Finite-momentum Cooper pairing is an unconventional form of superconductivity that is widely believed to require finite magnetization. Altermagnetism is an emerging magnetic phase with highly anisotropic spin-splitting of specific symmetries, but zero net magnetization. Here, we study Cooper pairing in metallic altermagnets connected to conventional s-wave superconductors. Remarkably, we find that the Cooper pairs induced in the altermagnets acquire a finite center-of-mass momentum, despite the zero net magnetization in the system. This anomalous Cooper-pair momentum strongly depends on the propagation direction and exhibits unusual symmetric patterns. Furthermore, it yields several unique features: (i) highly orientation-dependent oscillations in the order parameter, (ii) controllable 0-π transitions in the Josephson supercurrent, (iii) large-oblique-angle Cooper-pair transfer trajectories in junctions parallel with the direction where spin splitting vanishes, and (iv) distinct Fraunhofer patterns in junctions oriented along different directions. Finally, we discuss the implementation of our predictions in candidate materials such as RuO₂ and KRu₄O₈.

有限动量库珀配对是超导的一种非常规形式，人们普遍认为它需要有限的磁化强度。交变磁性是一种新兴的磁相，具有特定对称性的高度各向异性自旋分裂，但净磁化强度为零。在这里，我们研究了与传统s波超导体连接的金属交替磁体中的库珀配对。值得注意的是，我们发现尽管系统中的净磁化强度为零，但交流磁体中感应的库珀对获得了有限的质心动量。这种反常的库珀对动量强烈依赖于传播方向，并表现出不寻常的对称模式。此外，它还产生了几个独特的特征：（i）阶次参数中高度依赖方向的振荡，（ii）约瑟夫森超流中的可控0- π跃迁，（iii）结点平行的大斜角库珀对转移轨迹自旋分裂消失的方向，以及（iv）沿不同方向的结点中不同的夫琅和费模式。最后，我们讨论了我们的预测在 RuO ₂和 KRu ₄ O ₈等候选材料中的实现。