  Cadmium arsenide (Cd3As2) is one of the first materials to be discovered to
belong to the class of three-dimensional topological semimetals. Reported room
temperature crystal structures of Cd3As2 reported differ subtly in the way the
Cd vacancies are arranged within its antifluorite-derived structure, which
determines if an inversion center is present and if Cd3As2 is a Dirac or Weyl
semimetal. Here, we apply convergent beam electron diffraction (CBED) to
determine the point group of Cd3As2 thin films grown by molecular beam epitaxy.
Using CBED patterns from multiple zone axes, high-angle annular dark-field
images acquired in scanning transmission electron microscopy, and Bloch wave
simulations, we show that Cd3As2 belongs to the tetragonal 4/mmm point group,
which is centrosymmetric. The results show that CBED can distinguish very
subtle differences in the crystal structure of a topological semimetal, a
capability that will be useful for designing materials and thin film
heterostructures with topological states that depend on the presence of certain
crystal symmetries.
