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Twisted graphene multilayers are highly tunable flatband systems for developing new phases of matter. Here, we report an observation of Coulomb interaction driven first-order phase transitions and ferromagnetism in twisted double bilayer graphene (TDBG). The transitions are revealed in a series of step-like abrupt resistance jumps at the metal insulator transition due to van Hove instabilities when either the displacement field (D) or the carrier density (n) is swept across the halo boundary near the half filling. Consequently, prominent hysteresis loop appears as the D or n is tuned back and forth across the transition, indicating a formation of ordered domain. In addition, ferromagnetic first-order transitions with hysteresis are also observed at the magnetic field driven metal insulator transitions, where the nature of spin order is revealed in the identical magneto transport under both in-plane and out-of-plane directions. Moreover, we observe abundant first-order phase transitions between metal with preserved 4-fold symmetry and ferromagnetic metal with reduced 2- fold symmetry due to valley polarization, as well as the those between ferromagnetic metal and spin- polarized insulator, resulted from a competition between spin and orbital Zeeman effect at finite magnetic field. We interpret these first-order phase transitions in the picture of spin domain percolations driven by multi-field tunable Coulomb interactions, in agreement with Lifshitz transition from Hartree-Fock calculations. Our result enriches the correlated phase diagram in TDBG for discovering novel exotic phases and quantum phase transitions, and it would benefit other twisted moiré systems as well.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: Twisted graphene, quantum phase transitions, ferromagnetism

Date published: 2023-08-07

Publisher: American Physical Society (APS)

Journal:

• Physical Review X (ISSN: 21603308) vol. 13 issue. 3 031015

Funding:

• National Key Research and Development Program of China 2020YFA0309600
• National Key Research and Development Program of China 2021YFA1202900
• National Natural Science Foundation of China 61888102
• National Natural Science Foundation of China 11834017
• National Natural Science Foundation of China 12074413
• Chinese Academy of Sciences XDB30000000
• Chinese Academy of Sciences XDB33000000
• Special Project for Research and Development in Key areas of Guangdong Province 2020B0101340001
• Institute of Physics
• Ministry of Education, Culture, Sports, Science and Technology JPMXP0112101001
• Japan Society for the Promotion of Science 19H05790
• Japan Society for the Promotion of Science 20H00354
• Japan Society for the Promotion of Science 21H05233

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1103/physrevx.13.031015

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Updated at: 2025-02-28 16:30:34 +0900

Published on MDR: 2025-02-28 16:30:34 +0900