Spin-triplet superconductivity in Sr$_2$RuO$_4$ probed by Andreev reflection

TL;DR

This study uses Andreev reflection measurements at Sr$_2$RuO$_4$-Pt interfaces to provide strong evidence for spin-triplet superconductivity in Sr$_2$RuO$_4$, revealing distinct spectral features linked to interface transparency.

Contribution

The paper demonstrates that quasiparticle reflection spectra support the spin-triplet pairing symmetry in Sr$_2$RuO$_4$, advancing understanding of its unconventional superconductivity.

Findings

Observation of two distinct spectral types consistent with different interface transparencies.

Spectral features support spin-triplet pairing symmetry.

Temperature dependence reinforces the triplet superconductivity hypothesis.

Abstract

The superconducting gap function of Sr$_2$RuO$_4$ was investigated by means of quasiparticle reflection and transmission at the normal conductor-superconductor interface of Sr$_2$RuO$_4$-Pt point contacts. We found two distinguishly different types of $dV/dI$ vs $V$ spectra either with a double-minimum structure or with a zero-bias conductance anomaly. Both types of spectra are expected in the limit of high and low transparency, respectively, of the interface barrier between a normal metal and a spin-triplet superconductor. Together with the temperature dependence of the spectra this result strongly supports a spin-triplet superconducting order parameter for Sr$_2$RuO$_4$.