Spin-Triplet Superconductivity inSr2RuO4Probed by Andreev Reflection

The superconducting gap function of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ was investigated by means of quasiparticle reflection and transmission at the normal conductor-superconductor interface of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4-\mathrm{P}\mathrm{t}$ point contacts. We found two distinctly different types of $\mathrm{dV}/\mathrm{dI}$ 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 ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$.