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Tunable spin and valley excitations of correlated insulators in Γ-valley moiré bands

Nature Materials volume 22, pages 731–736 (2023)Cite this article

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Abstract

Moiré superlattices formed from transition metal dichalcogenides support a variety of quantum electronic phases that are highly tunable using applied electromagnetic fields. While the valley degree of freedom affects optoelectronic properties in the constituent transition metal dichalcogenides, it has yet to be fully explored in moiré systems. Here we establish twisted double-bilayer WSe2 as an experimental platform to study electronic correlations within Γ-valley moiré bands. Through local and global electronic compressibility measurements, we identify charge-ordered phases at multiple integer and fractional moiré fillings. By measuring the magnetic field dependence of their energy gaps and the chemical potential upon doping, we reveal spin-polarized ground states with spin-polaron quasiparticle excitations. In addition, an applied displacement field induces a metal–insulator transition driven by tuning between Γ- and K-valley moiré bands. Our results demonstrate control over the spin and valley character of the correlated ground and excited states in this system.

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Fig. 1: Γ-valley moiré bands in tdWSe2.
Fig. 2: Magnetic field dependence of correlated insulating ground states and their excitations.
Fig. 3: Displacement field dependence of correlated insulators.

Data availability

Source data are provided with this paper. Additional data that support the findings of this study are available from the corresponding author upon reasonable request.

Code availability

The codes that support the findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We acknowledge helpful conversations with A.H. MacDonald. We thank T. Heinz, A. O’Beirne and H.B. Ribeiro for their assistance with second-harmonic generation measurements. Experimental work was primarily supported by the National Science Foundation (Grant no. NSF-DMR-2103910). B.E.F. acknowledges an Alfred P. Sloan Foundation Fellowship and a Cottrell Scholar Award. The work at the Massachusetts Institute of Technology is supported by a Simons Investigator Award from the Simons Foundation. L.F. is partly supported by the David and Lucile Packard Foundation. K.W. and T.T. acknowledge support from the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (JSPS KAKENHI, Grant nos. 19H05790, 20H00354 and 21H05233). B.A.F. acknowledges a Stanford Graduate Fellowship. Part of this work was performed at the Stanford Nano Shared Facilities, supported by the National Science Foundation (Award no. ECCS-2026822).

Author information

Author notes

  1. These authors contributed equally: Benjamin A. Foutty, Jiachen Yu, Trithep Devakul.

Authors and Affiliations

  1. Geballe Laboratory for Advanced Materials, Stanford, CA, USA

    Benjamin A. Foutty, Jiachen Yu, Carlos R. Kometter & Benjamin E. Feldman

  2. Department of Physics, Stanford University, Stanford, CA, USA

    Benjamin A. Foutty, Carlos R. Kometter & Benjamin E. Feldman

  3. Department of Applied Physics, Stanford University, Stanford, CA, USA

    Jiachen Yu

  4. Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA

    Trithep Devakul, Yang Zhang & Liang Fu

  5. Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, USA

    Yang Zhang

  6. Min H. Kao Department of Electrical Engineering and Computer Science, University of Tennessee, Knoxville, TN, USA

    Yang Zhang

  7. Research Center for Functional Materials, National Institute for Material Science, Tsukuba, Japan

    Kenji Watanabe

  8. International Center for Materials Nanoarchitectonics, National Institute for Material Science, Tsukuba, Japan

    Takashi Taniguchi

  9. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA

    Benjamin E. Feldman

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  1. Benjamin A. Foutty
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Contributions

B.A.F, J.Y. and B.E.F. designed and conducted the scanning SET experiments. B.A.F. and B.E.F. designed and conducted the dual-gate capacitance experiments. T.D., Y.Z. and L.F. conducted theoretical calculations. B.A.F. fabricated the samples, with help from C.R.K. K.W. and T.T. provided hBN crystals. All authors participated in analysis of the data and writing of the paper.

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Correspondence to Benjamin E. Feldman.

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Nature Materials thanks Emanuel Tutuc and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Foutty, B.A., Yu, J., Devakul, T. et al. Tunable spin and valley excitations of correlated insulators in Γ-valley moiré bands. Nat. Mater. 22, 731–736 (2023). https://doi.org/10.1038/s41563-023-01534-z

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