Topological altermagnetic Josephson junctions

Planar Josephson junctions are pivotal for engineering topological superconductivity, yet are severely hindered by the orbital effects induced by in-plane magnetic fields, or the stray fields introduced by the use of ferromagnets. Here, we propose the generic topological altermagnetic Josephson junctions (TAJJs) as a solution to this critical problem. By leveraging the anisotropic spin-polarized band splitting and zero net magnetization attributes of altermagnets, our proposed TAJJs effectively mitigate the detrimental orbital effects while hosting Majorana zero modes (MZMs) at both ends of the junction in the complete absence of external fields. Specifically, we demonstrate that MZMs emerge robustly in $${d}_{{x}^{2}-{y}^{2}}$$-wave TAJJs but vanish in the dxy-wave configuration, establishing the altermagnet orientation as an intrinsic control knob of topological superconductivity. The distinct out-of-plane spin-polarization of the MZMs provides an experimental signature for the spin-resolved measurement. Furthermore, by harnessing the synergy between the $${d}_{{x}^{2}-{y}^{2}}$$-wave altermagnet and anisotropic superconductivity, our proposal extends naturally to high-temperature superconducting platforms. Our work establishes altermagnets as a versatile paradigm for realizing MZMs, bridging conceptual innovations with scalable quantum architectures devoid of orbital effects and stray fields.