the two-fold $H_{c2}$ component into the one originating from applied current and the other originating from certain imperfection in the sample. The former component, attributable to vortex flow effect, is weakened at low temperatures where $H_{c2}$ is substantially suppressed. The latter component is enhanced in the first order transition region, possibly reflecting a change in the nature of the superconducting state under high magnetic field.