  Owing to the coupling between open Fermi arcs on opposite surfaces,
topological Dirac semimetals exhibit a new type of cyclotron orbit in the
surface states known as Weyl orbit. Here, by lowering the carrier density in
Cd3As2 nanoplates, we observe a crossover from multiple- to single-frequency
Shubnikov-de Haas (SdH) oscillations when subjected to out-of-plane magnetic
field, indicating the dominant role of surface transport. With the increase of
magnetic field, the SdH oscillations further develop into quantum Hall state
with non-vanishing longitudinal resistance. By tracking the oscillation
frequency and Hall plateau, we observe a Zeeman-related splitting and extract
the Landau level index as well as sub-band number. Different from conventional
two-dimensional systems, this unique quantum Hall effect may be related to the
quantized version of Weyl orbits. Our results call for further investigations
into the exotic quantum Hall states in the low-dimensional structure of
topological semimetals.
