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

TL;DR

This study reveals a mixed s- and p-wave pairing state inside Ru microdomains embedded in Sr$_{2}$RuO$_{4}$, evidenced by tunneling measurements showing a Ru gap and unusual magnetic field responses below 0.44 K.

Contribution

First direct tunneling measurements inside Ru microdomains in Sr$_{2}$RuO$_{4}$ showing evidence of a mixed pairing state with s- and p-wave components.

Findings

Observation of a Ru gap below 0.44 K.

Emergence of a broad zero-bias conductance peak with subgap features.

Unusual magnetic field dependence of tunneling features.

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$_{4}$.