Observation of a mixed pairing state in Ru microdomains embedded in $S{r}_{2}Ru{O}_4$

Abstract

We report first measurements on tunneling into the {\it interior} of a Ru microdomain embedded in bulk chiral p-wave superconductor Sr${}_2$RuO${}_4$. The junctions were prepared by pressing a pure In wire onto the $ab$ face of a Ru-containing Sr${}_2$RuO${}_4$ single crystal. Below the superconducting transition temperature ($T_c$) of Sr${}_2$RuO${}_4$ (= 1.5 K), we observed a zero-bias conductance peak (ZBCP) associated with the proximity-induced p-wave superconductivity. However, below 0.44 K, roughly the $T_c$ of bulk Ru (= 0.5 K), an unexpected Ru gap and a broad ZBCP superimposed with subgap features were found to emerge, with unusual magnetic field dependences. We argue that the new features resulted from a mixed pairing state featuring intrinsic $s$- and $p$-wave condensates in the interior of a Ru microdomain embedded in Sr${}_2$RuO${}_4$.

4 pages, 3 figures