Hyperbolic Plasmons in Coupled Luttinger Liquids of Homochiral Carbon Nanotube Arrays

A Luttinger liquid is a theoretical model describing interacting electrons in one-dimensional (1D) conductors. While individual 1D conductors have shown interesting Luttinger-liquid behaviors such as spin–charge separation and power-law spectral density, the more interesting phenomena predicted in coupled Luttinger liquids of neighboring 1D conductors have been rarely observed due to the difficulty in creating such structures. Recently, we have successfully grown close-packed carbon nanotube (CNT) arrays with uniform chirality, providing an ideal material system for studying the coupled Luttinger liquids. Here, we report on the observation of tunable hyperbolic plasmons in the coupled Luttinger liquids of CNT arrays using scanning near-field optical microscopy. These hyperbolic plasmons, resulting from the conductivity anisotropy in the CNT array, exhibit strong spatial confinement, in situ tunability, and a wide spectral range. Despite their hyperbolic wavefronts, the plasmon propagation in the axial direction still adheres to the Luttinger-liquid theory. Our work not only demonstrates a fascinating phenomenon in coupled Luttinger liquids for fundamental physics exploration, but also provides a highly confined and in situ tunable hyperbolic plasmon in close-packed CNT arrays for future nanophotonic devices and circuits.