Shi Qianhui, Shih En-Min, Gustafsson Martin V, Rhodes Daniel A, Kim Bumho, Watanabe Kenji, Taniguchi Takashi, Papić Zlatko, Hone James, Dean Cory R
Department of Physics, Columbia University, New York, NY, USA.
Raytheon BBN Technologies, Cambridge, MA, USA.
Nat Nanotechnol. 2020 Jul;15(7):569-573. doi: 10.1038/s41565-020-0685-6. Epub 2020 Jul 6.
Monolayer semiconducting transition-metal dichalcogenides (TMDs) represent a unique class of two-dimensional (2D) electron systems. Their atomically thin structure facilitates gate tunability just like graphene does, but unlike graphene, TMDs have the advantage of a sizable band gap and strong spin-orbit coupling. Measurements under large magnetic fields have revealed an unusual Landau level (LL) structure, distinct from other 2D electron systems. However, owing to the limited sample quality and poor electrical contact, probing the lowest LLs has been challenging, and observation of electron correlations within the fractionally filled LL regime has not been possible. Here, through bulk electronic compressibility measurements, we investigate the LL structure of monolayer WSe in the extreme quantum limit, and observe fractional quantum Hall states in the lowest three LLs. The odd-denominator fractional quantum Hall sequences demonstrate a systematic evolution with the LL orbital index, consistent with generic theoretical expectations. In addition, we observe an even-denominator state in the second LL that is expected to host non-Abelian statistics. Our results suggest that the 2D semiconductors can provide an experimental platform that closely resembles idealized theoretical models in the quantum Hall regime.
单层半导体过渡金属二硫属化物（TMDs）代表了一类独特的二维（2D）电子系统。它们原子级别的薄结构使得其具有与石墨烯类似的栅极可调性，但与石墨烯不同的是，TMDs具有可观的带隙和强自旋轨道耦合的优势。在强磁场下的测量揭示了一种不同于其他二维电子系统的异常朗道能级（LL）结构。然而，由于样品质量有限和电接触不良，探测最低朗道能级一直具有挑战性，并且在部分填充朗道能级区域内观察电子关联也一直无法实现。在这里，通过体电子压缩性测量，我们研究了单层WSe在极端量子极限下的朗道能级结构，并在最低的三个朗道能级中观察到了分数量子霍尔态。奇数分母的分数量子霍尔序列显示出随着朗道能级轨道指数的系统演化，这与一般的理论预期一致。此外，我们在第二个朗道能级中观察到了一个预期具有非阿贝尔统计特性的偶数分母态。我们的结果表明，二维半导体可以提供一个在量子霍尔区域与理想化理论模型非常相似的实验平台。
