We show that hexagonal boron nitride (hBN), a two-dimensional insulator supports tunable excitons in the near and middle ultraviolet if subjected to an external superlattice potential. Our calculations predict that as we increase the strength of the potential, the gap reduces, and the anisotropy of the dispersion is enhanced. Consequently, the binding-energies of the excitons decrease, leading to a red-shift of the excitonic levels. We also observe that the absorption is reduced when we change the polarization from along the periodicity of the potential to perpendicular to it, with the system acting as an optical polarizer. As we reduce the gap, the characteristic frequency range for which we can excite exciton-polaritons red-shifts as well. These modes behave quite differently from pristine hBN in extreme cases where the anisotropy of the system grows indefinitely. In this way, by tuning the potential, we can manipulate the excitonic and sub-gap optical properties of hBN.
Bismuth chalcogenides have emerged as an intriguing option in nanophotonics due to their unique properties, including a significant dielectric function and topologically protected surface states in the terahertz (THz) range. Our study focuses on the optical response of Bi2Se3 topological-insulator nanospheres, where topological properties arise, influencing electromagnetic modes and field enhancement. Within a fully electrodynamic picture, we explore the emergence of unreported magnetic modes induced by Dirac plasmon polaritons resulting from terahertz photon and Dirac electron interactions. We observe their profound impact on electric and magnetic transitions of quantum emitters near Bi2Se3 nanospheres, resulting in record - high Purcell factors. Our research highlights the rich optical response of Bi2Se3 nanospheres, involving contributions from both phonon polaritons and topologically protected surface states. Our findings confirm the emergence of topological optical modes in Bi2Se3 spherical TIs, positioning them as promising candidates for advancements in strong light-matter interactions in topological nanophotonics and THz technologies.
We employ a quantum mechanical model to describe nonclassical effects in the optical response of crystalline noble metal films, demonstrating that such effects can be contained in quantum surface-response functions known as Feibelman d-parameters. In particular, we extract d-parameters characterizing the surface response of (111) and (100) crystallographic facets of silver, gold, and copper, and apply them in simple optical response calculations to capture important features emerging due to electron spill-in/out, surface states, and the projected electronic gap emerging from corrugation of the confinement potential by stacked atomic planes.
We present a thorough theoretical study of the optical properties of periodic structures built of silver and silica
nanodisks in a sandwich-like configuration, by means of full electrodynamic calculations using the extended
layer-multiple-scattering method. The strong coupling of the metallic nanoparticles and the resulting plasmon
hybridization lead to collective electric and magnetic resonant modes, which can be tuned by changing the
structural parameters, such as nanoparticle size and lattice constant. We analyze the response of single- and
multi-layer architectures of ordered arrays of such nanosandwiches on a dielectric substrate to externally incident
light and evaluate the corresponding effective permittivity and permeability functions. Our results reveal the
existence of optical magnetism, with a strong negative effective permeability over a tunable spectral range at
near-infrared and visible frequencies. We introduce the complex photonic band structure as a tool in the study
of three-dimensional metamaterials and establish additional criteria for the validity of their effective-medium
description. Our work demonstrates the efficiency of the recently developed extended layer-multiple-scattering
method in the study of metamaterials of composite metal-dielectric particles of arbitrary shape.
Periodic nanostructures for plasmonic engineering, comprising one or two types of silica core - metallic shell spherical particles, are studied by means of full electrodynamic calculations using the layer-multiple-scattering method. The complex photonic band structure of such three-dimensional crystals is analyzed in conjunction with relevant transmission spectra of corresponding finite slabs and the physical origin of the different optical modes is elucidated, providing a consistent interpretation of the underlying physics. In the case of binary structures, collective plasmonic modes originating from the two building components coexist, leading to broadband absorption and a rich structure of resonances and hybridization gaps over an extended frequency range.
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