Tunneling conductance and magnetoresistance in topological insulator Fi/I/Fi/d-wave superconductor junctions

We investigate the tunneling conductance and tunneling magnetoresistance (TMR) in topological insulator ferromagnetic insulator/insulator/ferromagnetic insulator/d-wave superconductor (Fi/I/Fi/d-wave SC) junction, by applying the Blonder-Tinkham-Klapwijk approach. We find that the multiple scatterings in the middle ferromagnetic layer cause the conductance to exhibit an oscillatory behavior as a function of barrier strength even in the case where there is a large Fermi surface mismatch between ferromagnetic and superconductor regions. We find also that the conductance in antiparallel magnetization configuration can be larger than that in the parallel one, depending on the value of barrier strength. This, together with the magnetically induced phase shift of the antiparallel conductance relative to the parallel conductance, leads to a huge negative tunneling magnetoresistance.