Critical current in superconducting quantum point contacts

The quantization of the critical current I-c in a quantum point contact is studied on varying the number of free channels (varying the constriction width d(0) in 2DEG). It is shown that the shape of the quantum I-c is not universal and depends on the parameters of the contact, in particular, on the properties of the 2DEG-S boundaries. Because of the effect of normal reflection from the S-2DEG boundaries, the quantum critical current nonmonotonically depends on d(0) and may have a resonance structure. If E-F coincides with a quasi-stationary level of the square potential well formed by the contact walls, the critical current has a local maximum (resonance) equal (in the first channel) to the ratio of the electron charge to its time of travel through the contact. The critical current at the maximum is determined by the lowest positive Andreev level (for the phase difference pi). (C) 2000 MAIK "Nauka/Interperiodica".