Spin skyrmion gaps as signatures of strong-coupling insulators in magic-angle twisted bilayer graphene

Jiachen Yu, Benjamin A. Foutty, Yves H. Kwan, Mark E. Barber, Kenji Watanabe, Takashi Taniguchi, Zhi-Xun Shen, Siddharth A. Parameswaran and Benjamin E. Feldman ()
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Jiachen Yu: Stanford University
Benjamin A. Foutty: Geballe Laboratory of Advanced Materials
Yves H. Kwan: University of Oxford
Mark E. Barber: Stanford University
Kenji Watanabe: National Institute for Materials Science, 1-1 Namiki
Takashi Taniguchi: National Institute for Materials Science, 1-1 Namiki
Zhi-Xun Shen: Stanford University
Siddharth A. Parameswaran: University of Oxford
Benjamin E. Feldman: Geballe Laboratory of Advanced Materials

Nature Communications, 2023, vol. 14, issue 1, 1-7

Abstract: Abstract The flat electronic bands in magic-angle twisted bilayer graphene (MATBG) host a variety of correlated insulating ground states, many of which are predicted to support charged excitations with topologically non-trivial spin and/or valley skyrmion textures. However, it has remained challenging to experimentally address their ground state order and excitations, both because some of the proposed states do not couple directly to experimental probes, and because they are highly sensitive to spatial inhomogeneities in real samples. Here, using a scanning single-electron transistor, we observe thermodynamic gaps at even integer moiré filling factors at low magnetic fields. We find evidence of a field-tuned crossover from charged spin skyrmions to bare particle-like excitations, suggesting that the underlying ground state belongs to the manifold of strong-coupling insulators. From the spatial dependence of these states and the chemical potential variation within the flat bands, we infer a link between the stability of the correlated ground states and local twist angle and strain. Our work advances the microscopic understanding of the correlated insulators in MATBG and their unconventional excitations.

Date: 2023
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DOI: 10.1038/s41467-023-42275-6

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