Electron-electron $\left(e\text{−}e\right)$ interactions in the twisted bilayer graphene (TBG) near the magic angle ∼1.1° can lift the valley degeneracy, allowing for the realization of orbital magnetism and topological phases. However, direct measurement of the orbital-based magnetism in the TBG is still lacking up to now. Here we report evidence for orbital magnetic moment generated by the moiré-scale current loops in a TBG with a twist angle $\theta \sim 1.{68}^{\circ }$. The valley degeneracy of the 1.68° TBG is removed by $e\text{−}e$ interactions when its low-energy Van Hove singularity (VHS) is nearly half filled. A large and linear response of the valley splitting to magnetic fields is observed, which we interpret as arising from the coupling to the large orbital magnetic moment induced by chiral current loops circulating in the moiré pattern. According to our experiment, the orbital magnetic moment is about $10.7{\mu }_{\mathrm{B}}$ per moiré supercell. Our result paves the way to explore magnetism that is purely orbital in a slightly twisted graphene system.

中文翻译：

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扭曲双层石墨烯中莫尔尺度电流环产生的轨道磁矩的实验证据

电子电子 $（Ë\text{-}Ë）$扭曲的双层石墨烯（TBG）在魔角〜1.1°附近的相互作用可以解除谷的简并性，从而实现轨道磁性和拓扑相。但是，到目前为止，仍缺乏对TBG中基于轨道的磁性的直接测量。在这里，我们报告由扭转角的TBG中的莫尔尺度电流环产生的轨道磁矩的证据$\theta 〜\mathrm{1个}。{68}^{\circ }$。1.68°TBG的波谷简并被去除$Ë\text{-}Ë$低能量Van Hove奇异点（VHS）接近一半时发生交互作用。观察到了山谷分裂对磁场的大而线性的响应，我们将其解释为是由于与摩尔纹模式中循环的手性电流环所感应的大轨道磁矩的耦合而产生的。根据我们的实验，轨道磁矩约为$10.7{\mu }_{\mathrm{乙}}$每个莫尔超单元。我们的结果为探索在稍微扭曲的石墨烯系统中纯轨道磁的方法铺平了道路。