Mott and generalized Wigner crystal states in WSe2/WS2 moiré superlattices

• Published in: Nature (London) Vol. 579; no. 7799; pp. 359 - 363
• Main Authors: Regan, Emma C., Wang, Danqing, Jin, Chenhao, Bakti Utama, M. Iqbal, Gao, Beini, Wei, Xin, Zhao, Sihan, Zhao, Wenyu, Zhang, Zuocheng, Yumigeta, Kentaro, Blei, Mark, Carlström, Johan D., Watanabe, Kenji, Taniguchi, Takashi, Tongay, Sefaattin, Crommie, Michael, Zettl, Alex, Wang, Feng
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 19.03.2020
• Subjects: Boron; Boron nitride; Chalcogenides; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Correlation analysis; Crystallization; Electron states; Graphene; Graphite; Heterostructures; MATERIALS SCIENCE; Quantum fluids and solids; Spectrum allocation; Spin-orbit interactions; Superlattices; Transition metal compounds; Two-dimensional materials
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-020-2092-4

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 twistedbilayer graphene and ABC trilayer graphene/boron nitride moiré superlattices1-4. Transition metal dichalcogenide moiré heterostructures provide another model system for the study of correlated quantum phenomena5 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 WSe2/WS2 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 ofthe superlattice, which we assign to generalized Wigner crystallization on the underlying lattice6-11. Furthermore, the spin-valley optical selection rules12-14 of transition metal dichalcogenide heterostructures allow us to optically create and investigate lowenergy 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.