Spin-lattices coupled to proximity-superconducting Rashba-surface states

• Applicants: Professor Dr. Samir Lounis; Dr. Jens Wiebe
• Subject Area: Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 543483081

Hybrids of spin-chains coupled to proximity-superconducting electron systems with strong Rashba-type spin-orbit coupling have been theoretically suggested as platforms for the realization of topological superconductivity. The electronic states residing in Bi-based surface alloys at the (111)-surfaces of Cu and Ag are particularly appealing, as their spin-orbit couplings are several orders of magnitude larger compared to that of typical semiconductor materials. However, the experimental realization of proximity-superconductivity in such Bi-surface alloys was so far lacking. Therefore, spin-chains coupled to proximity-superconducting Bi-surface alloys are experimentally and theoretically largely unexplored. We recently realized proximity-superconductivity in the BiAg2 surface alloy of thin Ag layers grown on superconducting Nb(110) and in the Shockley surface state at the (111) surface of Cu layers grown on Nb(110). Motivated by these preliminary results we propose here a combined experimental and theoretical project for the detailed investigation of the physical phenomena in chains of transition metal atoms on proximity-superconducting BiCu2 and BiAg2 surface alloys. These atomic chains will be assembled by tip-induced manipulation and investigated using a scanning tunneling microscope. We would like to study the impact of a lateral confinement of the Rashba-surface state on the proximity-effect, on the interaction with the Shiba states of single transition metal atoms and with the Shiba bands in the chains, and whether we can detect indications of spin-triplet superconductivity with potential Majorana edge states in the hybrid system. The applicants have a well-established collaboration between experiment and theory demonstrated by a remarkable record of joint publications. It combines very strong expertise in the experimental technique of spin-polarized scanning tunneling spectroscopy at sub-Kelvin temperatures and in theoretical ab-initio calculations based on the full-potential relativistic Korringa-Kohn-Rostoker Green function method.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Philipp Rüßmann