Influence of a single defect on the conductance of a tunnel point contact between a normal metal and a superconductor

TL;DR

This paper theoretically analyzes how a single defect affects the conductance of a normal metal-superconductor tunnel point contact, revealing oscillatory behavior influenced by defect position and bias energy.

Contribution

It provides analytical expressions for conductance oscillations caused by a defect, considering its position in either the normal metal or superconductor.

Findings

Conductance oscillations depend on defect position and bias energy.

Oscillation amplitude increases near the superconductor's gap energy.

Spatial variation of the order parameter near the surface is characterized.

Abstract

We have investigated theoretically the conductance of a Normal-Superconductor point-contact in the tunnel limit and analyzed the quantum interference effects originating from the scattering of quasiparticles by point-like defects. Analytical expressions for the oscillatory dependence of the conductance on the position of the defect are obtained for the defect situated either in the normal metal, or in the superconductor. It is found that the amplitude of oscillations significantly increases when the applied bias approaches the gap energy of the superconductor. The spatial distribution of the order parameter near the surface in the presence of a defect is also obtained.