Zhang Song-Bo, Hu Lun-Hui, Neupert Titus
Hefei National Laboratory, Hefei, Anhui, 230088, China.
International Center for Quantum Design of Functional Materials (ICQD), University of Science and Technology of China, Hefei, Anhui, 230026, China.
Nat Commun. 2024 Feb 27;15(1):1801. doi: 10.1038/s41467-024-45951-3.
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 RuO and KRuO.
有限动量库珀对是一种非常规超导形式，人们普遍认为它需要有限磁化强度。交替磁性是一种新兴磁相，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。在此，我们研究连接到传统s波超导体的金属交替磁体中的库珀对。值得注意的是，我们发现尽管系统净磁化强度为零，但在交替磁体中诱导出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，并呈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) 序参量中高度依赖取向的振荡，(ii) 约瑟夫森超电流中可控的0-π转变，(iii) 与自旋分裂消失方向平行的结中存在大斜角库珀对转移轨迹，以及(iv) 沿不同方向取向的结中呈现出不同的夫琅禾费图样。最后，我们讨论了在诸如RuO和KRuO等候选材料中实现我们预测的情况。
