The ability of a naturally hyperbolic van der Waals material α-MoO3 to sustain hyperbolic phonon-polaritons allows extreme localization of the mid-infrared electromagnetic field on a subwavelength scale. We propose periodic nanohole arrays in exfoliated α-MoO3 nanoflakes to tune the wavelength of phonon-polariton resonances. We report on the optical properties of α-MoO3 nanohole arrays and their dependence on their geometry. Results have been confirmed using the finite-difference time-domain simulations and near-field mapping of phonon-polaritonic modes. We observe an unusual behavior of the transmission spectra in the fundamental absorption band, where the phononic absorption can be almost entirely alleviated.
We discuss our recent results in nanophotonic properties of engineered naturally hyperbolic van der Waals materials. We thermomechanically control thin MoO3 flakes to tune their crystallographic and phonon-polaritonic properties. We show induction of an irreversible strain of up to -2.4% and tuning of the phonon-polaritonic dispersion relationship by more than 10%. By patterning a nanohole array in the exfoliated flakes, resonant phonon-polaritonic excitations result in more than an order of magnitude in mid-infrared field enhancement, resulting in a strong experimentally verified near-field response and enhancement of nonlinear optical properties.
Due to their unusual features in condensed matter physics and their applicability in optical and optoelectronic applications, three-dimensional Dirac semimetals (3D DSMs) have garnered substantial interest in recent years. In contrast to monolayer graphene, 3D DSM exhibits linear band dispersion despite its macroscopic thickness. Therefore, being a bulk material, it is easy to make nanostructures with 3D DSM, just as one normally does with metals such as gold and silver. Among 3D DSMs, cadmium arsenide (Cd3As2) is quite famous and considered an excellent 3D DSM due to its chemical stability in air and extraordinary optical response. In this review, advances in 3D DSM Cd3As2 fabrication techniques and recent progress in the photonics of 3D DSM Cd3As2 are given and briefly reviewed. Various photonic features, including linear and nonlinear plasmonics, optical absorption, optical harmonic generation, and ultrafast dynamics, have been explored in detail. It is expected that Cd3As2 would share an excellent tunable photonic response like graphene. We envision that this article may serve as a concise overview of the recent progress of photonics in 3D DSM Cd3As2 and provides a compact reference for young researchers.
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