Topic : Bottom-up designed spin structures on superconducting Rashba surface alloy

Speaker : Dr. Harim Jang (Department of Physics, Universität Hamburg, Germany)

Date & Time : 2025. 07. 01, Tuesday, 11:30 ~

Place : Room No. 31317, Natural Science Building

Abstract :

 The experimental realization of topological superconductors and Majorana quasiparticles at their edges has attracted extensive interest in both directions of fundamental understanding of quantum states driven by topology and their potential applications in quantum computation. For the quasi-one-dimensional system, 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 are predicted to show a signature of Majorana modes (MM) at the chain boundaries as zero-energy states. In this talk, the electronic and magnetic properties of atomically constructed spin structures in the presence of both strong Rashba-type spin-orbit coupling and proximity-induced superconductivity will be discussed, which were probed by sub-Kelvin scanning tunneling microscopy and spectroscopy. Fe adatoms on the BiAg₂ surface alloy on Ag(111)/Nb(110) show a promising in-gap electronic structure for realizing non-trivial YSR bands when they are hybridized. By constructing Fe spin chains, we observed the edge states at both boundaries near the Fermi level and the YSR bands with minigap on the verge of our energy resolution inside the chain. These edge states show robustness in the presence of potential disorder, which is in agreement with theoretical predictions for topologically non-trivial spin chains with strong disorder. A discussion on various 3d transition metals of Co and Mn on the same surface alloy will follow for the systematic comparison.

* This work was supported by the Alexander von Humboldt Foundation.