We study theoretically confinement related effects in the optical response of thin plasmonic films of controlled variable thickness. While being constant for relatively thick films, the plasma frequency is shown to acquire spatial dispersion typical of two-dimensional materials such as graphene, gradually shifting to the red with the film thickness reduction. The dissipative loss, while decreasing at any fixed frequency, gradually goes up at the plasma frequency as it shifts to the red with the film thickness reduced. These features offer a controllable way to tune spatial dispersion and related optical properties of plasmonic films and metasurfaces on demand, by precisely controlling their thickness, material composition, and by choosing deposition substrates and coating layers appropriately.

We study theoretically the interactions of excitonic states with surface electromagnetic modes of small-diameter ( < ∼ 1 nm) semiconducting single-walled carbon nanotubes. We show that these interactions can result in strong exciton-surface-plasmon coupling. The exciton absorption line shape exhibits Rabi splitting ∼ 0.1 eV as the exciton energy is tuned to the nearest interband surface plasmon resonance of the nanotube. We also show that the quantum confined Stark effect may be used as a tool to control the exciton binding energy and the nanotube band gap in carbon nanotubes in order, e. g., to bring the exciton total energy in resonance with the nearest interband plasmon mode. The exciton-plasmon Rabi splitting we predict here for an individual carbon nanotube is close in its magnitude to that previously reported for hybrid plasmonic nanostructures artificially fabricated of organic semiconductors on metallic films. We expect this effect to open up paths to new tunable optoelectronic device applications of semiconducting carbon nanotubes.

We report a strictly non-exponential spontaneous decay dynamics of an excited two-level atom placed inside or at different distances outside a carbon nanotube (CN). This is the result of strong non-Markovian memory effects arising from the rapid variation of the photonic density of states with frequency near the CN. The system exhibits vacuum-field Rabi oscillations, a principal signature of strong atom-vacuum-field coupling, when the atom is close enough to the nanotube surface and the atomic transition frequency is in the vicinity of the resonance of the photonic density of states. Caused by decreasing the atom-field coupling strength, the non-exponential decay dynamics gives place to the exponential one if the atom moves away from the CN surface. Thus, atom-field coupling and the character of the spontaneous decay dynamics, respectively, may be controlled by changing the distance between the atom and CN surface by means of a proper preparation of atomically doped CNs. This opens routes for new challenging nanophotonics applications of atomically doped CN systems as various sources of coherent light emitted by dopant atoms.

The spontaneous decay process of an excited atom placed inside or outside a carbon nanotube is analyzed. Calculations have been performed for various achiral nanotubes. The effect of the nanotube surface is shown to increase the atomic spontaneous decay rate by up to 6 orders of magnitude compared with that of the same atom in vacuum. This increase is associated with nonradiative decay via surface excitations in the nanotube.

We use quantum electrodynamics and the confinement-induced nonlocal dielectric response model based on the Keldysh-Rytova electron interaction potential to study the epsilon-near-zero modes of metallic films in the transdimensional regime. New peculiar effects are revealed such as the plasmon mode degeneracy lifting and the dipole emitter coupling to the split epsilon-near-zero modes, leading to biexponential spontaneous decay with up to three-orders-of-magnitude increased rates.Transdimensional (TD) materials are ultrathin planar nanostructures composed of a precisely controlled finite number of monolayers [1]. Modern material fabrication techniques allow one to produce stoichiometrically perfect films of metals and semiconductors down to a few, or even a single monolayer in thickness [2][3][4][5][6]. TD materials make it possible to probe fundamental properties of light-matter interactions as they evolve from a single atomic layer to a larger number of layers approaching the bulk material properties. The current research has been largely focusing on either purely 2D structures including metal-dielectric interfaces and novel 2D materials [7,8], or on conventional bulk materials, being guided by the traditional view that only the dimensionality and chemical composition are important to control the optoelectronic properties of materials. The transitional, transdimensional regime laying in between 3D and 2D, has been largely out of the major research focus so far.Ultrathin films made of metals, doped semiconductors, or polar materials with a thickness of only a few atomic layers, can support plasmon-, exciton-, and phonon-polariton eigenmodes [6][7][8][9][10][11][12][13]. Such TD materials are therefore expected to show the high tailorability of their electronic and optical properties by varying their thickness (number of monolayers), chemical, atomic and electronic composition (stoichiometry, doping) as opposed to conventional thin films usually described by the bulk material properties with boundary conditions imposed. Plasmonic TD materials (ultrathin finite-thickness metallic films), in particular, can provide controlled light confinement due to their thicknessdependent localized surface plasmon (SP) modes [12,13], thereby offering tunable light-matter coupling, higher adjustable transparency and new quantum phenomena such as enabling atomic transitions that are normally forbidden [14]. Similar to truly 2D and quasi-2D materials such as graphene and transition metal dichalcogenide monolayers [8,15], plasmonic TD materials are also expected to show the extreme sensitivity to external fields, making possible advances such as novel parity-time symmetry * Corresponding author email: ibondarev@nccu.edu breaking photonic designs [16] that can further develop the fields of plasmonics and optical metasurfaces [17,18]. However, while some predictions on tunability, anomalous dispersion, and strong light confinement in ultrathin plasmonic films have been made [19][20][21][22][23] much remains unclear about their nonlinea...