  We propose a device in which a sheet of graphene is coupled to a Weyl
semimetal, allowing for the physical access to the study of tunneling from
two-dimensional to three dimensional massless Dirac fermions. Due to the
reconstructed band structure, we find that this device acts as a robust valley
filter for electrons in the graphene sheet. We show that, by appropriate
alignment, the Weyl semimetal draws away current in one of the two graphene
valleys while allowing current in the other to pass unimpeded.
  In contrast to other proposed valley filters, the mechanism of our proposed
device occurs in the bulk of the graphene sheet, obviating the need for
carefully shaped edges or dimensions.
