High-Field Skyrmions in Graphene

该项目旨在对量子霍尔系统中的skyrmions（拓扑自旋纹理）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skrymion，其中由于双重谷简并而产生的额外“赝自旋”与电子的物理自旋相结合。因此，石墨烯提供了研究自旋和谷的独特可能性，并允许更奇特的纹理，创造了SU（4）skyrmions。第一个理论研究表明，它们在电子子晶格占据中产生了清晰的指纹，这是光谱学上可以达到的。事实上，我们关注的第零朗道能级上的电子的特征是与子晶格一致的谷赝自旋--因此赝自旋skyrmion等价于子晶格占据中的纹理。对于SU（4）skyrmions的光谱识别，需要对无序效应和钉扎机制进行详细的分析。这一点，沿着理论研究和实验探测的自旋激发周围的skyrmions是该项目的核心部分。在一个更前瞻性的水平上，我们计划研究这些skyrmions和自旋谷纹理的样品边缘和门定义的接口的命运。实验将在德国亚琛工业大学进行，而法国国家科学研究中心位于奥赛LPS的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.