Department of Physics, University of California at Berkeley, Berkeley, CA, USA.
Graduate Group in Applied Science and Technology, University of California at Berkeley, Berkeley, CA, USA.
Nature. 2020 Mar;579(7799):359-363. doi: 10.1038/s41586-020-2092-4. Epub 2020 Mar 18.
Moiré superlattices can be used to engineer strongly correlated electronic states in two-dimensional van der Waals heterostructures, as recently demonstrated in the correlated insulating and superconducting states observed in magic-angle twisted-bilayer graphene and ABC trilayer graphene/boron nitride moiré superlattices. Transition metal dichalcogenide moiré heterostructures provide another model system for the study of correlated quantum phenomena because of their strong light-matter interactions and large spin-orbit coupling. However, experimental observation of correlated insulating states in this system is challenging with traditional transport techniques. Here we report the optical detection of strongly correlated phases in semiconducting WSe/WS moiré superlattices. We use a sensitive optical detection technique and reveal a Mott insulator state at one hole per superlattice site and surprising insulating phases at 1/3 and 2/3 filling of the superlattice, which we assign to generalized Wigner crystallization on the underlying lattice. Furthermore, the spin-valley optical selection rules of transition metal dichalcogenide heterostructures allow us to optically create and investigate low-energy excited spin states in the Mott insulator. We measure a very long spin relaxation lifetime of many microseconds in the Mott insulating state, orders of magnitude longer than that of charge excitations. Our studies highlight the value of using moiré superlattices beyond graphene to explore correlated physics.
Moiré 超晶格可用于工程二维范德瓦尔斯异质结构中的强关联电子态，最近在转角双层石墨烯和 ABC 三层石墨烯/氮化硼莫尔超晶格中观察到的关联绝缘和超导态中得到了证明。过渡金属二卤化物莫尔超晶格因其强的光物质相互作用和大的自旋轨道耦合，是研究关联量子现象的另一个模型系统。然而，用传统的输运技术在这个系统中观察到关联绝缘态是具有挑战性的。在这里，我们报告了在半导体 WSe/WS 莫尔超晶格中强关联相的光学检测。我们使用了一种灵敏的光学检测技术，在每个超晶格位置有一个空穴时，我们揭示了一个莫特绝缘态，而在超晶格的 1/3 和 2/3 填充时，我们发现了令人惊讶的绝缘相，我们将其归因于底层晶格上的广义维格纳结晶。此外，过渡金属二卤化物异质结构的自旋-谷光学选择定则允许我们在莫特绝缘体内光学地创建和研究低能激发的自旋态。我们在莫特绝缘态中测量到了非常长的自旋弛豫寿命，长达数微秒，比电荷激发的寿命长几个数量级。我们的研究强调了使用莫尔超晶格超越石墨烯来探索关联物理的价值。
