Valley charge-transfer insulator in twisted double bilayer WSe2

LingNan Wei, Qingxin Li, Majeed Ur Rehman, Yangchen He, Dongdong An, Shiwei Li, Kenji Watanabe, Takashi Taniguchi, Martin Claassen, Kostya S. Novoselov, Dante M. Kennes, Angel Rubio, Daniel A. Rhodes (), Lede Xian (), Geliang Yu () and Lei Wang ()
Additional contact information
LingNan Wei: Nanjing University
Qingxin Li: Nanjing University
Majeed Ur Rehman: Songshan Lake Materials Laboratory
Yangchen He: University of Wisconsin
Dongdong An: Nanjing University
Shiwei Li: Nanjing University
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Martin Claassen: University of Pennsylvania
Kostya S. Novoselov: National University of Singapore
Dante M. Kennes: RWTH Aachen University and JARA-Fundamentals of Future Information Technology
Angel Rubio: Center for Free-Electron Laser Science (CFEL)
Daniel A. Rhodes: University of Wisconsin
Lede Xian: Songshan Lake Materials Laboratory
Geliang Yu: Nanjing University
Lei Wang: Nanjing University

Nature Communications, 2025, vol. 16, issue 1, 1-7

Abstract: Abstract In flat-band systems, emergent physics can be substantially modified by the presence of another nearby electronic band. For example, a Mott˘Hubbard insulator can turn into a charge transfer insulator if other electronic states enter between the upper and lower Hubbard bands. Here, we introduce twisted double bilayer (TDB) WSe2, with twist angles near 60°, as a controllable platform in which the K-valley band can be tuned to close vicinity of the Γ-valley moiré flat band. At half-filling, correlations split the Γ-valley flat band into upper and lower Hubbard bands and a charge-transfer insulator forms between the Γ-valley upper Hubbard band and K-valley band. Using gate control, we continuously move the K-valley band across the Γ-valley Hubbard bands, and observe a tunable charge-transfer insulator gap and subsequently a continuous phase transition to a metal. The tuning of Mott˘Hubbard to charge-transfer insulator establishes valley degree of freedom as a suitable knob for transitions between exotic correlated phases.

Date: 2025
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DOI: 10.1038/s41467-025-56490-w

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