  Hybrid structures between conventional, s-wave superconductors and
two-dimensional topological insulators (2D TIs) are a promising route to
topological superconductivity. Here, we investigate planar Josephson junctions
fabricated from hybrid structures that use thin films of cadmium arsenide
(Cd3As2) as the 2D TI material. Measurements of superconducting interference
patterns in a perpendicular magnetic field are used to extract information
about the spatial distribution of the supercurrent. We show that the
interference patterns are distinctly different in junctions with and without
mesa-isolation, respectively. In mesa-defined junctions, the bulk of the 2D TI
appears to be almost completely shunted by supercurrent flowing along the
edges, while the supercurrent is much more uniform across the junction when the
Cd3As2 film extends beyond the device. We discuss the possible origins of the
observed behaviors.
