Nonequilibrium superconductivity under spin-polarized quasiparticle currents in perovskite ferromagnet-insulator-superconductor heterostructures

We report phenomena manifesting nonequilibrium superconductivity induced by spin-polarized quasiparticles in perovskite ferromagnet-insulator-superconductor (F-I-S) heterostructures. Measurements of the critical current Jc, using a pulsed current technique to minimize Joule heating, reveal a monotonic increase with increasing insulator thickness; and for F-I-S with thin insulating barriers, a slight increase in Jc is observed under small injection currents Iₘ from the ferromagnet, followed by a strong suppression of Jc under large Iₘ. In contrast, no effect of injection on Jc can be detected in the N-I-S control sample (N: nonmagnetic metal). The spin diffusion time and length in cuprate superconductors are also estimated and compared with our experimental results.