  A lateral Josephson junction in which the surface of a 3D topological
insulator serves as the weak link should support topologically protected
excitations related to Majorana fermions. The resulting $4\pi$-periodic
current-phase relationship could be detected under high-frequency excitation by
the suppression of odd Shapiro steps. Here, we demonstrate such devices through
the self-formation of a Pd-Te superconducting layer from a telluride
topological insulator, and observe suppressed first and third Shapiro steps.
Other devices, including those where the Pd-Te layer is bolstered by an
additional Al layer, show no suppression of Shapiro steps, a difference
supported by simulations. Though we rule out the known trivial causes of
suppressed Shapiro steps in our devices, we nevertheless argue that
corroborating measurements and disorder-aware theoretical descriptions of these
systems are needed before confidently claiming the observation of Majorana
states.
