Rickhaus Peter, Liu Ming-Hao, Kurpas Marcin, Kurzmann Annika, Lee Yongjin, Overweg Hiske, Eich Marius, Pisoni Riccardo, Taniguchi Takashi, Watanabe Kenji, Richter Klaus, Ensslin Klaus, Ihn Thomas
Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland.
Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan.
Sci Adv. 2020 Mar 13;6(11):eaay8409. doi: 10.1126/sciadv.aay8409. eCollection 2020 Mar.
When two dimensional crystals are atomically close, their finite thickness becomes relevant. Using transport measurements, we investigate the electrostatics of two graphene layers, twisted by θ = 22° such that the layers are decoupled by the huge momentum mismatch between the K and K' points of the two layers. We observe a splitting of the zero-density lines of the two layers with increasing interlayer energy difference. This splitting is given by the ratio of single-layer quantum capacitance over interlayer capacitance and is therefore suited to extract . We explain the large observed value of by considering the finite dielectric thickness of each graphene layer and determine ≈ 2.6 Å. In a second experiment, we map out the entire density range with a Fabry-Pérot resonator. We can precisely measure the Fermi wavelength λ in each layer, showing that the layers are decoupled. Our findings are reproduced using tight-binding calculations.
当二维晶体在原子尺度上接近时，其有限的厚度就变得至关重要。通过输运测量，我们研究了两层石墨烯的静电学性质，这两层石墨烯以θ = 22°扭转，使得两层通过两层K点和K'点之间巨大的动量失配而解耦。我们观察到随着层间能量差的增加，两层的零密度线出现分裂。这种分裂由单层量子电容与层间电容的比值给出，因此适合用于提取。通过考虑每个石墨烯层有限的介电厚度，我们解释了所观察到的的较大值，并确定≈2.6 Å。在第二个实验中，我们使用法布里 - 珀罗谐振器绘制出整个密度范围。我们能够精确测量每层中的费米波长λ，表明两层是解耦的。我们的发现通过紧束缚计算得以重现。
