Real-space imaging of the tailored plasmons in twisted bilayer graphene

TL;DR

This study uses real-space nanoimaging to explore how twist angles in bilayer graphene influence its plasmonic properties, revealing angle-dependent confinement and damping effects linked to electronic interactions.

Contribution

It provides the first systematic real-space imaging of plasmons in twisted bilayer graphene across various twist angles, highlighting the role of Fermi-velocity renormalization.

Findings

Plasmon wavelength varies with twist angle.

Lower damping observed at larger twist angles.

Fermi-velocity renormalization explains plasmon behavior.

Abstract

We report a systematic plasmonic study of twisted bilayer graphene (TBLG) - two graphene layers stacked with a twist angle. Through real-space nanoimaging of TBLG single crystals with a wide distribution of twist angles, we find that TBLG supports confined infrared plasmons that are sensitively dependent on the twist angle. At small twist angles, TBLG has a plasmon wavelength comparable to that of single-layer graphene. At larger twist angles, the plasmon wavelength of TBLG increases significantly with apparently lower damping. Further analysis and modeling indicate that the observed twist-angle dependence of TBLG plasmons in the Dirac linear regime is mainly due to the Fermi-velocity renormalization, a direct consequence of interlayer electronic coupling. Our work unveils the tailored plasmonic characteristics of TBLG and deepens our understanding of the intriguing nano-optical physics in novel van der Waals coupled two-dimensional materials.