Broadly Tunable Unidirectional Hyperbolic Metasurfaces of Ultrathin Periodically Aligned Carbon Nanotubes

Self-assembled quasiperiodic finite-thickness single-wall carbon nanotube (SWCN) films have been recently shown experimentally to exhibit extraordinary optoplasmonic properties [1-3], which is why they are getting more and more attention of experimental communities. Here, we study theoretically the intrinsic collective quasiparticle excitations responsible for the in-plane electro-magnetic (EM) response of ultrathin plane-parallel periodic SWCN arrays and weakly inhomogeneous SWCN films [4,5]. Using the low-energy plasmon response calculation technique along with the many-particle Green’s function formalism in the Matsubara formulation, we derive the in-plane dynamical EM response tensor of the system in the broad spectral domain of IR to visible. We show that the EM response can be controlled by the volume fraction of constituent SWCNs, the active component of the film, and that this can be done not only by varying the parameters of the SWCN content (CN diameter and/or intertube distance) but also by merely varying the thickness of the CN embedding dielectric layer. For homogeneous single-type periodic SWCN arrays and weakly inhomogeneous multi-type quasi-periodic SWCN films, the real part of the EM response function in the CN alignment direction is negative for a sufficiently wide domain in the neighborhood of a quantum interband<br/>transition of the constituent SWCN, to form a relatively broad negative refraction (NR) band. The system behaves as a unidirectional hyperbolic metamaterial at higher frequencies than those (typically in the IR) the classical intraband plasma oscillations have to offer. By decreasing the CN diameter it is quite possible to push this unidirectional NR band in the visible, and using weakly inhomogeneous multi-type SWCN films can make it even broader than the NR band of the single-type SWCN array. We also show that for a properly fabricated two-component SWCN film, by varying the relative weights of the two constituent CN array components, it is possible to tune the optical absorption profile to make the film transmit or absorb light in the neighborhood of an exciton absorption resonance on-demand [5].<br/><br/>Acknowledgements: U.S. National Science Foundation Award No. DMR-1830874 (I.V.B.)<br/><br/>References:<br/>[1] J.A. Roberts, P.-H. Ho, S.-J. Yu, X. Wu, et al., Phys. Rev. Appl. 14, 044006 (2020).<br/>[2] W. Gao, C.F. Doiron, X. Li, J. Kono, and G.V. Naik, ACS Photonics 6, 1602 (2019).<br/>[3] J.A. Roberts, S.-J. Yu, P.-H. Ho, S. Schoeche, A.L. Falk, and J.A. Fan, Nano Lett. 19, 3131 (2019).<br/>[4] I.V. Bondarev and C.M. Adhikari, Phys. Rev. Appl. 15, 034001 (2021).<br/>[5] C.M. Adhikari and I.V. Bondarev, J. Appl. Phys. 129, 015301 (2021).