Multiple Tunable Hyperbolic Resonances in Broadband Infrared Carbon-Nanotube Metamaterials

TL;DR

This paper demonstrates multiple tunable hyperbolic resonances in broadband infrared carbon nanotube metamaterials, combining experimental near-field and far-field studies with theoretical modeling to reveal their potential for infrared applications.

Contribution

It reports the first observation of multiple hyperbolic plasmon resonances in aligned carbon nanotube metamaterials and links these to higher-order Fabry-Pérot waveguide modes.

Findings

Broadband extinction from 1.5-10 μm in nanotube resonator arrays

Reversible switching of extinction in the 3-5 μm atmospheric window

Agreement between experimental results and theoretical Fabry-Pérot mode modeling

Abstract

Aligned, densely-packed carbon nanotube metamaterials prepared using vacuum filtration are an emerging infrared nanophotonic material. We report multiple hyperbolic plasmon resonances, together spanning the mid-infrared, in individual resonators made from aligned and densely-packed carbon nanotubes. In the first near-field scanning optical microscopy (NSOM) imaging study of nanotube metamaterial resonators, we observe distinct deeply-subwavelength field profiles at the fundamental and higher-order resonant frequencies. The wafer-scale area of the nanotube metamaterials allows us to combine this near-field imaging with a systematic far-field spectroscopic study of the scaling properties of many resonator arrays. Thorough theoretical modeling agrees with these measurements and identifies the resonances as higher-order Fabry-P\'erot (FP) resonances of hyperbolic waveguide modes. Nanotube resonator arrays show broadband extinction from 1.5-10 {\mu}m and reversibly switchable extinction in the 3-5 {\mu}m atmospheric transparency window through the coexistence of multiple modes in individual ribbons. Broadband carbon nanotube metamaterials supporting multiple resonant modes are a promising candidate for ultracompact absorbers, tunable thermal emitters, and broadband sensors in the mid-infrared.