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The study of the highly tunable plasmonic spectral features has received growing interest in recent years because of broad range of potential applications in the next generation photonics technologies. Here, we developed a four-member nanoparticle cluster composed of gold nanodisks, where two of the nanodisks are connected by a metallodielectric bridge composed of Ge2Sb2Te5 and gold sections. We showed that the optothermal functionality of the Ge2Sb2Te5 allows for excitation of Fano resonances and charge transfer plasmons in a single system. This feature opens new paths for developing highly tunable nanophotonic devices.

Plasmonic waveguides are strategic compact structures consisting of nanoscale components and/or particles to carry the light. Here, by proposing a systematic and artificial configuration of fused nanoparticle assemblies, we develop an optothermally controllable plasmonic waveguide with high and tunable decay length for propagation of both single- and multimode waves. Using symmetric nanoplasmonic clusters based on phase-change material, here Ge2Sb 2Te5, allowed us to efficiently control the beam propagation length and quality at the global telecommunication bands (λ $\approx$ 850 nm and λ $\approx$ 1550 nm). Employing both finite-difference time-domain and finite element method as numerical tools, we accurately computed the critical components of the proposed multifunctional plasmonic light carrier. We believe that the tailored subwavelength optical waveguide paves new approaches to develop practical advanced next-generation nanophotonic technologies.

In this letter, we propose a terahertz (THz) plasmonic metamaterial based on planar metamolecule arrays with strong polarization sensitivity and large-modulation-depth for potential switching applications. Using both numerical and experimental studies, we analyzed the spectral features of the plasmonic unit cells. Employing bimetallic resonators, we showed that the proposed metamolecules can be efficiently tailored to support strong toroidal dipole resonant mode across the THz spectrum with high quality factor. The photo-induced toroidal moment with ultrasharp linewidth is used to design a polarization sensitive structure. This approach is the first utilization of toroidal metamaterials for switching applications, possessing strong potential to be used for advanced integrated photonic devices.

We numerically demonstrate high quality excitation, localization, and hybridization of plasmon resonant modes in an antisymmetric eight-member nanoshell oligomer (octamer) consisting of gold (Au) nanoshells deposited on a multilayer substrate composed of $\bm\beta$ -SiC/SiO2/Si layers. Using the geometrical tunability of nanoshells, we analyze excitation and interference of sub- and superradiant plasmon modes and present scattering cross-sectional spectra. It is shown that multilayer substrate plays a fundamental role in confinement of optical power in the nanoshell octamer, and results in the formation of a pronounced Fano minimum. A maximum value of ∼0.992 for the confinement factor is achieved in the proposed structure by optimizing the substrate thickness. To demonstrate the possibility of practical applications, we immerse the structure in liquids with different refractive indices, and observe how the Fano dip shifts. This method allows the calculation of figure of merit (FoM) which is plasmon resonance variations (Δ E eV) over the refractive perturbations ( n ) as 22.25 for the proposed nanocomplex. This study would make the utilization of compact multilayer configurations composed of nanoparticle aggregates possible to design high-precision, high-sensitivity (bio) chemical sensors.

Plasmonic nanoparticles in complex clusters and in specific molecular orientations are able to support strong plasmon and Fano resonances in their nanoscale geometries. In this paper, we examine the spectral response of a symmetric necklace shape nanostructure composed of Au nanodisk heptamers that are located in a close proximity to each other. Determining the appropriate geometrical parameters for the proposed necklace, we analyzed the effect of geometrical variations on the Fano resonance position and quality by calculating the scattering cross-sectional profile, numerically. Considering the strong localization of surface plasmon resonances (LSPR) in the heptamer clusters, the LSPR sensitivity for the studied necklace has been determined. Moreover, we evaluated the performance of the structure for different medium conditions by plotting corresponding figure of merit (FoM). To this end, we measured the plasmon resonance energy differences (Δ E eV) over the refractive index (n) alterations, we quantified the corresponding FoM for the final necklace as 13.7, which can be utilized in designing precise and highly sensitive sensors. Ultimately, we proved that highly complex structures composed of metal nanoparticles clusters yield high sensitivity to the environmental perturbations.