  The introduction of superconductivity to the Dirac surface states of a
topological insulator leads to a topological superconductor, which may support
topological quantum computing through Majorana zero modes. The development of a
scalable material platform is key to the realization of topological quantum
computing. Here we report on the growth and properties of high-quality
(Bi,Sb)2Te3/graphene/gallium heterostructures. Our synthetic approach enables
atomically sharp layers at both hetero-interfaces, which in turn promotes
proximity-induced superconductivity that originates in the gallium film. A
lithography-free, van der Waals tunnel junction is developed to perform
transport tunneling spectroscopy. We find a robust, proximity-induced
superconducting gap formed in the Dirac surface states in 5-10 quintuple-layer
(Bi,Sb)2Te3/graphene/gallium heterostructures. The presence of a single
Abrikosov vortex, where the Majorana zero modes are expected to reside,
manifests in discrete conductance changes. The present material platform opens
up opportunities for understanding and harnessing the application potential of
topological superconductivity.
