Interaction-driven band flattening and correlated phases in twisted bilayer graphene
Interaction-driven band flattening and correlated phases in twisted bilayer graphene
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DOI：
10.1038/s41567-021-01359-0
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发表时间：
2021-11-04
期刊：
影响因子：
19.6
通讯作者：
Nadj-Perge, Stevan
中科院分区：
文献类型：
--
作者：
Choi, Youngjoon;Kim, Hyunjin;Nadj-Perge, Stevan
平坦的电子带是“魔角”扭曲双层石墨烯的特征，具有许多相关现象（1-9）。然而，这些带的许多性质和新出现的破碎相仍然知之甚少。在这里，我们使用扫描隧道光谱检查的扭曲的双层石墨烯带和相关的带隙相的演变作为两个石墨烯层之间的扭转角的变化。我们检测填充相关的平坦化的带，这是明显的，即使当角度远高于魔角值，所以材料名义上是在一个弱相关的制度。在接近魔角时，我们进一步表明，最突出的相关间隙开始出现时，带平坦化最大化周围的某些整数填充的电子每个莫尔晶胞。我们的观察结果与一个模型是一致的，该模型表明，由能带平坦化引起的态密度的显著增强触发了级联的破环跃迁。最后，我们探讨了级联的温度依赖性，并确定了带隙的功能，开发在一个广泛的频带填充超导性的预期。我们的研究结果强调了相互作用驱动的能带平坦化在定义扭曲双层石墨烯的电子性质中的作用。
Flat electronic bands, characteristic of 'magic-angle' twisted bilayer graphene, host many correlated phenomena(1-9). Nevertheless, many properties of these bands and emerging symmetry-broken phases are still poorly understood. Here we use scanning tunnelling spectroscopy to examine the evolution of the twisted bilayer graphene bands and related gapped phases as the twist angle between the two graphene layers changes. We detect filling-dependent flattening of the bands that is appreciable even when the angle is well above the magic angle value and so the material is nominally in a weakly correlated regime. Upon approaching the magic angle, we further show that the most prominent correlated gaps begin to emerge when band flattening is maximized around certain integer fillings of electrons per moire unit cell. Our observations are consistent with a model that suggests that a significant enhancement of the density of states caused by the band flattening triggers a cascade of symmetry-breaking transitions. Finally, we explore the temperature dependence of the cascade and identify gapped features that develop in a broad range of band fillings where superconductivity is expected. Our results highlight the role of interaction-driven band flattening in defining the electronic properties of twisted bilayer graphene.