Field-free Josephson diode effect in altermagnet/normal metal/altermagnet junctions

TL;DR

This paper proposes a highly efficient, field-free Josephson diode using altermagnets with zero net magnetization, enabling nonreciprocal supercurrent flow without external magnetic fields, suitable for dissipationless superconducting devices.

Contribution

It introduces a novel Josephson diode based on altermagnets that achieves high efficiency without external magnetic fields, avoiding magnetic cross-talk in superconducting circuits.

Findings

Efficiency exceeds 40% and remains stable under parameter variations.

Diode efficiency can be inverted by adjusting the relative orientation angle.

Symmetry analysis explains the current-phase relation and diode behavior.

Abstract

The field-free and highly efficient diodes with the nonreciprocity of supercurrent are believed to be the core block of the superconducting computing devices without dissipation. In this paper, we propose a Josephson diode based upon altermagnets with the vanishing net macroscopic magnetization. The nonreciprocity of supercurrent can be realized without applying any external magnetic field or ferromagnetic exchange field, which can avoid the magnetic cross-talk between the basic elements of the devices. The high efficiency exceeding $40\%$ can be obtained and the efficiency shows the high stability when the structure parameters are changed. The diode efficiency is antisymmetric about the relative orientation angle of the superconducting leads, so that its sign can easily be inverted by adjusting the relative orientation angle. The symmetries satisfied by the current-phase difference relations and the diode efficiency are analyzed by considering the transformations of the junctions under the time-reversal, the spin-rotation and the mirror reflection operations. The high efficiency and the high stability of the Josephson diode effect in our junctions provide the possibility for the design of the field-free dissipationless diode devices.