Gate-tuning of graphene plasmons revealed by infrared nano-imaging

TL;DR

This study demonstrates that graphene plasmons can be actively tuned using gate voltage, with infrared nano-imaging revealing their propagation, wavelength, and loss characteristics, surpassing traditional metal plasmonic devices.

Contribution

It provides the first explicit demonstration of gate-tunable surface plasmons in graphene with detailed imaging and analysis of their properties and losses.

Findings

Graphene plasmons have a wavelength of about 200 nm at infrared frequencies.

Gate voltage can alter both the amplitude and wavelength of graphene plasmons.

Graphene plasmons exhibit lower dissipation compared to metal-based plasmonic structures.

Abstract

Surface plasmons are collective oscillations of electrons in metals or semiconductors enabling confinement and control of electromagnetic energy at subwavelength scales. Rapid progress in plasmonics has largely relied on advances in device nano-fabrication, whereas less attention has been paid to the tunable properties of plasmonic media. One such medium-graphene-is amenable to convenient tuning of its electronic and optical properties with gate voltage. Through infrared nano-imaging we explicitly show that common graphene/SiO2/Si back-gated structures support propagating surface plasmons. The wavelength of graphene plasmons is of the order of 200 nm at technologically relevant infrared frequencies, and they can propagate several times this distance. We have succeeded in altering both the amplitude and wavelength of these plasmons by gate voltage. We investigated losses in graphene using plasmon interferometry: by exploring real space profiles of plasmon standing waves formed between the tip of our nano-probe and edges of the samples. Plasmon dissipation quantified through this analysis is linked to the exotic electrodynamics of graphene. Standard plasmonic figures of merits of our tunable graphene devices surpass that of common metal-based structures.