Uncovering the spin ordering in magic-angle graphene via edge state equilibration

Jesse C. Hoke; Yifan Li; Julian May-Mann; Kenji Watanabe; Takashi Taniguchi; Barry Bradlyn; Taylor L. Hughes; Benjamin E. Feldman

doi:10.1038/s41467-024-48385-z

Journal article Uncovering the spin ordering in magic-angle graphene via edge state equilibration

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Jesse C. Hoke, Yifan Li, Julian May-Mann, Kenji Watanabe, Takashi Taniguchi, Barry Bradlyn, Taylor L. Hughes, Benjamin E. Feldman. Uncovering the spin ordering in magic-angle graphene via edge state equilibration. Nature Communications. 2024, 15 (1), 4321. https://doi.org/10.1038/s41467-024-48385-z

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Determining the symmetry breaking order of correlated quantum phases is essential for under- standing the microscopic interactions in their host systems. The flat bands in magic-angle twisted bilayer graphene (MATBG) provide an especially rich arena to investigate such interaction- driven ground states, and while progress has been made in identifying the correlated insulators and their excitations at commensurate moir ́e filling factors, the spin-valley polarization of the Chern insulators that emerge at high fields remains unknown. Here we intro- duce a new technique based on twist-decoupled van der Waals layers that enables measurements of their chemical potentials and, by studying the backscattering between counter-propagating edge states, determination of their relative spin polarization. Applying this method to twist-decoupled MATBG and monolayer graphene, we find that the quantum Hall states near the charge neutrality point in MATBG favor spin-unpolarized states at even integer filling factors. The measurements also indicate that the correlated Chern insulator emerging from half filling of the flat valence band is spin-unpolarized, but suggest that its conduction band counterpart may be spin-polarized. Our results constrain models of spin-valley ordering in MATBG and establish a versatile approach to study the electronic properties of van der Waals systems.

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