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)，即强磁场中的2D电子进行实验研究和理论理解。更具体地说，我们计划使用自旋分辨扫描隧道显微镜来研究石墨烯中的Skrymion，其中由于双谷简并而产生的额外的“伪自旋”与电子的物理自旋相结合。因此，石墨烯提供了一种独特的可能性来研究既适合自旋又适合山谷的Skyrmions，并允许产生更奇异的纹理，被称为SU(4)Skyrmions。最早的理论研究表明，它们在电子亚晶格占据中产生了清晰的指纹，这是光谱可及的。实际上，我们所关注的第零个朗道能级中的电子具有与亚晶格重合的谷伪自旋的特征--伪自旋天子因此等价于亚晶格占据中的织构。对于SU(4)Skyrmions的光谱鉴定，需要对无序效应和钉扎机制进行详细的分析。这一点，以及围绕天空微子的自旋激发的理论研究和实验探测，是该项目的核心部分。在更具前瞻性的水平上，我们计划研究这些天子和自旋谷织构在样品边缘和栅定义的界面上的命运。实验将在德国RWTH亚琛大学进行，而法国奥赛大学的法国CNRS部分则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.