Little-Parks oscillations with half-quantum fluxoid features in Sr2RuO4 micro rings

TL;DR

This study reports the first observation of Little-Parks oscillations indicating fluxoid quantization in Sr2RuO4 micro rings, revealing features consistent with half-quantum fluxoids in a spin-triplet superconductor.

Contribution

It demonstrates the detection of half-quantum fluxoid features in Sr2RuO4 micro rings using resistance measurements under magnetic fields, a novel experimental achievement.

Findings

Clear Little-Parks oscillations observed in Sr2RuO4 micro rings.

Magnetovoltage maxima convert to minima above 10 mT in in-plane fields.

Evidence of fluxoid quantization consistent with half-quantum fluxoids.

Abstract

In a micro ring of a superconductor with a spin-triplet equal-spin pairing state, a fluxoid, a combined object of magnetic flux and circulating supercurrent, can penetrate as half-integer multiples of the flux quantum. A candidate material to investigate such half-quantum fluxoids is Sr$_\mathsf{2}$RuO$_\mathsf{4}$. We fabricated Sr$_\mathsf{2}$RuO$_\mathsf{4}$ micro rings using single crystals and measured their resistance behavior under magnetic fields controlled with a three-axes vector magnet. Proper Little-Parks oscillations in the magnetovoltage as a function of an axially applied field, associated with fluxoid quantization are clearly observed, for the first time using bulk single crystalline superconductors. We then performed magnetovoltage measurements with additional in-plane magnetic fields. By carefully analyzing both the voltages $V_+$ ($V_-$) measured at positive (negative) current, we find that, above an in-plane threshold field of about 10 mT, the magnetovoltage maxima convert to minima. We interpret this behavior as the peak splitting expected for the half-quantum fluxoid states.