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

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