Tunable correlated states and spin-polarized phases in twisted bilayer-bilayer graphene
Tunable correlated states and spin-polarized phases in twisted bilayer-bilayer graphene
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DOI：
10.1038/s41586-020-2260-6
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发表时间：
2020-07-09
期刊：
影响因子：
64.8
通讯作者：
Jarillo-Herrero, Pablo
中科院分区：
文献类型：
--
作者：
Cao, Yuan;Rodan-Legrain, Daniel;Jarillo-Herrero, Pablo
最近在魔角扭曲双层石墨烯中发现了相关绝缘体态和超导性（1，2），这使得在扭曲货车德瓦尔斯异质结构中实现的可调平带系统中的电子相关性的实验研究成为可能（3-6）。这种新颖的扭曲角自由度和控制应该是可推广到其他二维系统，这可能会表现出类似的相关物理行为，并可以使技术来调整和控制电子-电子相互作用的强度。在这里，我们报告了一个高度可调的相关系统的基础上，小角度扭曲双层双层石墨烯（TBBG），由两个旋转片的Bernal堆叠的双层石墨烯。我们发现TBBG表现出丰富的相图，具有对扭转角和电位移场的应用高度敏感的可调相关绝缘体状态，后者反映了Bernal堆叠的双层石墨烯的固有极化率（7，8）。在莫尔晶胞的所有整数电子填充处，位移场都可以使相关绝缘体态导通和截止。这些相关态对磁场的响应表明了自旋极化基态的证据，与魔角扭曲的双层石墨烯形成鲜明对比。此外，在较低的扭转角的制度，TBBG显示多组的平带附近的电荷中性，导致在许多相关的状态对应于半填充的每个这些平带，所有这些都是可调的位移场以及。我们的结果可以使探索的扭曲角和电场控制的关联相位的物质在多平带扭曲超晶格。
The recent discovery of correlated insulator states and superconductivity in magic-angle twisted bilayer graphene(1,2) has enabled the experimental investigation of electronic correlations in tunable flat-band systems realized in twisted van der Waals heterostructures(3-6). This novel twist angle degree of freedom and control should be generalizable to other two-dimensional systems, which may exhibit similar correlated physics behaviour, and could enable techniques to tune and control the strength of electron-electron interactions. Here we report a highly tunable correlated system based on small-angle twisted bilayer-bilayer graphene (TBBG), consisting of two rotated sheets of Bernal-stacked bilayer graphene. We find that TBBG exhibits a rich phase diagram, with tunable correlated insulator states that are highly sensitive to both the twist angle and the application of an electric displacement field, the latter reflecting the inherent polarizability of Bernal-stacked bilayer graphene(7,8). The correlated insulator states can be switched on and off by the displacement field at all integer electron fillings of the moire unit cell. The response of these correlated states to magnetic fields suggests evidence of spin-polarized ground states, in stark contrast to magic-angle twisted bilayer graphene. Furthermore, in the regime of lower twist angles, TBBG shows multiple sets of flat bands near charge neutrality, resulting in numerous correlated states corresponding to half-filling of each of these flat bands, all of which are tunable by the displacement field as well. Our results could enable the exploration of twist-angle- and electric-field-controlled correlated phases of matter in multi-flat-band twisted superlattices.