Single crystals of the ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$-Ru eutectic system are known to exhibit enhanced superconductivity at 3 K in addition to the bulk superconductivity of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ at 1.5 K. The 1.5 K phase is believed to be a spin-triplet, chiral $p$-wave state with a multicomponent order parameter, giving rise to chiral domain structure. In contrast, the 3 K phase is attributable to enhanced superconductivity of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ in the strained interface region between Ru inclusion of a few to tens of micrometers in size and the surrounding ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. We investigate the dynamic behavior of a topological junction, where a superconductor is surrounded by another superconductor. Specifically, we fabricated Nb/Ru/${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ topological superconducting junctions, in which the difference in phase winding between the $s$-wave superconductivity in Ru microislands induced from Nb and the superconductivity of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ mainly governs the junction behavior. Comparative results of the asymmetry, hysteresis, and noise in junctions with different sizes, shapes, and configurations of Ru inclusions are explained by the chiral domain-wall motion in these topological junctions. Furthermore, a striking difference between the 1.5 and 3 K phases is clearly revealed: the large noise in the 1.5 K phase sharply disappears in the 3 K phase. These results confirm the multicomponent order-parameter superconductivity of the bulk ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, consistent with the chiral $p$-wave state, and the proposed nonchiral single-component superconductivity of the 3 K phase.

• Received 20 March 2017
• Revised 7 May 2017

DOI:https://doi.org/10.1103/PhysRevB.95.224509