Subgap magnetotransport in Pb/LaCaMnO point contacts

Andreev reflection spectroscopy has been used to probe mutual influence of superconductivity and ferromagnetism in contacts of a low-temperature superconductor ( S), Pb, and a half-metallic ferromagnet, La0.65Ca0.35MnO3 ( LCMO). In the contacts, which we distinguish as proximity-affected ones, a few unusual effects have been detected: i) a spectacular drop in the resistance of the contacts at the onset of the Pb superconductivity; ii) excess current and doubling of the normal-state conductance; iii) subharmonic gap structure; and iv) the ratio of the single-particle gap to the Pb superconducting transition temperature is anomalously large. Microscopically, our results can most reasonably be explained assuming a conversion from spin singlet pairs to spin triplets at the S/LCMO interface and a long-range proximity effect.