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

Understand

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 moir\'e 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.