The critical supercurrent $I_c$ carried by a short (0.3 to $0.8\hspace{0.5em}\mu \mathrm{m})$ ballistic two-dimensional InAs-based electron gas between superconducting niobium electrodes is studied. In relating the maximum value to the resistance of the weak link in the normal state $R_n$ a much lower value is found than theoretically expected for a ballistic system. The energy scale which characterizes the observed temperature dependence is comparable to the energy associated with the product of $I_c$ and $R_n.$ We point out that although the transport between the electrodes is ballistic, in the InAs underneath the superconducting electrodes the transport is diffusive, an experimental case which has not yet been studied theoretically.

• Received 4 January 1999

DOI:https://doi.org/10.1103/PhysRevB.60.13135