Growth, electronic structure and ultrafast electron dynamics of magnetic topological insulators

• Applicant: Professor Dr. Ulrich Höfer
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448807091

The topic of the project is the synthesis and characterization of magnetic topological insulators in which the interaction between magnetic atoms and the topological surface state (TSS) opens a gap at the Dirac node of the TSS. This effect may lead to exotic quantum phases, such as the quantum anomalous Hall (QAH) state. The primary goal of this joint proposal is the identification of the main factors that are responsible for the opening and the size of the magnetic gap at the Dirac point. In this way, we want to finally identify topological insulators (TIs) with large magnetic gap but which are truly insulating. Different classes of magnetic topological insulators will be investigated in which magnetism is induced either by doping, intrinsic magnetic compounds, or by deposition of magnetic atoms or layers. The crystals will be synthesized in Novosibirsk and characterized respect to their structural, magnetic and electrical transport properties in dependence on the composition and temperature. In Marburg, the position of the Fermi level, the size of the gap and the band structure of occupied and unoccupied states in the vicinity of the Fermi will be determined by laser ARPES and time-resolved two-photon photoemission (2PPE). The investigation of the inelastic decay dynamics of optically excited electrons in samples exhibiting the desired electronic structure will make it possible to explore the role of magnetic defect scattering and electron-phonon coupling on the ultrafast electron dynamics. It is essential to understand the interplay between the bulk and the surface states because the recovery of the equilibrium population depends on how strong they couple to each other. The observation of the decay of optically generated photocurrents directly in full two-dimensional k-space will allow us to determine the effects of microscopic momentum scattering on current transport. These experiments will be conducted above and below the magnetic ordering temperature. For selected samples we will investigate the impact of the magnetic coupling on the electron transport at the Fermi level by THz-ARPES.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Foundation for Basic Research, until 3/2022
• Co-Investigator: Privatdozent Dr. Jens Güdde
• Cooperation Partner: Professor Dr. Oleg Tereshchenko, until 3/2022