Regensburg 2025 – scientific programme

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O: Fachverband Oberflächenphysik

O 59: Spins on Surfaces at the Atomic Scale I

O 59.8: Talk

Wednesday, March 19, 2025, 12:15–12:30, H6

Edge states in bottom-up designed spin chains on a superconducting Rashba surface alloy — •Harim Jang, Khai That Ton, Lucas Schneider, Jens Wiebe, and Roland Wiesendanger — Department of Physics, University of Hamburg, Hamburg, Germany

The experimental quest for topological superconductors and emergent Majorana modes (MMs) at their edges have attracted significant interest recently in both directions of fundamental understanding of topology-driven quantum states and their potential applications in quantum computation leveraging the robustness by topological protection. A spin chain on a conventional superconductor in the presence of spin-orbit coupling is one of the promising platforms for realizing topologically non-trivial Yu-Shiba-Rusinov (YSR) bands, which can show signatures of MMs at the chain boundaries in the form of zero-energy states [1]. In this talk, we report on bottom-up designed Fe chains on the Rashba surface-alloy BiAg2 grown on Ag(111)/Nb(110) and the detailed investigation of prominent states near the Fermi level at both chain ends, which are studied using scanning tunneling spectroscopy at sub-Kelvin temperatures. The atomically constructed Fe chains on the BiAg2 alloy with proximity-induced superconductivity originating from the bulk Nb substrate show YSR bands with minigaps on the verge of our energy resolution inside the chain and edge states near the Fermi level at the chain’s ends. The results are systematically compared to chains composed of other 3d transition metals, Mn and Co, on the same surface, revealing the absence of edge states for both cases. [1] S. Rachel and R. Wiesendanger, Phys. Rep. 1099, 1 (2025)

Keywords: Majorana zero mode; Topological superconductivity; Spin-orbit coupling; Scanning tunneling spectroscopy