We present an interferometrically resolved study of the amplitude and phase response of plasmon array etalons composed of a reflective surface with a metasurface of resonant plasmonic dipole antennas in front of it. Above a minimum antenna oscillator strength (set by antenna size and density), such structures show conditions of perfect absorption. In the parameter space spanned by frequency and etalon spacing, these singular points unavoidably come in pairs and are associated with a phase singularity. The topologically oppositely charged point pairs occur around the geometric Fabry−Peŕot condition. We elucidate the origin of these singularities and their continuous evolution with oscillator strength in the 2D plane spanned by optical frequency and mirror-antenna spacing. Our findings extend the understanding of Salisbury screens and of "pixels" in reflective metasurfaces for full control of amplitude and phase. Finally, our data demonstrates the limits of transfer-matrix approaches to predicting the response of arbitrary stacks of metasurfaces and dielectric layers.

Semiconductor nanocrystals, or quantum dots (QDs), simultaneously benefit from inexpensive low-temperature solution processing and exciting photophysics, making them the ideal candidates for next-generation solar cells and photodetectors. While the working principles of these devices rely on light absorption, QDs intrinsically belong to the Rayleigh regime and display optical behavior limited to electric dipole resonances, resulting in low absorption efficiencies. Increasing the absorption efficiency of QDs, together with their electronic and excitonic coupling to enhance charge carrier mobility, is therefore of critical importance to enable practical applications. Here, we demonstrate a general and scalable approach to increase both light absorption and excitonic coupling of QDs by fabricating hierarchical metamaterials. We assemble QDs into crystalline supraparticles using an emulsion template and demonstrate that these colloidal supercrystals (SCs) exhibit extended resonant optical behavior resulting in an enhancement in absorption efficiency in the visible range of more than 2 orders of magnitude with respect to the case of dispersed QDs. This successful light trapping strategy is complemented by the enhanced excitonic coupling observed in ligand-exchanged SCs, experimentally demonstrated through ultrafast transient absorption spectroscopy and leading to the formation of a free biexciton system on sub-picosecond time scales. These results introduce a colloidal metamaterial designed by self-assembly from the bottom up, simultaneously featuring a combination of nanoscale and mesoscale properties leading to simultaneous photonic and excitonic coupling, therefore presenting the nanocrystal analogue of supramolecular structures.

Monocrystalline materials are essential for optoelectronic devices such as solar cells, LEDs, lasers, and transistors to reach the highest performance. Advances in synthetic chemistry now allow for high quality monocrystalline nanomaterials to be grown at low temperature in solution for many materials; however, the realization of extended structures with control over the final 3D geometry still remains elusive. Here, a new paradigm is presented, which relies on epitaxy between monocrystalline nanocube building blocks. The nanocubes are assembled in a predefined pattern and then epitaxially connected at the atomic level by chemical growth in solution, to form monocrystalline nanopatterns on arbitrary substrates. As a first demonstration, it is shown that monocrystalline silver structures obtained with such a process have optical properties and conductivity comparable to single-crystalline silver. This flexible multiscale process may ultimately enable the implementation of monocrystalline materials in optoelectronic devices, raising performance to the ultimate limit.

AbstractIn this work we present a simple transfer-matrix based modeling tool for arbitrarily layered stacks of resonant plasmonic metasurfaces interspersed with dielectric and metallic multilayers. We present the application of this model by analyzing three seminal problems in nanophotonics. These are the scenario of perfect absorption in plasmonic Salisbury screens, strong coupling of microcavity resonances with the resonance of plasmon nano-antenna metasurfaces, and the hybridization of cavities, excitons and metasurface resonances.

We have measured the optical signatures of strong coupling between the resonance of etalons and plasmon antenna arrays in transmission and polarization. Planar etalons in the middle of which a plasmon antenna array is placed show anticrossings in transmission between the etalon resonances and plasmon antenna resonance, which we map as a function of frequency, etalon opening and oscillator strengh. We argue that the proper interpretation of strong coupling and the magnitude of the Rabi splitting requires a "metasurface-in-the-middle" cavity model and is distinct from strong coupling between a cavity and a dispersive material. Furthermore, we quantitatively connect the Rabi splitting to the electrostatic antenna polarizability, that is, the polarizability in the absence of radiative damping corrections. Finally, we demonstrate that the strong coupling brings very strong polarization conversion effects, as the hybrid modes provide for a strong retardance that can be leveraged for linear birefringence and dichroism.