Quasiparticle charge imbalance, first-order phase transition and quantum criticality in ferromagnet/superconductor/ferromagnet double-tunnel junctions

摘要

Spin-dependent transport in ferromagnet/superconductor/ferromagnet double-tunnel junctions is revisited by taking both the spin and quasiparticle charge imbalances into account. It is shown that even a small quasiparticle charge imbalance can lead to remarkable changes of the superconducting and transport properties. In particular, it is found that a first-order phase transition from an inhomogeneous superconducting state to the normal state will take place in both the antiparallel and parallel alignments of magnetizations, as the bias voltage is increased to a critical value. A quantum critical point is specified.