# Observation of superconducting gap spectra of long-range proximity effect in Au/SrTiO$_3$/SrRuO$_3$/Sr$_2$RuO$_4$ tunnel junctions

## TL;DR

This study demonstrates the induction of a superconducting minigap in a ferromagnetic SrRuO$_3$ layer via a spin-triplet superconductor, providing evidence for $p$-wave Cooper pair penetration and advancing understanding of the spin-triplet proximity effect.

## Contribution

It provides experimental evidence and theoretical support for $p$-wave superconducting correlations in a ferromagnet induced by a spin-triplet superconductor.

## Key findings

- Observation of a superconducting minigap in SrRuO$_3$
- Confirmation of $p$-wave dominance in induced superconductivity
- Support for the spin-triplet proximity effect theory

## Abstract

We observe an unconventional superconducting minigap induced into a ferromagnet SrRuO$_3$ from a spin-triplet superconductor Sr$_2$RuO$_4$ using a Au/SrTiO$_3$/SrRuO$_3$/Sr$_2$RuO$_4$ tunnel junction. Voltage bias differential conductance of the tunnel junctions exhibits V-shaped gap features around zero bias, corresponding to a decrease in the density-of-states with an opening of a superconducting minigap in SrRuO$_3$. Observation of a minigap at a surface of a 15~nm thick SrRuO$_3$ layers confirms the spin-triplet nature of induced superconductivity. The shape and temperature dependence of the gap features in the differential conductance indicate that the even-frequency $p$-wave correlations dominate, over odd-frequency $s$-wave correlations. Theoretical calculations support this $p$-wave scenario. Our work provides the density-of-states proof for $p$-wave Cooper pair penetration in a ferromagnet and significantly put forward our understanding of the $p$-wave spin-triplet proximity effect between spin-triplet superconductors and ferromagnets.