The phase-dependent linear conductance of a superconducting quantum point contact

TL;DR

This paper derives an exact expression for the phase-dependent linear conductance of a superconducting quantum point contact, revealing nonperturbative effects and phase behavior that align with experimental observations.

Contribution

It provides a nonperturbative calculation of conductance that corrects standard tunnel theory and captures phase-dependent effects at low temperatures.

Findings

Nonperturbative conductance expression derived

Standard tunnel theory results are challenged

Predicted phase dependence matches experimental data

Abstract

The exact expression for the phase-dependent linear conductance of a weakly damped superconducting quantum point contact is obtained. The calculation is performed by summing up the complete perturbative series in the coupling between the electrodes. The failure of any finite order perturbative expansion in the limit of small voltage and small quasi-particle damping is analyzed in detail. In the low transmission regime this nonperturbative calculation yields a result which is at variance with standard tunnel theory. Our result predicts the correct sign of the quasi-particle pair interference term and exhibits an unusual phase-dependence at low temperatures in qualitative agreement with the available experimental data.