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New phases of matter can be stabilized by a combination of diverging electronic density of states, strong interactions, and spin-orbit coupling. Recent experiments in magic-angle twisted bilayer graphene (TBG) have uncovered a wealth of novel phases as a result of interaction-driven spin-valley flavour polarization. In this work, we explore correlated phases appearing due to the combined effect of spin-orbit coupling-enhanced valley polarization and large density of states below half filling (ν ≲ 2) of the moiré band in a TBG coupled to tungsten diselenide. We observe anomalous Hall effect, accompanied by a series of Lifshitz transitions, that are highly tunable with carrier density and magnetic field. Strikingly, the magnetization shows an abrupt sign change in the vicinity of half-filling, confirming its orbital nature. The coercive fields reported are about an order of magnitude higher than previous studies in graphene-based moiré systems, presumably aided by a Stoner instability favoured by the van Hove singularities in the malleable bands. While the Hall resistance is not quantized at zero magnetic fields, indicative of a ground state with partial valley polarization, perfect quantization and complete valley polarization are observed at finite fields. Our findings illustrate that singularities in the flat bands in the presence of spin-orbit coupling can stabilize ordered phases even at non-integer moiré band fillings.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: Spin-orbit coupling, anomalous Hall effect, Lifshitz transitions

Date published: 2023-07-08

Publisher: Springer Science and Business Media LLC

Journal:

• Nature Communications (ISSN: 20411723) vol. 14 issue. 1 4055

Funding:

• DST | Science and Engineering Research Board SPG/2020/000164
• DST | Science and Engineering Research Board WEA/2021/000005

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

MDR DOI:

First published URL: https://doi.org/10.1038/s41467-023-39855-x

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Updated at: 2025-02-15 12:31:01 +0900

Published on MDR: 2025-02-15 12:31:01 +0900