Valley filtering using electrostatic potentials in bilayer graphene
  Propagation of an electron wave packet through a quantum point contact (QPC) defined by electrostatic gates in bilayer graphene is investigated. The gates provide a bias between the layers, in order to produce an energy gap. If the gates on both sides of the contact produce the same bias, steps in the electron transmission probability are observed, as in the usual QPC. However, if the bias is inverted on one of the sides of the QPC, only electrons belonging to one of the Dirac valleys are allowed to pass, which provides a very efficient valley filtering. 
D. R. da Costa, A. Chaves, S. H. R. Sena, G. A. Farias, and F. M.   Peeters
cond-mat.mes-hall