On the Sarma-Type Phase Transitions in Ferromagnet/Superconductor/Ferromagnet Tunneling Junctions with Highly Spin-Polarized Ferromagnets

In the ferromagnet/superconductor/ferromagnet double tunneling junctions, the spin-polarized tunneling current in the antiparallel alignment of the magnetization induces spin imbalance in the superconductor, which has a pair breaking effect depressing superconductivity in the same way that the Zeeman effect does in the paramagnetic limit. In particular, it is shown that when the ferromagnets are highly spin polarized, the strong spin imbalance may lead to a first-order phase transition from the superconducting phase to the normal phase at low temperature and low bias voltage. This phase transition accompanies a large discontinuous drop in superconducting gap parameter bring in distinctive features in low energy transport.