Design of Josephson diode based on magnetic impurity

TL;DR

This paper proposes a theoretical mechanism for a superconducting diode effect using magnetic impurities in Josephson junctions, which does not require unconventional superconductors or external magnetic fields.

Contribution

It introduces a universal design for a superconducting diode based on magnetic impurities, avoiding the need for spin-orbit coupling or chirality.

Findings

The superconducting diode effect exists in the proposed system.

The effect is tunable across a wide parameter space.

The design is simple, requiring only magnetic impurities and conventional superconductors.

Abstract

We theoretically propose a mechanism to realize the superconducting diode effect (SDE): The current can generate a magnetic field, affecting the magnetic moment of magnetic impurity. When the connection region of the Josephson junction is coupled with the magnetic impurity, the supercurrents in positive and negative directions have different influences on the magnetic moment. This results in a phenomenon that the critical supercurrents in these opposite directions are unequal, which is called SDE. We model the Josephson connection region by a quantum dot. Then the critical supercurrents are investigated by the non-equilibrium Green's function method, and we carry out a detailed symmetry analysis on the supercurrent relations. The calculation results confirm that the SDE does exist in this system. Besides, the SDE is significant in a wide parameter space and can be effectively adjusted in various ways. Our design only demands a magnetic impurity and conventional superconductors. The unconventional finite-momentum Cooper pair and spin-orbit coupling are not required, and there is also no need for the existence of chirality or an external magnetic field. Our work provides a universal device structure for the development of superconducting electronics.