Observation of a mixed pairing state in Ru microdomains embedded in $Sr_2 Ru O_4$

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 ${\it{ab}}$ 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 ${\it{s}}$- and ${\it{p}}$-wave condensates in the interior of a Ru microdomain embedded in Sr$_{2}$RuO$_{4}$.