We have determined the individual transmission coefficients of Al quantum point contacts containing up to six conduction channels. The determination is based on a comparison of the highly nonlinear current-voltage characteristics in the superconducting state with the predictions of the theory for a single channel superconducting contact. We find that at least two channels contribute to the transport even for contacts with conductance lower than the conductance quantum.

• Received 4 February 1997

DOI:https://doi.org/10.1103/PhysRevLett.78.3535