Observation of interband collective excitations in twisted bilayer graphene

Niels C.H. Hesp, Iacopo Torre, Daniel Rodan-Legrain, Pietro Novelli, Yuan Cao, Stephen Carr, Shiang Fang, Petr Stepanov, David Barcons-Ruiz, Hanan Herzig Sheinfux, Kenji Watanabe, Takashi Taniguchi, Dmitri K. Efetov, Efthimios Kaxiras, Pablo Jarillo-Herrero, Marco Polini, Frank H.L. Koppens

Research output: Contribution to journalArticlepeer-review

46 Scopus citations

Abstract

The single-particle and many-body properties of twisted bilayer graphene (TBG) can be dramatically different from those of a single graphene layer, particularly when the two layers are rotated relative to each other by a small angle (θ ≈ 1°), owing to the moiré potential induced by the twist. Here we probe the collective excitations of TBG with a spatial resolution of 20 nm, by applying mid-infrared near-field optical microscopy. We find a propagating plasmon mode in charge-neutral TBG for θ = 1.1−1.7°, which is different from the intraband plasmon in single-layer graphene. We interpret it as an interband plasmon associated with the optical transitions between minibands originating from the moiré superlattice. The details of the plasmon dispersion are directly related to the motion of electrons in the moiré superlattice and offer an insight into the physical properties of TBG, such as band nesting between the flat band and remote band, local interlayer coupling, and losses. We find a strongly reduced interlayer coupling in the regions with AA stacking, pointing at screening due to electron–electron interactions. Optical nano-imaging of TBG allows the spatial probing of interaction effects at the nanoscale and potentially elucidates the contribution of collective excitations to many-body ground states.

Original languageEnglish
Pages (from-to)1162-1168
Number of pages7
JournalNature Physics
Volume17
Issue number10
DOIs
StatePublished - Oct 2021
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2021, The Author(s), under exclusive licence to Springer Nature Limited.

Fingerprint

Dive into the research topics of 'Observation of interband collective excitations in twisted bilayer graphene'. Together they form a unique fingerprint.

Cite this