  The prospect of coupling a two-dimensional (2D) semiconductor heterostructure
to a superconductor opens new research and technology opportunities, including
fundamental problems in mesoscopic superconductivity, scalable superconducting
electronics, and new topological states of matter. For instance, one route
toward realizing topological matter is by coupling a 2D electron gas (2DEG)
with strong spin-orbit interaction to an s-wave superconductor. Previous
efforts along these lines have been hindered by interface disorder and unstable
gating. Here, we report measurements on a gateable InGaAs/InAs 2DEG with
patterned epitaxial Al, yielding multilayer devices with atomically pristine
interfaces between semiconductor and superconductor. Using surface gates to
form a quantum point contact (QPC), we find a hard superconducting gap in the
tunneling regime, overcoming the soft-gap problem in 2D
superconductor-semiconductor hybrid systems. With the QPC in the open regime,
we observe a first conductance plateau at 4e^2/h, as expected theoretically for
a normal-QPC-superconductor structure. The realization of a hard-gap
semiconductor-superconductor system that is amenable to top-down processing
provides a means of fabricating scalable multicomponent hybrid systems for
applications in low-dissipation electronics and topological quantum
information.
