Correlated Hofstadter spectrum and flavour phase diagram in magic-angle twisted bilayer graphene
Correlated Hofstadter spectrum and flavour phase diagram in magic-angle twisted bilayer graphene
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DOI：
10.1038/s41567-022-01589-w
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发表时间：
2021-07
期刊：
影响因子：
19.6
通讯作者：
Jiachen Yu;B. Foutty;Zhaoyu Han;M. Barber;Y. Schattner;Kenji Watanabe;T. Taniguchi;P. Phillips;Zhixuan Shen;S. Kivelson;B. Feldman
中科院分区：
文献类型：
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作者：
Jiachen Yu;B. Foutty;Zhaoyu Han;M. Barber;Y. Schattner;Kenji Watanabe;T. Taniguchi;P. Phillips;Zhixuan Shen;S. Kivelson;B. Feldman
在魔角扭曲双层石墨烯中，莫尔超晶格势产生了支持多个多体量子相的窄电子带。在存在垂直磁场的情况下，会出现进一步的丰富性，其中莫尔条纹和磁性长度尺度之间的相互作用导致分形霍夫施塔特子带。在这个强相关的 Hofstadter 平台中，多项实验已经确定了有间隙的拓扑和相关状态，但对于介入的可压缩状态中它们之间的相变知之甚少。在这里，我们同时揭示了破缺对称陈绝缘体序列，并解决了具有不同拓扑量子数和不同自旋谷风味占据的竞争态之间的急剧相变。我们的测量确定了魔角扭曲双层石墨烯中相互作用的霍夫施塔特子带的能谱，并绘制了风味占据的相图。此外，我们观察到第零朗道能级的简并性以及平交点的完全解除，表明莫尔谷分裂。我们提出了一种统一的风味极化机制，以理解拓扑、相互作用和对称性破缺作为该系统中密度和应用磁场的函数的复杂相互作用。
In magic-angle twisted bilayer graphene, the moiré superlattice potential gives rise to narrow electronic bands that support a multitude of many-body quantum phases. Further richness arises in the presence of a perpendicular magnetic field, where the interplay between moiré and magnetic length scales leads to fractal Hofstadter subbands. In this strongly correlated Hofstadter platform, multiple experiments have identified gapped topological and correlated states, but little is known about the phase transitions between them in the intervening compressible regimes. Here we simultaneously unveil sequences of broken-symmetry Chern insulators and resolve sharp phase transitions between competing states with different topological quantum numbers and different occupations of the spin-valley flavour. Our measurements determine the energy spectrum of interacting Hofstadter subbands in magic-angle twisted bilayer graphene and map out the phase diagram of flavour occupancy. In addition, we observe full lifting of the degeneracy of the zeroth Landau levels together with level crossings, indicating moiré valley splitting. We propose a unified flavour polarization mechanism to understand the intricate interplay of topology, interactions and symmetry breaking as a function of density and applied magnetic field in this system.