Moiré Superlattice Effects and Band Structure Evolution in Near-30-Degree Twisted Bilayer Graphene,ACS Nano

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Moiré Superlattice Effects and Band Structure Evolution in Near-30-Degree Twisted Bilayer Graphene
ACS Nano ( IF 15.8 ) Pub Date : 2022-01-24 , DOI: 10.1021/acsnano.1c06439
Matthew J Hamer _{1,

2} , Alessio Giampietri ₃ , Viktor Kandyba ₃ , Francesca Genuzio ₃ , Tevfik O Menteş ₃ , Andrea Locatelli ₃ , Roman V Gorbachev _{1,

2,

4} , Alexei Barinov ₃ , Marcin Mucha-Kruczyński _{5,

6}

Affiliation

In stacks of two-dimensional crystals, mismatch of their lattice constants and misalignment of crystallographic axes lead to formation of moiré patterns. We show that moiré superlattice effects persist in twisted bilayer graphene (tBLG) with large twists and short moiré periods. Using angle-resolved photoemission, we observe dramatic changes in valence band topology across large regions of the Brillouin zone, including the vicinity of the saddle point at M and across 3 eV from the Dirac points. In this energy range, we resolve several moiré minibands and detect signatures of secondary Dirac points in the reconstructed dispersions. For twists θ > 21.8°, the low-energy minigaps are not due to cone anticrossing as is the case at smaller twist angles but rather due to moiré scattering of electrons in one graphene layer on the potential of the other which generates intervalley coupling. Our work demonstrates the robustness of the mechanisms which enable engineering of electronic dispersions of stacks of two-dimensional crystals by tuning the interface twist angles. It also shows that large-angle tBLG hosts electronic minigaps and van Hove singularities of different origin which, given recent progress in extreme doping of graphene, could be explored experimentally.

中文翻译：

近30度扭曲双层石墨烯中的莫尔超晶格效应和能带结构演化

在二维晶体的堆叠中，它们的晶格常数的不匹配和晶轴的未对准导致形成莫尔图案。我们表明莫尔超晶格效应在扭曲的双层石墨烯（tBLG）中持续存在，具有大的扭曲和短的莫尔周期。使用角度分辨光电发射，我们观察到布里渊区大区域的价带拓扑结构发生了巨大变化，包括M处的鞍点附近距离狄拉克点 3 eV。在这个能量范围内，我们解析了几个莫尔微带并检测了重建色散中次级狄拉克点的特征。对于扭曲 θ > 21.8°，低能小间隙不是由于锥体反交叉（如较小扭曲角的情况），而是由于一个石墨烯层中电子的莫尔散射在另一个石墨烯层的电位上产生间隔耦合。我们的工作证明了通过调整界面扭曲角来设计二维晶体堆叠电子色散的机制的稳健性。它还表明，大角 tBLG 拥有不同来源的电子小间隙和范霍夫奇点，鉴于最近在石墨烯的极端掺杂方面取得的进展，可以通过实验进行探索。

更新日期：2022-01-24

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