Negative critical currents in single-channel Josephson junctions

TL;DR

This paper demonstrates that negative critical currents can naturally occur in single-channel Josephson junctions, with the sign depending on electron occupancy, revealing a fundamental aspect of quantum transport in these systems.

Contribution

It provides a theoretical analysis showing how the critical current sign alternates with electron number, highlighting a novel quantum effect in single-channel Josephson junctions.

Findings

Negative critical currents occur in single-channel Josephson junctions.

The sign of the critical current depends on the electron number parity.

Negative critical currents appear even at large electron numbers for odd occupancy.

Abstract

We argue that negative critical currents arise generically in Josephson junctions formed by single channel conductors. Specifically, we theoretically study the Josephson coupling between two superconducting leads connected by a one-dimensional conductor in the Coulomb blockade regime. We show that in the clean regime the sign of the critical current alternates with the number of electrons in the normal region. For odd occupancy the critical current is negative even when the number of electrons on the conductor is large.