  We investigate the quantum transport properties of multichannel nanoribbons
made of materials described by the Dirac equation, under an in-plane magnetic
field. In the low energy regime, positive and negative finger-gate potentials
allow the electrons to make intra-subband transitions via hole-like or
electron-like quasibound states (QBS), respectively, resulting in dips in the
conductance. In the high energy regime, double dip structures in the
conductance are found, attributed to spin-flip or spin-nonflip inter-subband
transitions through the QBSs. Inverting the finger-gate polarity offers the
possibility to manipulate the spin polarized electronic transport to achieve a
controlled spin-switch.
