T. Golod, A. Rydh, V. M. Krasnov, I. Marozau, M. A. Uribe-Laverde, D. K. Satapathy, Th. Wagner, C. Bernhard
We study epitaxial all-perovskite superconductor/feromagnetic insulator/superconductor tunnel junctions. A pronounced step in the current-voltage characteristics is observed in the superconducting state that closely resembles the sum-gap singularity in conventional superconducting tunnel junctions. However, the voltage of the step of $\sim 1$ V is more than an order of magnitude larger than the superconducting energy gap. The step is attributed to inelastic tunneling above the spin-polaron mobility edge in the LaMnO$_{3+\delta}$ in resonance with sharp superconducting singularities in the density of states of YBa$_2$Cu$_3$O$_{7-x}$. A significant photon emission at the step is detected. It is argued that such inelastic resonant tunneling improves the spin-filtering effect by the ferromagnetic insulator.
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http://arxiv.org/abs/1206.2053
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