  Two-dimensional states in confined thin films of the three-dimensional Dirac
semimetal Cd3As2 are probed by transport and capacitance measurements under
applied magnetic and electric fields. The results establish the two-dimensional
Dirac electronic spectrum of these states. We observe signatures of p-type
conduction in the two-dimensional states as the Fermi level is tuned across
their charge neutrality point and the presence of a zero energy Landau level,
all of which indicate topologically non-trivial states. The resistance at the
charge neutrality point is approximately h/e2 and increases rapidly under the
application of a magnetic field. The results open many possibilities for
gate-tunable topological devices and for the exploration of novel physics in
the zero energy Landau level.
