  We consider tunneling transport between two parallel graphene sheets where
one is a single-layer sample and the other one a bilayer. In the presence of an
in-plane magnetic field, the interplay between combined energy and momentum
conservation in a tunneling event and the distinctive chiral nature of charge
carriers in the two systems turns out to favor tunneling of electrons from one
of the two valleys in the graphene Brillouin zone. Adjusting the field strength
enables manipulation of the valley polarization of the current, which reaches
its maximum value of 100% concomitantly with a maximum of the tunneling
conductance.
