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-supercon ductor (F-I-S) heterostructures. Measurements of the critical current J(c), using a pulsed current technique to minimize Joule heating, reveal a monot onic increase with increasing insulator thickness, and for F-I-S with thin insulating barriers, a slight increase in J(c) is observed under small inje ction currents I-m from the ferromagnet, followed by a strong suppression o f J(c) under large I-m. In contrast, no effect of injection on J(c) can be detected in the N-I-S control sample (N: nonmagnetic metal). The spin diffu sion time and length in cuprate superconductors are also estimated and comp ared with our experimental results. [S0163-1829(99)05638-6].