Magnetic topological insulators probed by scanning tunneling spectroscopy

• Applicant: Professor Dr. Markus Morgenstern
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539545304

The quantum anomalous Hall effect could replace or, at least, complement the quantum Hall effect in metrology due to its advantageous absence of external magnetic fields. It is, moreover, a promising platform to realize Majorana zero modes via superconducting proximity without ex¬ternal magnetic fields. A central challenge is to improve the thermal stability related to the ho¬mogeneity of the materials. In this project, we will probe the sources of such inhomogeneity by scanning tunnelling microscopy using the stoichiometric magnetic topological insulators Mn(Sb,Bi)2Te4 and related compounds with a focus on the recently discovered ferromagnetic TI Mn1.06Sb1.94Te4. We will map sizes and centre positions of the magneti¬cally induced gap within the topological surface state as related to magnetic disorder and elec¬trostatic disorder, respec¬tively. We will explore the tuning of the gap with external magnetic fields as well as the spatio¬temporal fluctuations of the gap at elevated temperatures. We will also map the resulting edge states, in particular of exfoliated material including the possibility of gating. Eventually, we will deposit superconductors on the magnetic topological insulator probing the proximity gap that partially should host zero bias peaks at the interface. A continuous feedback with our partners for improvement of the materials grown by molecular beam epitaxy aims at materials and inter¬faces operating at temperatures up to the critical temperatures of the materials. The central aim of the project, is a comprehensive understanding of the role of different types of disor¬der on the stability of magnetic gaps, edge states and eventually Majorana zero modes.

• DFG Programme: Research Grants
• International Connection: Austria, Netherlands, Switzerland
• Major Instrumentation: Trockener Magnet für existierenden UHV-Closed-Cycle-Kryostat (3T)
• Instrumentation Group: 0120 Supraleitende Labormagnete
• Cooperation Partners: Professorin Dr. Anna Isaeva; Professor Dr. Daniel Loss; Professor Dr. Gunther Springholz