Quantized conductance in semiconductor-superconductor-junction quantum point contacts

We present a numerical calculation of the quantized point contact conductance in a normal-metal-superconductor (NS) junction in the presence of disorder. It is shown that the flared geometry of the constriction improves the quantization. Random potential or interface roughness is found to destroy the quantization. The disorder induced suppression of the conductance is less significant when the constriction narrows due to retroreflection at the NS interface. The conductance approaches the value of normal point contacts when a magnetic field is applied. A good agreement of the magnetic-field dependence with an experiment is obtained.