Tunneling Properties at the Interface between Superconducting Sr₂RuO₄ and a Ru Microinclusion

Abstract

We have investigated the magnetic field and temperature dependence of the tunneling spectra of the eutectic system Sr₂RuO₄–Ru. Electric contacts to individual Ru lamellae embedded in Sr₂RuO₄ enable the tunneling spectra at the interface between ruthenate and a Ru microinclusion to be measured. A zero bias conductance peak (ZBCP) was observed in the bias voltage dependence of the differential conductance, suggesting that Andreev bound states are present at the interface. The ZBCP starts to appear at a temperature well below the superconducting transition temperature. The onset magnetic field of the ZBCP is also considerably smaller than the upper critical field when the magnetic field is parallel to the ab-plane. We propose that the difference between the onset of the ZBCP and the onset of superconductivity can be understood in terms of the existence of the single-component state predicted by Sigrist and Monien.