Collective Excitations and Optical Response of Ultrathin Carbon Nanotube Films

TL;DR

This paper theoretically investigates the electromagnetic response of ultrathin carbon nanotube films, revealing how their collective excitations can be tuned by film composition and thickness, leading to hyperbolic metamaterial behavior and negative refraction.

Contribution

It introduces a theoretical framework for controlling the optical response of nanotube films through structural parameters, enabling tunable hyperbolic metamaterials and negative refraction in visible frequencies.

Findings

Negative refraction band near quantum interband transition

Hyperbolic metamaterial behavior at high frequencies

Tuning negative refraction into visible spectrum by decreasing nanotube diameter

Abstract

We present a theoretical study of the collective quasiparticle excitations responsible for the electromagnetic response of ultrathin plane-parallel homogeneous periodic single-wall carbon nanotube arrays and weakly inhomogeneous single-wall carbon nanotube films. We show that in addition to varying film composition, the collective response can be controlled by varying the film thickness. For single-type nanotube arrays, the real part of the dielectric response shows a broad negative refraction band near a quantum interband transition of the constituent nanotube, whereby the system behaves as a hyperbolic metamaterial at higher frequencies than those classical plasma oscillations have to offer. By decreasing nanotube diameters it is possible to push this negative refraction into the visible region, and using weakly inhomogeneous multi-type nanotube films broadens its bandwidth.