Novel Opportunities for Exploring Atomic-Scale Magnetism in Low-dimensional Topological Quantum Materials

• Applicant: Professor Dr. Björn Trauzettel
• Subject Area: Theoretical Condensed Matter Physics ; Experimental Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546756512

This proposal aims at exploring two enticing research directions combining atomic scale magnetism and low-dimensional topological quantum materials. Based on existing preliminary results, we plan to proceed in two frontier research projects in this field which are both combinations of state-of-the-art scanning tunneling spectroscopy (STM) measurements done in Taiwan and advanced theoretical modeling based on density functional theory (DFT) undertaken in Germany for which we are requesting funding for one PhD position on each side. The first research line in our proposal is the creation of magnetic nanostructures on a self-formed Ni Kagome lattice on top of Pb(111). This brings together superconductivity, the nontrivial electronic structure of a Kagome material and magnetism on the atomic scale. In our previous results we have shown that the Ni Kagome/Pb(111) poses a superconducting surface where we were able to place Fe atoms that show Yu-Shiba-Rusinov (YSR) states when Cooper-pairs of the superconductor break apart at the magnetic adatoms. This is a fruitful combination of superconducting density functional theory calculations and low-temperature STM experiments which forms the basis for our planned activity in this filed that shows great potential in the field of topological superconductivity and Majorana zero modes (MZMs). In particular, we extend our existing work from single Fe adatoms to nanostructures of magnetic atoms made of Fe and other transition metals as well as magnetic rare-earth atoms deposited on the superconducting Ni Kagome substrate. This will allow us to study the transition from YSR to MZM states in tailored magnetic nanostructures and explore the physics of topological superconductivity and the interplay of potential non-collinear magnetic order, designed magnetic nanostructures on the atomic scale and superconductivity. The second research direction aims at single-atomic-layer honeycomb-structured materials, e.g., stanene or bismuthene, coupled to low-dimensional magnetic nanostructures. This allows combining nontrivial topological electronic structures in the two-dimensional limit with magnetic order with the potential to realize magnetic topological insulators that can show the quantum anomalous Hall effect. Recently we succeeded in covering stanene with Co nanoislands and we characterized their magnetic properties from spin-polarized (SP) STM measurements and DFT calculations. We were also able to create a honeycomb layer by depositing Mn on Bi/Ag(111) which extends this research direction to antiferromagnetic materials. Electronically, we expect interesting effects from the combination of the magnetic atoms with the honeycomb arrangement which we plan to investigate in this work. Using the SP-STM technique together with DFT-based simulations allows resolving the atomic spin structures of the honeycomb lattice on (p x radical 3)-Bi/Ag(111) and finding signatures of their topological properties.

• DFG Programme: Research Grants
• International Connection: Taiwan
• Partner Organisation: National Science and Technology Council (NSTC)
• Co-Investigators: Dr. Gustav Bihlmayer; Dr. Philipp Rüßmann
• Cooperation Partner: Professor Dr. Pin-Jui Hsu