Probing chiral superconductivity in Sr$_{2}$RuO$_{4}$ underneath the surface by point contact measurements

TL;DR

This study investigates chiral domains in Sr$_{2}$RuO$_{4}$ using point contact measurements, revealing strong surface effects and hysteresis in magnetoresistance that support the existence of chiral domains.

Contribution

It provides experimental evidence for chiral domains in Sr$_{2}$RuO$_{4}$ through point contact resistance measurements and analysis of flux pinning and hysteresis effects.

Findings

Strong flux pinning underneath the surface of Sr$_{2}$RuO$_{4}$

Hysteresis in magnetoresistance indicates domain dynamics

Thermal cycling and alternating fields can modify flux pinning

Abstract

Sr$_{2}$RuO$_{4}$ (SRO) is the prime candidate for chiral $p$-wave superconductor with critical temperature $T_{c}(SRO)\sim$1.5 K. Chiral domains with opposite chiralities $p_{x}\pm ip_{y}$ were proposed, but yet to be confirmed. We measure the field dependence of the point contact (PC) resistance between a tungsten tip and the SRO-Ru eutectic crystal, where micrometer-sized Ru inclusions are embedded in SRO with atomic sharp interface. Ruthenium is an $s$-wave superconductor with $T_{c}(Ru)\sim$0.5 K, flux pinned near the Ru inclusions can suppress its superconductivity as reflected from the PC resistance and spectra. This flux pinning effect is originated from SRO \textit{underneath} the surface and is very strong. To fully remove it, one has to thermal cycle the sample above $T_{c}(SRO)$. This resembles the thermal demagnetization for a ferromagnet, where ferromagnetic domains are randomized above its Curie temperature. Another way is by applying alternating fields with decreasing amplitude, resembling field demagnetization for the ferromagnet. The observed hysteresis in magnetoresistance can be explained by domain dynamics, providing support for the existence of chiral domains. The origin of strong pinning \textit{underneath} the surface is also discussed.