Abstract:
Carbon nanotubes provide a rare access point into the plasmon physics of one-dimensional electronic systems that operate as terahertz and infrared antennas at deep subwavelength scales. By assembling purified nanotubes into uniformly sized arrays, we show that they support coherent plasmon resonances, that these plasmons couple to nanotube and substrate phonons, and that the resulting phonon-plasmon resonances have quality factors as high as 10. The problem of limited absorption provided by these thin film arrays is addressed by assembling much thicker films of aligned and uniformly-sized carbon nanotubes, and showing that their plasmon resonances are strong, narrow, and broadly tunable. These thick arrays exhibit peak attenuation reaching 70% with resonator quality factors approaching that of their thinner counterparts. These resonators are strongly blue-shifted with increasing film thickness, allowing resonant wavelengths as small at 1.4 μm to be attained, well within the technologically important infrared telecom band. In addition, by further improving the assembling process, we crystallized carbon nanotubes into chip-scale superlattices and that this new material enables intrinsically ultrastrong light-matter interactions: rather than coupling to external cavities, nanotube excitons interact with the infrared light confined by the Fabry–Pérot plasmon resonances of the nanotubes themselves. Our crystals of nanotubes have a hexagonal lattice structure and domain sizes exceeding 30 nm. The extremely high nanotube density allows plasmon-exciton coupling strengths to reach 0.5 eV, which is 75% of the bare exciton energy and a record among room-temperature systems. Intrinsically ultrastrong light-matter interactions provide a compelling foundation for active nanophotonic devices like low-power optical switches, tunable metamaterials, and thresholdless nanolasers.