Magnetic proximity effect and superconducting triplet correlations at the interface of cuprate superconductor and an oxide spin-valve
Journal article, 2016
The heterostructure comprising a cuprate superconductor YBa2Cu3O7-? and a spin-valve of ruthenate/ manganite (SrRuO3/La0.7Sr0.3MnO3) has been studied by SQUID magnetometry, ferromagnetic resonance, and neutron reflectometry. It was shown that magnetic moment arises in a superconducting part of heterostructure while in spin-valve magnetic moment is suppressed. The obtained experimental value of characteristic penetration depth of magnetic moment into superconductor greatly exceeds the superconductor coherence length the cuprate superconductor indicating the dominance of mechanism of induced magnetic moment from Cu atoms. The mesa-structures made with an addition niobium superconducting electrode deposited on top of heterostructure showed superconducting current (dc Josephson effect) when thickness of interlayer was much greater than the coherence lengths of ferromagnetic materials of spin-valve. The maximum of the dependence of critical current density vs. thicknesses of magnetic materials corresponds to their coherence lengths, that is consistent with the theoretical predictions for the case of spin-triplet pairing. The superconducting current is observed at magnetic fields by two orders greater than the value of magnetic field corresponding to the occurrence of one magnetic flux quantum in the mesa-structure. The ratio of the second harmonic in current-phase relation of the superconducting current of mesa structure to the first harmonic, obtained from measurements of Shapiro step amplitudes under microwaves did not exceed 50%.