Long range Josephson coupling across a half metallic ferromagnet at high temperatures*

Ferromagnetism and singlet superconductivity are antagonistic phenomena. At interfaces with a ferromagnet, the singlet pairing amplitude decays over nanometric distances. In presence of magnetization inhomogeneities, however, equal spin triplet Cooper pairs can be generated, allowing the coupling of superconductors in Josephson junctions across magnetic barriers over much longer distances. We demonstrate extremely long range high-temperature Josephson coupling across the half-metallic manganite La_0.7Sr_0.3MnO₃ combined with the superconducting cuprate YBa₂Cu₃O₇. This is shown in planar junctions which display the hallmarks of Josephson physics: critical current oscillations (Fraunhofer pattern) and quantum phase locking under microwave excitation (Shapiro steps). The conjunction of quantum coherent transport and full spin polarization can bring unique opportunities for the practical realization of superconducting spintronics, and novel strategies in quantum computing.