  Topological superconductivity is an exotic state of matter that supports
Majorana zero-modes, which are surface modes in 3D, edge modes in 2D or
localized end states in 1D. In the case of complete localization these Majorana
modes obey non-Abelian exchange statistics making them interesting building
blocks for topological quantum computing. Here we report superconductivity
induced into the edge modes of semiconducting InAs/GaSb quantum wells, a
two-dimensional topological insulator. Using superconducting quantum
interference, we demonstrate gate-tuning between edge-dominated and
bulk-dominated regimes of superconducting transport. The edge-dominated regime
arises only under conditions of high-bulk resistivity, which we associate with
the 2D topological phase. These experiments establish InAs/GaSb as a robust
platform for further confinement of Majoranas into localized states enabling
future investigations of non-Abelian statistics.
