Toward Cavity Quantum Electrodynamics with Hybrid Photon Gap-Plasmon States.

Combining localized surface plasmons (LSPs) and diffractive surface waves (DSWs) in metallic nanoparticle gratings leads to the emergence of collective hybrid plasmonic-photonic modes known as surface lattice resonances (SLRs). These show reduced losses and therefore a higher Q factor with respect to pure LSPs, at the price of larger volumes. Thus, they can constitute a flexible and efficient platform for light-matter interaction. However, it remains an open question if there is, in terms of the Q/V ratio, a sizable gain with respect to the uncoupled LSPs or DSWs. This is a fundamental point to shed light upon if such modes want to be exploited, for instance, for cavity quantum electrodynamic effects. Here, using aluminum nanoparticle square gratings with unit cells consisting of narrow-gap disk dimers-a geometry featuring a very small modal volume-we demonstrate that an enhancement of the Q/V ratio with respect to the pure LSP and DSW is obtained for SLRs with a well-defined degree of plasmon hybridization. Simultaneously, we report a 5× increase of the Q/V ratio for the gap-coupled LSP with respect to that of the single nanoparticle. These outcomes are experimentally probed against the Rabi splitting, resulting from the coupling between the SLR and a J-aggregated molecular dye, showing an increase of 80% with respect to the DSW-like SLR sustained by the disk LSP of the dimer. The results of this work open the way toward more efficient applications for the exploitation of excitonic nonlinearities in hybrid plasmonic platforms.

Broadband absorption enhancement in plasmonic nanoshells-based ultrathin microcrystalline-Si solar cells.

With the objective to conceive a plasmonic solar cell with enhanced photocurrent, we investigate the role of plasmonic nanoshells, embedded within a ultrathin microcrystalline silicon solar cell, in enhancing broadband light trapping capability of the cell and, at the same time, to reduce the parasitic loss. The thickness of the considered microcrystalline silicon (µc-Si) layer is only ~1/6 of conventional µc-Si based solar cells while the plasmonic nanoshells are formed by a combination of silica and gold, respectively core and shell. We analyze the cell optical response by varying both the geometrical and optical parameters of the overall device. In particular, the nanoshells core radius and metal thickness, the periodicity, the incident angle of the solar radiation and its wavelength are varied in the widest meaningful ranges. We further explain the reason for the absorption enhancement by calculating the electric field distribution associated to resonances of the device. We argue that both Fabry-Pérot-like and localized plasmon modes play an important role in this regard.