Long range unconventional Josephson effect across a half metallic ferromagnet

Jacobo Santamaria

The Josephson effect results from the coupling of two superconductors across a non- superconducting spacer to yield a quantum coherent state. In ferromagnets, singlet (opposite- spin) Cooper pairs decay over very short distances, and thus Josephson coupling requires a nanometric spacer. This is unless equal-spin triplet pairs are generated which, theoretically, can couple superconductors across much longer distances. Despite many experimental hints of triplet superconductivity, long range triplet Josephson effects have remained elusive. In this talk I will discuss a micron-range Josephson coupling across the half-metallic ferromagnet
La0.7Sr0.3MnO3 combined with the high-temperature superconductor YBa2Cu3O7 in planar junctions. These display the Josephson physics’ hallmarks: critical current oscillations due to flux quantization and quantum phase locking under microwave excitation. The marriage of high- temperature quantum coherent transport and full spin polarization brings unique opportunities for the practical realization of superconducting spintronics, and enables novel strategies for quantum computing.