Evidence of frustrated magnetic interactions in a Wigner-Mott insulator

Yanhao Tang; Kaixiang Su; Lizhong Li; Yang Xu; Song Liu; Kenji Watanabe; Takashi Taniguchi; James Hone; Chao-Ming Jian; Cenke Xu; Kin Fai Mak; Jie Shan

doi:10.1038/s41565-022-01309-8

Evidence of frustrated magnetic interactions in a Wigner-Mott insulator

Nat Nanotechnol. 2023 Mar;18(3):233-237. doi: 10.1038/s41565-022-01309-8. Epub 2023 Jan 16.

Authors

Yanhao Tang^{1

2}, Kaixiang Su³, Lizhong Li¹, Yang Xu¹, Song Liu⁴, Kenji Watanabe⁵, Takashi Taniguchi⁵, James Hone⁴, Chao-Ming Jian⁶, Cenke Xu³, Kin Fai Mak^{7

8

9}, Jie Shan^{10

11

12}

Affiliations

¹ School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA.
² Interdisciplinary Center for Quantum Information, Zhejiang Province Key Laboratory of Quantum Technology, and Department of Physics, Zhejiang University, Hangzhou, China.
³ Department of Physics, University of California, Santa Barbara, CA, USA.
⁴ Department of Mechanical Engineering, Columbia University, New York, NY, USA.
⁵ National Institute for Materials Science, Tsukuba, Japan.
⁶ Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA.
⁷ School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA. kinfai.mak@cornell.edu.
⁸ Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA. kinfai.mak@cornell.edu.
⁹ Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA. kinfai.mak@cornell.edu.
¹⁰ School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA. jie.shan@cornell.edu.
¹¹ Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA. jie.shan@cornell.edu.
¹² Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA. jie.shan@cornell.edu.

PMID: 36646827
DOI: 10.1038/s41565-022-01309-8

Abstract

Electrons in two-dimensional semiconductor moiré materials are more delocalized around the lattice sites than those in conventional solids^1,2. The non-local contributions to the magnetic interactions can therefore be as important as the Anderson superexchange³, which makes the materials a unique platform to study the effects of competing magnetic interactions^3,4. Here we report evidence of strongly frustrated magnetic interactions in a Wigner-Mott insulator at a two-thirds (2/3) filling of the moiré lattice in angle-aligned WSe₂/WS₂ bilayers. Magneto-optical measurements show that the net exchange interaction is antiferromagnetic for filling factors below 1 with a strong suppression at a 2/3 filling. The suppression is lifted on screening of the long-range Coulomb interactions and melting of the Wigner-Mott insulators by a nearby metallic gate. The results can be qualitatively captured by a honeycomb-lattice spin model with an antiferromagnetic nearest-neighbour coupling and a ferromagnetic second-neighbour coupling. Our study establishes semiconductor moiré materials as a model system for lattice-spin physics and frustrated magnetism⁵.