Superconducting coupling across a spin-filtering manganite tunnel barrier with magnetic disorder

Ferromagnetic insulator Josephson junctions consisting of Nb/Au/Pr_0.8Ca_0.2MnO₃/La_1.85Sr_0.15CuO₄ layers were fabricated. Non-linear current-voltage characteristics suggest the presence of superconducting coupling between the Nb/Au and La_1.85Sr_0.15CuO₄ layers across a ferromagnetic Pr_0.8Ca_0.2MnO₃ tunnel barrier. Tunneling spectra showed clear conductance peaks due to quasi-particle tunneling. Superconducting gap energies determined from the tunneling spectra were consistent with the temperature dependence of the critical current of the junctions. We argue that magnetic inhomogeneity in the ultrathin tunnel barrier plays a role in linking the superconducting states in Nb/Au and La_1.85Sr_0.15CuO₄.