Spin- and valley-dependent negative magnetoresistance in a ferromagnetic MoS2 junction with a quantum well

We studied the spin and valley transports and magnetoresistance effect in a MoS2 junction with a quantum well inserted between the gate voltage and the ferromagnetic MoS2, which can apply generally to other transition metal dichalcogenides with the same crystal structure. In the absence of a quantum well, the broken inversion symmetry and spin-orbit coupling for MoS2 could give rise to a fully spin- and valley-polarized conductance for the parallel configuration, while there is no spin and valley polarization for the antiparallel configuration. The general condition of pure polarization and the position of resonant conductance are achieved. The magnetoresistance is positive and oscillates with the gate voltage. Dramatically, the presence of a quantum well can lead to the formation of spin-polarized quantum well states. As a result, the conductances for opposite spin and valley indices have a steady phase shift, making them oscillate in antiphase with the well width. Therefore, the high spin and valley polarization could be obtained for the antiparallel and parallel configurations. In particular, the spin-polarized quantum well states directly result in negative polarization and negative magnetoresistance.