Ballistic SNS sandwich as a Josephson junction

TL;DR

This paper develops a new theoretical model for ballistic SNS sandwiches, revealing that they can exhibit Josephson effects without proximity effects and possess unique properties like arbitrary ground state phase and unchanged supercurrent at high temperatures.

Contribution

It introduces a revised theory accounting for charge conservation and gap incommensurability, showing that 1D ballistic SNS sandwiches can have any ground state phase and are not weak links at zero temperature.

Findings

Ground state phase can vary from 0 to π in 1D cases.

Supercurrent suppression at high temperatures does not occur in 1D.

Ballistic SNS sandwiches are not weak links at zero temperature.

Abstract

The paper develops the theory of the ballistic SNS sandwich, in which the Josephson effect exists without the proximity effect. The theory takes into account restrictions imposed by the charge conservation law and the incommensurability of the superconducting gap with the Andreev level energy spacing. This resulted in revisions of some conclusions of previous works. In the one-dimensional case the Josephson phase of the ground state of the ballistic SNS sandwich is not necessarily zero but may have any value from 0 to $\pi$. If this value is $\pi$ this is a $\pi$ junction, which was well known before. The suppression of the supercurrent at temperatures on the order or higher than the Andreev level energy spacing, which was predicted in previous investigations, does not take place in the one-dimensional case. At zero temperature the ballistic SNS sandwich of any dimensionality is not a weak link. This leads to unusual properties: the absence of the Josephson plasma mode localized at the normal layer and the Meisner effect with the same London penetration depth in the normal and the superconducting layers.