Spins in quantum corrals coupled to superconductors

Excitations of spins on surfaces usually can be detected with the STM tip only very locally up to a few Å distance from the spin-carrying atom. When placing this magnetic atom inside a quantum corral, a cage made of many atoms that laterally confines a surface state, the excitation is projected into the eigenmodes of the quantum corral. Thereby, it can still be detected at tens of nanometers distance from the magnetic atom. Here, I will review our work on the long-range detection of excitations in magnet superconductor hybrids [1] using quantum corrals. I will first describe the proximity effects into the surface states [2] and quantum corrals [3] on thin metallic films grown on a superconducting substrate mediated by Andreev reflexions. Then, I will describe how a Yu-Shiba-Rusinov state [1] induced by a magnetic atom on such a thin film can be projected into the quantum corral eigenmodes and measured at far distances [4]. Finally, I will show our most recent work on spins in quantum corrals which confine proximitized, strongly Rashba spin orbit coupled surface states residing in bismuth-based surface alloys [5].

References
[1.] R. Lo Conte, J. Wiebe, S. Rachel, D. Morr, and R. Wiesendanger, Magnet-superconductor hybrid quantum systems: a materials platform for topological superconductivity. Riv. Nuovo Cim. (2025). https://doi.org/10.1007/s40766-024-00060-

[2.] L. Schneider, C. von Bredow, H. Kim, K. T. Ton, T. Hänke, J. Wiebe, and Roland Wiesendanger, Scanning tunneling spectroscopy study of proximity superconductivity in finite-size quantized surface states. Phys. Rev. B 110, L100505 (2024). https://doi.org/10.1103/PhysRevB.110.L100505

[3.] L. Schneider, K. That Ton, I. Ioannidis, J. Neuhaus-Steinmetz, T. Posske, R. Wiesendanger, and J. Wiebe, Proximity superconductivity in atom-by-atom crafted quantum dots. Nature 621, 60 (2023). https://doi.org/10.1038/s41586-023-06312-0

[4.] K. That Ton, C. Xu, I. Ioannidis, L. Schneider, T. Posske, R. Wiesendanger, D. K. Morr,and J. Wiebe, Non-local detection of coherent Yu-Shiba-Rusinov quantum projections. Nat. Phys. (2025). https://doi.org/10.1038/s41567-025-03109-y

[5.] H. Jang, D. Crawford, K. T. Ton, L. Schneider, J. Wiebe, M. Shimizu, H. O Jeschke, S. Rachel, R. Wiesendanger, Robustness of Majorana modes to potential disorder in Fe chains on a superconducting Rashba alloy. arXiv:2506.17414 [cond-mat.supr-con] (2025). https://doi.org/10.48550/arXiv.2506.17414