Excitonic insulator in semiconducting TMD moire heterojunction (Part 2)

ORAL

Abstract

Here we report the observation of an excitonic insulator, a correlated state with strongly bound electrons and holes, in an angle-aligned 1L-WS2/2L-WSe2 moiré superlattice. The moiré coupling induces a flat miniband on the valence-band side only in the 1st WSe2 layer interfacing WS2, barely affecting the 2nd WSe2 layer. The electrostatically introduced holes first fill this miniband and form a Mott insulator with a total carrier density corresponding to one hole per moiré supercell. By applying a vertical electric field, the valence band in the 2nd WSe2 layer can be tuned to overlap with the moiré miniband in the 1st WSe2 layer, realizing the coexistence of electrons and holes at equilibrium, as confirmed by optical spectroscopy measurements. The electron-hole pairs are bound as excitons due to a strong Coulomb interaction. We use microwave impedance microscopy to confirm the insulating nature of this exotic state in a dual-gate device geometry with monolayer graphene as top-gate. The microwave detection of embedded moiré heterojunction is enabled by the reduced conductivity in the graphene top-gate with applied magnetic field. This insulating state has also been observed in a back-gate only device geometry with finite electric field during hole doping. The excitonic insulator has a transition temperature as high as 90 K. Our study demonstrates a moiré system for the study of correlated many-body physics in two dimensions.

*X.H. and Y.-T.C. acknowledge support from NSF under award DMR-2104805.

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Publication: 1. Chen, D., Lian, Z., Huang, X. et al. Excitonic insulator in a heterojunction moiré superlattice. Nat. Phys. 18, 1171–1176 (2022).
2. Chen, D., Lian, Z., Huang, X. et al. Tuning moiré excitons and correlated electronic states through layer degree of freedom. Nat Commun 13, 4810 (2022).

Presenters

  • Xiong Huang

    • Columbia University

Authors

  • Xiong Huang

    • Columbia University

  • Zhen Lian

    • Rensselaer Polytechnic Institute
    • RPI

  • Dongxue Chen

    • Rensselaer Polytechnic Institute
    • Rensselaer polytechnic institute
    • RPI

  • Ying Su

    • University of Texas at Dallas
    • UT Dallas

  • Mina Rashetnia

    • University of California, Riverside

  • Mark Blei

    • Arizona State University
    • Arizona state university
    • ASU

  • Sefaattin Tongay

    • Arizona State University
    • FIAP

  • Yan Li

    • Rensselaer Polytechnic Institute
    • Rensselaer polytechnic institute
    • RPI

  • Lei Ma

    • Rensselaer Polytechnic Institute
    • Rensselaer polytechnic institute
    • RPI

  • Dmitry Smirnov

    • National High Magnetic Field Laboratory
    • National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA

  • Li Xiang

    • Florida State University
    • National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
    • National High Magnetic Field Laboratory

  • Zenghui Wang

    • University of Electronic Science and Technology of China
    • UESTC

  • Chuanwei Zhang

    • University of Texas at Dallas

  • Yongtao Cui

    • University of California, Riverside

  • Sufei Shi

    • Rensselaer Polytechnic Institute

  • Takashi Taniguchi

    • National Institute for Materials Science
    • Kyoto Univ
    • International Center for Materials Nanoarchitectonics, National Institute of Materials Science
    • Kyoto University
    • International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-044, Japan
    • International Center for Materials Nanoarchitectonics, National Institute for Materials Science
    • National Institute for Materials Science, Japan
    • National Institute For Materials Science
    • NIMS
    • National Institute for Material Science
    • International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
    • NIMS Japan

  • Kenji Watanabe

    • National Institute for Materials Science
    • Research Center for Functional Materials, National Institute of Materials Science
    • Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-044, Japan
    • NIMS
    • Research Center for Functional Materials, National Institute for Materials Science
    • National Institute for Materials Science, Japan
    • Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
    • NIMS Japan