  A new class of multilayered functional materials has recently emerged in
which the component atomic layers are held together by weak van der Waals
forces that preserve the structural integrity and physical properties of each
layer. An exemplar of such a structure is a transistor device in which
relativistic Dirac Fermions can resonantly tunnel through a boron nitride
barrier, a few atomic layers thick, sandwiched between two graphene electrodes.
An applied magnetic field quantises graphene's gapless conduction and valence
band states into discrete Landau levels, allowing us to resolve individual
inter-Landau level transitions and thereby demonstrate that the energy,
momentum and chiral properties of the electrons are conserved in the tunnelling
process. We also demonstrate that the change in the semiclassical cyclotron
trajectories, following a tunnelling event, is a form of Klein tunnelling for
inter-layer transitions.
