Andreev reflexion at nanocontacts of superconducting AuIn2 with copper

We investigated superconducting AuIn₂ by point-contact spectroscopy. Andreev reflexion was observed with nearly full excess current at contact sizes down to 0.15 nm. This implies, together with a large superconducting coherence length of 11 μm, almost ideal retroreflectivity. At the onset of lateral confinement of the ballistic electrons the Andreev-derived spectra broaden dramatically due to inelastic scattering at defects or the strain field near the contact. Lateral confinement does not suppress Andreev reflexion.