Critical currents in ballistic two-dimensional InAs-based superconducting weak links

The critical supercurrent I-c carried by a short (0.3 to 0.8 mu m) ballisti c two-dimensional InAas-based electron gas between superconducting niobium electrodes is studied. In relating the maximum value to the resistance of t he weak link in the normal state R-n, a much lower value is found than theo retically expected for a ballistic system. The energy scale which character izes the observed temperature dependence is comparable to the energy associ ated with the product of I-c and R-n. We point out that although the transp ort between the electrodes is ballistic, in the InAs underneath the superco nducting electrodes the transport is diffusive, an experimental case which has not yet been studied theoretically. [S0163-1829(99)09741-6].