We demonstrate that a supercurrent can flow through a high-mobility two-dimensional electron gas (2DEG) between two superconducting contacts 1 μm apart. The ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs channel length is over 10 times the proximity-effect-induced coherence length in the semiconductor, and electrons travel ballistically between the contacts. The supercurrent is destroyed when the mobility of the 2DEG is reduced by electron-beam irradiation, suggesting that the supercurrent results from coherent Andreev reflection and ballistic transport between the superconducting electrodes.

DOI:https://doi.org/10.1103/PhysRevB.50.8118