Fleischmann Maximilian, Gupta Reena, Wullschläger Florian, Theil Simon, Weckbecker Dominik, Meded Velimir, Sharma Sangeeta, Meyer Bernd, Shallcross Samuel
Lehrstuhl für Theoretische Festkörperphysik , Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) , Staudtstraße 7-B2 , 91058 Erlangen , Germany.
Interdisciplinary Center for Molecular Materials (ICMM) and Computer-Chemistry-Center (CCC) , Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) , Nägelsbachstraße 25 , 91052 Erlangen , Germany.
Nano Lett. 2020 Feb 12;20(2):971-978. doi: 10.1021/acs.nanolett.9b04027. Epub 2020 Jan 13.
Parallel ("nested") regions of a Fermi surface (FS) drive instabilities of the electron fluid, for example, the spin density wave in elemental chromium. In one-dimensional materials, the FS is trivially fully nested (a single nesting vector connects two "Fermi dots"), while in higher dimensions only a fraction of the FS consists of parallel sheets. We demonstrate that the tiny angle regime of twist bilayer graphene (TBLG) possesses a phase, accessible by interlayer bias, in which the FS consists entirely of nestable "Fermi lines", the first example of a completely nested FS in a two-dimensional (2D) material. This nested phase is found both in the ideal as well as relaxed structure of the twist bilayer. We demonstrate excellent agreement with recent STM images of topological states in this material and elucidate the connection between these and the underlying Fermiology. We show that the geometry of the Fermi lines network is controllable by the strength of the applied interlayer bias, and thus TBLG offers unprecedented access to the physics of FS nesting in 2D materials.
费米面（FS）的平行（“嵌套”）区域会驱动电子流体的不稳定性，例如元素铬中的自旋密度波。在一维材料中，费米面平凡地完全嵌套（单个嵌套矢量连接两个“费米点”），而在更高维度中，只有一部分费米面由平行片组成。我们证明，扭曲双层石墨烯（TBLG）的微小角度区域具有一个可通过层间偏压实现的相，其中费米面完全由可嵌套的“费米线”组成，这是二维（2D）材料中完全嵌套费米面的首个例子。这种嵌套相在扭曲双层的理想结构和弛豫结构中均被发现。我们证明与该材料中拓扑态的近期扫描隧道显微镜（STM）图像具有极佳的一致性，并阐明了这些拓扑态与底层费米学之间的联系。我们表明，费米线网络的几何结构可通过所施加层间偏压的强度来控制，因此扭曲双层石墨烯为研究二维材料中费米面嵌套的物理特性提供了前所未有的途径。
