Hoke Jesse C, Li Yifan, May-Mann Julian, Watanabe Kenji, Taniguchi Takashi, Bradlyn Barry, Hughes Taylor L, Feldman Benjamin E
Department of Physics, Stanford University, Stanford, CA, 94305, USA.
Geballe Laboratory for Advanced Materials, Stanford, CA, 94305, USA.
Nat Commun. 2024 May 21;15(1):4321. doi: 10.1038/s41467-024-48385-z.
The flat bands in magic-angle twisted bilayer graphene (MATBG) provide an especially rich arena to investigate interaction-driven ground states. While progress has been made in identifying the correlated insulators and their excitations at commensurate moiré filling factors, the spin-valley polarizations of the topological states that emerge at high magnetic field remain unknown. Here we introduce a technique based on twist-decoupled van der Waals layers that enables measurement of their electronic band structure and-by studying the backscattering between counter-propagating edge states-the determination of the relative spin polarization of their edge modes. We find that the symmetry-broken quantum Hall states that extend from the charge neutrality point in MATBG are spin unpolarized at even integer filling factors. The measurements also indicate that the correlated Chern insulator emerging from half filling of the flat valence band is spin unpolarized and suggest that its conduction band counterpart may be spin polarized.
魔角扭曲双层石墨烯（MATBG）中的平带为研究相互作用驱动的基态提供了一个特别丰富的领域。虽然在确定具有相称莫尔填充因子的相关绝缘体及其激发方面已经取得了进展，但在高磁场下出现的拓扑态的自旋谷极化仍然未知。在这里，我们介绍了一种基于扭曲解耦范德华层的技术，该技术能够测量其电子能带结构，并通过研究反向传播边缘态之间的背散射来确定其边缘模式的相对自旋极化。我们发现，从MATBG中的电荷中性点延伸出的对称性破缺量子霍尔态在偶数整数填充因子下是自旋非极化的。测量还表明，从平带价带半填充中出现的相关陈绝缘体是自旋非极化的，并表明其导带对应物可能是自旋极化的。
