The Andreev spectroscopy of low-temperature superconductor-manganite point contacts

The Andreev reflection in low-temperature superconductor (Pb or MgB₂)—manganite La_0.65Ca_0.35MnO₃ (LCMO) contacts have been investigated. In most cases, typical of superconductor/half-metallic ferromagnet contacts for a voltage range e|V| ≤ D_S, where D_S is the energy gap of the superconducting injector, an excess voltage V_exc and a suppression of the contact conductivity, G(V) = dI(V)/dV, are observed. However, a number of contacts at e|V| ≤ DS, reveal an increase in conductivity and an excess current in the current-voltage dependences. The behavior of the observed dI(V)/dV dependence in such contacts corresponds to Andreev spectra for a superconductor with an energy gap much larger than that of the injector D_S. It is suggested that in such contacts the specific conditions are realized due to which the Cooper pairs penetration from the electrode with a singlet order parameter into the manganite induces a superconducting state with triplet type correlations in the manganite surface region.

Key words: proximity effect, Andreev reflection, half-metallic ferromagnet, contact spectroscopy, triplet superconductivity.

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