High-Field Skyrmions in Graphene

该项目旨在对量子霍尔系统中的skyrmions（拓扑自旋织构）进行实验研究和理论理解，即强磁场中的二维电子。更具体地说，使用自旋分辨扫描隧道显微镜，我们计划研究石墨烯中的skrymions，其中由于双谷简并而产生的额外“伪自旋”与电子的物理自旋相结合。因此，石墨烯提供了独特的可能性来研究同时吸引自旋和谷的skyrmions，并允许更多奇特的纹理，称为SU(4) skyrmions。首先，理论研究表明，它们在电子亚晶格占位中产生了清晰的指纹，这是光谱可访问的。事实上，我们所关注的第0朗道能级上的电子，其特征是与亚晶格重合的谷伪自旋——因此，伪自旋skyrmion相当于亚晶格占据中的纹理。对于SU(4) skyrmions的光谱鉴定，需要对无序效应和固定机制进行详细的分析。这一点，以及对摩天大楼周围自旋激发的理论研究和实验探测，是该项目的核心部分。在更有前景的层面上，我们计划研究这些skyrmions和自旋谷纹理在样品边缘和门定义界面的命运。实验将在德国亚琛工业大学进行，而位于奥赛LPS的法国CNRS部分将提供必要的理论研究。

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.