Field-free Josephson diode effect in an Ising-superconductor/altermagnet/Ising-superconductor Josephson junction

Abstract

Altermagnets (AMs) are an exotic class of antiferromagnet that exhibit spin splitting even in the absence of net global magnetization and spin-orbit coupling (SOC) effects. In this work, we investigated theoretically the supercurrent nonreciprocity in an Ising-superconductor (ISC)/altermagnet/Ising-superconductor Josephson junction which revealed asymmetric Josephson critical currents, 0−π transitions, and an anomalous current-phase relation. A strong Josephson diode efficiency (JDE) is observed due to the combined effects of AM strength and orientations in a conventional superconductor even in absence of SOC. However, it significantly enhances in presence of intrinsic SOC (ISOC), resulting in pronounced diode effect in both the single- and double-band ISC/AM based Josephson junction. Additionally, it is observed that JDE is more prominent at higher AM strengths with intermediate orientations in all scenarios. Notably, it is significantly suppressed for orientations 0∘ and 45∘. Our results also indicate that barrier transparency and AM lengths play a crucial role in optimizing the JDE. In a single-band ISC/AM system JDE persists for any AM length, while it reduces at longer AM junctions in case of a double-band ISC/AM system. Moreover, our results suggest that a diode efficiency of ≈52% can be achieved in the proposed Josephson junction in both the single- and double-band ISC/AM Josephson junction by considering strong AM strength. Furthermore, the single-band ISC offers a wide AM orientation range in contrast to the double-band ISC for better tunability and optimization of JDE. Our findings highlight the impact of AM strength, orientation, and ISOC on the JDE efficiency, offering insights for superconducting diode design.

Source-reported materials — not catalogue approval

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