de Jong Tobias A, Benschop Tjerk, Chen Xingchen, Krasovskii Eugene E, de Dood Michiel J A, Tromp Rudolf M, Allan Milan P, van der Molen Sense Jan
Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA, Leiden, The Netherlands.
Departamento de Polímeros y Materiales Avanzados: Física, Química y Tecnología, Universidad del Pais Vasco UPV/EHU, 20080, San Sebastián/Donostia, Spain.
Nat Commun. 2022 Jan 10;13(1):70. doi: 10.1038/s41467-021-27646-1.
In 'magic angle' twisted bilayer graphene (TBG) a flat band forms, yielding correlated insulator behavior and superconductivity. In general, the moiré structure in TBG varies spatially, influencing the overall conductance properties of devices. Hence, to understand the wide variety of phase diagrams observed, a detailed understanding of local variations is needed. Here, we study spatial and temporal variations of the moiré pattern in TBG using aberration-corrected Low Energy Electron Microscopy (AC-LEEM). We find a smaller spatial variation than reported previously. Furthermore, we observe thermal fluctuations corresponding to collective atomic displacements over 70 pm on a timescale of seconds. Remarkably, no untwisting is found up to 600 C. We conclude that thermal annealing can be used to decrease local disorder. Finally, we observe edge dislocations in the underlying atomic lattice, the moiré structure acting as a magnifying glass. These topological defects are anticipated to exhibit unique local electronic properties.
在“魔角”扭曲双层石墨烯（TBG）中会形成一个平带，产生关联绝缘行为和超导性。一般来说，TBG中的莫尔结构在空间上会发生变化，从而影响器件的整体电导特性。因此，为了理解所观察到的各种各样的相图，需要对局部变化有详细的了解。在这里，我们使用像差校正低能电子显微镜（AC-LEEM）研究了TBG中莫尔图案的空间和时间变化。我们发现其空间变化比之前报道的要小。此外，我们观察到在数秒的时间尺度上，对应于超过70皮米的集体原子位移的热涨落。值得注意的是，在高达600℃的温度下未发现解扭现象。我们得出结论，热退火可用于减少局部无序。最后，我们在底层原子晶格中观察到边缘位错，莫尔结构起到了放大镜的作用。预计这些拓扑缺陷会表现出独特的局部电子特性。
