Probing the topologically trivial nature of end states in antiferromagnetic atomic chains on superconductors

• Published in: Nature communications Vol. 14; no. 1; p. 2742
• Main Authors: Schneider, Lucas, Beck, Philip, Rózsa, Levente, Posske, Thore, Wiebe, Jens, Wiesendanger, Roland
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 12.05.2023; Nature Publishing Group; Nature Portfolio
• Subjects: 147/138; 639/766/119/1003; 639/766/119/2792/4129; 639/766/119/997; Antiferromagnetism; Defects; Electrons; Energy; Humanities and Social Sciences; multidisciplinary; Physics; Science; Science (multidisciplinary); Solid state physics; Spectroscopy; Spectrum analysis; Spin-orbit interactions; Superconductors; Theoretical physics; Topography; Topology
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-38369-w

Spin chains proximitized by s -wave superconductors are predicted to enter a mini-gapped phase with topologically protected Majorana modes (MMs) localized at their ends. However, the presence of non-topological end states mimicking MM properties can hinder their unambiguous observation. Here, we report on a direct method to exclude the non-local nature of end states via scanning tunneling spectroscopy by introducing a locally perturbing defect on one of the chain’s ends. We apply this method to particular end states observed in antiferromagnetic spin chains within a large minigap, thereby proving their topologically trivial character. A minimal model shows that, while wide trivial minigaps hosting end states are easily achieved in antiferromagnetic spin chains, unrealistically large spin-orbit coupling is required to drive the system into a topologically gapped phase with MMs. The methodology of perturbing candidate topological edge modes in future experiments is a powerful tool to probe their stability against local disorder. Spin chains on superconductors have been studied as a possible venue for zero-energy Majorana bound states at the ends of the chain. Here, the authors observe localized end states in antiferromagnetic chains, but rule out a Majorana origin of these states by perturbing them with local defects.