Local triplet superconductivity of La0.65Ca0.35MnO3-X point contacts (X=Pb,MgB2)

Microconstrictions between spin-singlet superconductor, Pb or MgB2, tip and half-metallic ferromagnet, La0.65Ca0.35MnO3 (LCMO), plate have been realized by means of a point-contact inset. Measurements of the current-voltage characteristics and of the dynamic conductance G(V) versus bias have been performed to probe mutual influence of superconductivity and half-metallic ferromagnetism. In the contacts, which we distinguish as proximity affected ones, a few principal effects have been observed. Namely, with decreasing temperature, a spectacular drop of the contact's resistance has been detected with an onset of the Pb or MgB2 superconductivity; for small voltages, an excess current and doubling of the normal-state conductance have also been found. We conclude that the underlying physical explanations for these results are the conversion from spin-singlet pairs to spin-triplet ones at the Pb (MgB2)/LCMO interface and a long-range proximity induced superconductivity of LCMO. Superconducting state of LCMO is also supported by the observation of the coherent multiple Andreev reflections (subharmonic gap resonances). We also found that the character of G(V) vs voltage dependence corresponds to that for the induced superconducting energy gap of LCMO much larger than that of Pb or MgB2. All specific characteristics of proximity affected contacts suggest that the local triplet superconducting fluctuations are essentially sustained in LCMO and the singlet superconductors only fix the phase coherency of a superconducting state.