Kim Kyounghwan, DaSilva Ashley, Huang Shengqiang, Fallahazad Babak, Larentis Stefano, Taniguchi Takashi, Watanabe Kenji, LeRoy Brian J, MacDonald Allan H, Tutuc Emanuel
Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78758.
Department of Physics, The University of Texas at Austin, Austin, TX 78712.
Proc Natl Acad Sci U S A. 2017 Mar 28;114(13):3364-3369. doi: 10.1073/pnas.1620140114. Epub 2017 Mar 14.
According to electronic structure theory, bilayer graphene is expected to have anomalous electronic properties when it has long-period moiré patterns produced by small misalignments between its individual layer honeycomb lattices. We have realized bilayer graphene moiré crystals with accurately controlled twist angles smaller than 1° and studied their properties using scanning probe microscopy and electron transport. We observe conductivity minima at charge neutrality, satellite gaps that appear at anomalous carrier densities for twist angles smaller than 1°, and tunneling densities-of-states that are strongly dependent on carrier density. These features are robust up to large transverse electric fields. In perpendicular magnetic fields, we observe the emergence of a Hofstadter butterfly in the energy spectrum, with fourfold degenerate Landau levels, and broken symmetry quantum Hall states at filling factors ±1, 2, 3. These observations demonstrate that at small twist angles, the electronic properties of bilayer graphene moiré crystals are strongly altered by electron-electron interactions.
根据电子结构理论，当双层石墨烯通过其各层蜂窝晶格之间的微小错位产生长周期莫尔条纹图案时，预计会具有异常的电子特性。我们已经实现了扭转角精确控制在小于1°的双层石墨烯莫尔晶体，并使用扫描探针显微镜和电子输运对其性质进行了研究。我们观察到在电荷中性时的电导率最小值、对于小于1°的扭转角在异常载流子密度下出现的卫星能隙以及强烈依赖于载流子密度的隧穿态密度。这些特征在大的横向电场下仍然稳健。在垂直磁场中，我们观察到能谱中出现了霍夫施塔特蝴蝶，具有四重简并的朗道能级，以及在填充因子±1、2、3时的对称性破缺量子霍尔态。这些观察结果表明，在小扭转角下，双层石墨烯莫尔晶体的电子性质会被电子 - 电子相互作用强烈改变。
