Symmetry-Broken Chern Insulators in Twisted Double Bilayer Graphene
Symmetry-Broken Chern Insulators in Twisted Double Bilayer Graphene
复制标题
扭曲双双层石墨烯中对称破缺的陈绝缘体
DOI：
10.1021/acs.nanolett.3c03414
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发表时间：
2023
期刊：
影响因子：
10.8
通讯作者：
Xu, Xiaodong
中科院分区：
文献类型：
--
作者：
He, Minhao;Cai, Jiaqi;Zhang, Ya-Hui;Liu, Yang;Li, Yuhao;Taniguchi, Takashi;Watanabe, Kenji;Cobden, David H.;Yankowitz, Matthew;Xu, Xiaodong
扭曲双层石墨烯(TDBG)由于其平坦的能带可以通过垂直位移场和扭转角连续调谐而成为研究强关联和拓扑态的丰富平台。在这里，我们构建了一个相图，表示作为这些参数的函数的相关和拓扑态，基于对包含两种不同堆栈配置的十几个tDBG器件的测量。我们发现，随着扭转角接近明显的最佳值θ≈1.34°，对称性破缺态的层次结构依次出现。在这个角度附近，我们发现了与7/2带填充相关的对称性破缺的陈绝缘态(SBCI)和与11/3填充相关的初始SBCI态。我们进一步观察到所有支持SbCi态的样品在零场下都有反常的霍尔效应，这表明在零磁场下自发的时间反转对称性破缺和可能的莫尔́晶胞放大。
Twisted double bilayer graphene (tDBG) has emerged as a rich platform for studying strongly correlated and topological states, as its flat bands can be continuously tuned by both a perpendicular displacement field and a twist angle. Here, we construct a phase diagram representing the correlated and topological states as a function of these parameters, based on measurements of over a dozen tDBG devices encompassing two distinct stacking configurations. We find a hierarchy of symmetry-broken states that emerge sequentially as the twist angle approaches an apparent optimal value of θ ≈ 1.34°. Nearby this angle, we discover a symmetry-broken Chern insulator (SBCI) state associated with a band filling of 7/2 as well as an incipient SBCI state associated with 11/3 filling. We further observe an anomalous Hall effect at zero field in all samples supporting SBCI states, indicating spontaneous time-reversal symmetry breaking and possible moiré unit cell enlargement at zero magnetic field.