[论文解读] Visualization of the flat electronic band in twisted bilayer graphene near the magic angle twist

M. Iqbal Bakti Utama, Roland J. Koch+16 more|arXiv (Cornell University)|Dec 2, 2019

Graphene research and applications参考文献 44被引用 45

一句话总结

该论文通过 nanoARPES 在扭曲双层石墨烯接近临界角处直接可视化平坦莫尔子带，显示在室温下接近电荷中性点的平坦色散。

ABSTRACT

Bilayer graphene was theorized to host a moire miniband with flat dispersion if the layers are stacked at specific twist angles known as the magic angles. Recently, such twisted bilayer graphene (tBLG) with the first magic angle twist was reported to exhibit correlated insulating state and superconductivity, where the presence of the flat miniband in the system is thought to be essential for the emergence of these ordered phases in the transport measurements. Tunneling spectroscopy and electronic compressibility measurements in tBLG have revealed a van Hove singularity that is consistent with the presence of the flat miniband. However, a direct observation of the flat dispersion in the momentum-space of such moire miniband in tBLG is still elusive. Here, we report the visualization of the flat moire miniband by using angle-resolved photoemission spectroscopy with nanoscale resolution (nanoARPES). The high spatial resolution in nanoARPES enabled the measurement of the local electronic structure of the tBLG. We clearly demonstrate the existence of the flat moire band near the charge neutrality for tBLG close to the magic angle at room temperature.

研究动机与目标

• 推动理解扭曲双层石墨烯中平坦莫尔子带是相关绝缘和超导相的关键因素。
• 提供对近临界角的平坦带在动量空间中的直接观测，利用纳米尺度空间分辨率。
• 展示 nanoARPES 能在室温下探测扭曲双层石墨烯的局部电子结构的能力。

提出的方法

• 使用带有纳米尺度分辨率的角分辨光电子能谱（nanoARPES）以测量局部电子结构。
• 绘制接近临界角的扭曲双层石墨烯的动量分辨电子色散。
• 识别并可视化接近电荷中性点的平坦莫尔子带。
• 利用高空间分辨率访问莫尔图案的局部变化。

实验结果

研究问题

• RQ1 在动量空间中能否直接可视化接近临界角的扭曲双层石墨烯中的平坦莫尔子带？
• RQ2 是否可以使用 nanoARPES 在室温下观测到平坦色散？
• RQ3 nanoARPES 是否揭示与接近电荷中性点的莫尔子带相关的局部电子结构？

主要发现

• NanoARPES 使在接近临界角的扭曲双层石墨烯中平坦莫尔子带的可视化成为可能。
• 平带观察到靠近电荷中性点。
• 在室温下观测到平坦色散，证明子带特征的鲁棒性。
• 高空间分辨率使在 tBLG 中测量局部电子结构成为可能。