Andreev spectroscopy of point contacts between a low-temperature superconductor and manganite

Abstract

Andreev reflection in contacts between a low-temperature superconductor (Pb or MgB2) and the manganite La0.65Ca0.35MnO3 (LCMO) is investigated. In the majority of cases behavior typical of superconductor/half-metallic ferromagnet contacts is observed: an excess voltage Vexc and suppression of the contact conductance G(V)=dI(V)∕dV in the region of voltages e∣V∣≤ΔS, where ΔS is the energy gap of the injector. However, some of the contacts demonstrate an increase of the conductance and an excess current Iexc on the current–voltage characteristic of the contact at e∣V∣≤ΔS. The character of the dI(V)∕dV curves observed for those contacts corresponds to Andreev spectrum of a superconductor with an energy gap much larger than the injector gap ΔS. It is assumed that in contacts of the latter type, specific conditions prevail whereby the penetration of Cooper pairs into the manganite from an electrode with a singlet order parameter induces in the surface region of the manganite a superconducting state with a triplet type of correlations.