Josephson diode effect in inhomogeneous altermagnets

The Josephson diode effect (JDE) holds substantial promise for superconducting electronics. In this work, we theoretically propose a robust mechanism for achieving the JDE in s-wave superconductor/inhomogeneous altermagnets/s-wave superconductor junctions. Crucially, our proposal requires neither external magnetic fields nor spin–orbit coupling. It is demonstrated that the intrinsic inhomogeneity of altermagnets can break the time-reversal and mirror-reflection symmetries of the junction. Such symmetry breakings lead to unequal critical supercurrents in opposite directions, confirming the existence of JDE. Our calculations reveal that the JDE is significant over a broad parameter range and can be effectively tuned in various ways. Notably, the diode efficiency is antisymmetric about the spin orientation φ=π and the crystallographic orientation α=0.25π. These findings are expected to provide a feasible theoretical foundation for designing superconducting devices without magnetic fields or spin–orbit coupling.