Probing chiral superconductivity in Sr2RuO4 underneath the surface by point contact measurements

Abstract

Sr _2 RuO _4 (SRO) is the prime candidate for a chiral p-wave superconductor with critical temperature ${T}_{{\rm{c}}}(\mathrm{SRO})\sim 1.5$ K. Chiral domains with opposite chiralities ${p}_{x}\pm {{\rm{i}}{p}}_{y}$ have been proposed, but are yet to be confirmed. We measure the field dependence of the point contact (PC) resistance between a tungsten tip and an SRO–Ru eutectic crystal, where micrometer-sized Ru inclusions are embedded in SRO with an atomically sharp interface. Ruthenium is an s-wave superconductor with ${T}_{{\rm{c}}}(\mathrm{Ru})\sim 0.5$ K; flux pinned near the Ru inclusions can suppress its superconductivity, as reflected in the PC resistance and spectra. This flux pinning effect originates from SRO underneath the surface and is very strong once flux is introduced. To fully remove flux pinning, one needs to thermally cycle the sample above T _c (SRO) or apply alternating fields with decreasing amplitude. With alternating fields, the observed hysteresis in magnetoresistance can be explained by domain dynamics, providing support for the existence of chiral domains. The origin of the strong pinning could be the chiral domains themselves.

Keywords

• p-wave superconductor
• chiral domains
• point contact measurement
• strontium ruthenate
• ferromagnetic superconductor
• Sr2RuO4