Tunneling magnetoresistance effect in ferromagnet/quantum dot/superconductor junctions

We analyze the charge transport in a ferromagnet/quantum dot/superconductor system assuming an exchange-type interaction on the quantum dot. The nonequilibrium Green’s function method is employed to calculate the tunneling charge conductance. When the ferromagnetic lead is in the half-metallic limit, the key mechanism governing the low-energy charge transport of this hybrid structure is the so-called same-spin-band Andreev reflection, in which the incident electron and the Andreev reflected hole belong to the same spin-band. The same-spin-band Andreev reflection depends sensitively on the relative angle θθ between the exchange field in ferromagnetic lead and the exchange field in quantum dot, and may induce giant magnetoresistance effect in the low temperature regime.

► We study the TMR effect in FM/QD/SC system systematically.
► The same-spin-band AR dominates the subgap transport here.
► TMR ratio larger than 105% is obtained at low temperatures.