Comment on "Electron spin resonance and collective excitations in magic-angle twisted bilayer graphene"

TL;DR

This comment critiques a recent study claiming to observe collective excitations in magic-angle twisted bilayer graphene, arguing that similar features are already known in simpler graphene systems and that their theoretical interpretation is flawed.

Contribution

The comment clarifies that the observed resonance features are not unique to twisted bilayer graphene and provides a simpler, single-particle explanation that was overlooked in the original paper.

Findings

Resonance features are common in mono- and few-layer graphene.

Single-particle band structure explains the observed resonances.

Original interpretation of collective excitations is challenged.

Abstract

This comment pertains the recent manuscript by Morissette {\it et al.} [arXiv:2206.08354v1]. The authors claim to have found signatures of collective excitations in electron spin resonance experiments that would be linked to the correlated structure of magic angle bilayer graphene. However, identical resonance features have already been reported in previous works on mono- and few-layer graphene, voiding their theoretical framework. A straight forward theoretical picture within the single-particle topologically non-trivial band structure of graphene delivers satisfactory explanations for the observation of the resonant features and applies as well to the data presented by Morissette {\it et al.}. However, this intuitive picture has been disregarded by the authors.