High-Field Skyrmions in Graphene

• Applicant: Professor Dr. Markus Morgenstern
• Subject Area: Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391044850

The project aims at an experimental investigation and a theoretical understanding of skyrmions (topological spin textures) in quantum-Hall systems, i.e., 2D electrons in a strong magnetic field. More specifically, using spin-resolved scanning tunneling microscopy, we plan to study skrymions in graphene, where an additional "pseudospin" due to the twofold valley degeneracy combines with the physical spin of the electrons. Graphene, thus, offers the unique possibility to investigate skyrmions that appeal to both, spin and valley, and allows for more exotic textures, coined SU(4) skyrmions. First theoretical studies indicate that they yield a clear fingerprint in the electronic sublattice occupation, which is spectroscopically accessible.Indeed, electrons in the zeroth Landau level, that we concentrate on, are characterized by a valley pseudospin that coincides with the sublattice -- a pseudospin skyrmion is thus equivalent to a texture in sublattice occupation. For a spectroscopic identification of SU(4) skyrmions, one requires a detailed analysis of disorder effects and pinning mechanisms. This, along with a theoretical study and an experimental probe of spin excitations around the skyrmions is a central part of the project. On a more prospective level, we plan to study the fate of these skyrmions and spin-valley textures at the sample edges and gate-defined interfaces. Experiments will be taken out at RWTH Aachen University, Germany, while the French CNRS component at LPS, Orsay, provides necessary theoretical studies.

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partner: Professor Dr. Mark Oliver Goerbig