Evidence of frustrated magnetic interactions in a Wigner–Mott insulator

Two-dimensional semiconductor moiré materials have emerged as a highly controllable platform to simulate and explore quantum condensed matter 1-19 . Compared to real solids, electrons in semiconductor moiré materials are less strongly attracted to the moiré lattice sites 1, 2 , making the nonlocal contributions to the magnetic interactions as important as the Anderson super-exchange 20 . It provides a unique platform to study the effects of competing magnetic interactions 20, 21 . Here, we report the observation of strongly frustrated magnetic interactions in a Wigner-Mott insulating state at 2/3 filling of the moiré lattice in angle-aligned WSe 2 /WS 2 heterobilayers. Magneto-optical measurements show that the net exchange interaction is antiferromagnetic for filling factors below 1 with a strong suppression at 2/3 filling. The suppression is lifted upon screening of the long-range Coulomb interactions and melting of the Wigner-Mott insulator by a nearby metallic gate. The results can be qualitatively captured by a honeycomb-lattice spin model with an antiferromagnetic nearest-neighbor coupling and a ferromagnetic second-neighbor coupling. Our study establishes semiconductor moiré materials as a model system for the lattice-spin physics and frustrated magnetism 22 . Moiré materials formed by semiconducting

[1]  Xiaoqin Li,et al.  Excitons in semiconductor moiré superlattices , 2022, Nature Nanotechnology.

[2]  J. Shan,et al.  Dielectric catastrophe at the Wigner-Mott transition in a moiré superlattice , 2022, Nature Communications.

[3]  Kenji Watanabe,et al.  Correlated interlayer exciton insulator in heterostructures of monolayer WSe2 and moiré WS2/WSe2 , 2021, Nature Physics.

[4]  A. MacDonald,et al.  Nonlocal Interactions in Moiré Hubbard Systems. , 2021, Physical review letters.

[5]  J. Shan,et al.  Excitons and emergent quantum phenomena in stacked 2D semiconductors , 2021, Nature.

[6]  Kenji Watanabe,et al.  Imaging two-dimensional generalized Wigner crystals , 2021, Nature.

[7]  J. Shan,et al.  Dipolar excitonic insulator in a moiré lattice , 2021, Nature Physics.

[8]  Nai Chao Hu,et al.  Competing magnetic states in transition metal dichalcogenide moiré materials , 2021, Physical Review B.

[9]  T. Devakul,et al.  Spin-textured Chern bands in AB-stacked transition metal dichalcogenide bilayers , 2021, Proceedings of the National Academy of Sciences.

[10]  J. Shan,et al.  Quantum anomalous Hall effect from intertwined moiré bands , 2021, Nature.

[11]  T. Devakul,et al.  Magic in twisted transition metal dichalcogenide bilayers , 2021, Nature Communications.

[12]  Yang Zhang,et al.  Electronic structures, charge transfer, and charge order in twisted transition metal dichalcogenide bilayers , 2021 .

[13]  A. Millis,et al.  Quantum Criticality in Twisted Transition Metal Dichalcogenides , 2021 .

[14]  J. Shan,et al.  Continuous Mott transition in semiconductor moiré superlattices , 2021, Nature.

[15]  J. Shan,et al.  Charge-order-enhanced capacitance in semiconductor moiré superlattices , 2021, Nature Nanotechnology.

[16]  A. Georges,et al.  Moiré heterostructures as a condensed-matter quantum simulator , 2020, Nature Physics.

[17]  J. Shan,et al.  Stripe phases in WSe2/WS2 moiré superlattices , 2020, Nature Materials.

[18]  J. Shan,et al.  Correlated insulating states at fractional fillings of moiré superlattices , 2020, Nature.

[19]  S. Das Sarma,et al.  Quantum phase diagram of a Moiré-Hubbard model , 2020, Physical Review B.

[20]  Kenji Watanabe,et al.  Correlated insulating states at fractional fillings of the WS2/WSe2 moiré lattice , 2020, Nature Physics.

[21]  Kenji Watanabe,et al.  Correlated electronic phases in twisted bilayer transition metal dichalcogenides , 2020, Nature Materials.

[22]  S. Das Sarma,et al.  Band topology, Hubbard model, Heisenberg model, and Dzyaloshinskii-Moriya interaction in twisted bilayer WSe2 , 2020, 2004.04168.

[23]  T. Taniguchi,et al.  Strongly correlated electrons and hybrid excitons in a moiré heterostructure , 2020, Nature.

[24]  K. Slagle,et al.  Charge transfer excitations, pair density waves, and superconductivity in moiré materials , 2020, Physical Review B.

[25]  J. Shan,et al.  Simulation of Hubbard model physics in WSe2/WS2 moiré superlattices , 2020, Nature.

[26]  Kenji Watanabe,et al.  Mott and generalized Wigner crystal states in WSe2/WS2 moiré superlattices , 2019, Nature.

[27]  N. Yuan,et al.  Moiré quantum chemistry: Charge transfer in transition metal dichalcogenide superlattices , 2019, Physical Review B.

[28]  Kenji Watanabe,et al.  Observation of moiré excitons in WSe2/WS2 heterostructure superlattices , 2018, Nature.

[29]  A. MacDonald,et al.  Topological Insulators in Twisted Transition Metal Dichalcogenide Homobilayers. , 2018, Physical review letters.

[30]  J. Shan,et al.  Light–valley interactions in 2D semiconductors , 2018, Nature Photonics.

[31]  E. Tutuc,et al.  Hubbard Model Physics in Transition Metal Dichalcogenide Moiré Bands. , 2018, Physical review letters.

[32]  Wang Yao,et al.  Spin and pseudospins in layered transition metal dichalcogenides , 2014, Nature Physics.

[33]  L. Balents.  Spin liquids in frustrated magnets , 2010, Nature.

[34]  B. Powell,et al.  Ferromagnetism, paramagnetism, and a Curie-Weiss metal in an electron-doped Hubbard model on a triangular lattice , 2005, cond-mat/0512696.

[35]  Rajiv R. P. Singh,et al.  Temperature dependence of the magnetic susceptibility for triangular-lattice antiferromagnets with spatially anisotropic exchange constants , 2004, cond-mat/0410381.

[36]  R. Cava,et al.  Charge ordering, commensurability, and metallicity in the phase diagram of the layered NaxCoO2. , 2003, Physical Review Letters.

[37]  Lewicki,et al.  Magnetic susceptibility of semimagnetic semiconductors: The high-temperature regime and the role of superexchange. , 1986, Physical review. B, Condensed matter.