Resonances in doubly anisotropic, high-index nanoplatelets

High-refractive-index nanoplatelets with intrinsic out-of-plane anisotropy and substantial birefringence hold promise for revolutionizing optical components. Traditional materials, such as inorganic solids and liquid crystals, have limited birefringence, hindering device efficiency. Transition metal dichalcogenides like molybdenum disulfide (MoS2), have emerged as potential candidate. Their layered van der Waals structure naturally results in high intrinsic birefringence, particularly in the near-infrared spectrum. The presence of strong excitons endows MoS2 with a high in-plane refractive index above 4.5 and makes it possible to have high out-of-plane index contrast. A high refractive index also enables the existence Mie-type resonances in MoS2 nanostructures for enhancing and controlling light-matter interaction.
  Here, we study the optical resonances sustained by nanoplatelets with high refractive index and optical anisotropy. Nanoplatelets have both geometrical and refractive index anisotropies, sustaining electric and magnetic multipolar resonances. We investigate the distinct impact of changes in height and birefringence on the tunability of  different resonances and use a multipolar analysis to understand the influence of anisotropy on each resonance. We find magnetic dipole are particularly sensitive to anisotropy changing. Due to their double anisotropy, nanoplatelets also show a strong dependence of their optical response on plane wave illuminating direction. We relate the nature of the resonances under illumination with the same electric or magnetic field polarization and different directions of incidence and consider the impact of retardation effects. Finally, we show that nanoplatelets can also control the polarization and directionality of dipolar sources such as fluorescent molecules due to the preferential excitation of in-plane resonances. Overall, these high-refractive-index nanoplatelets, with their unique combination of properties, have the potential to enhance and direct light scattering and emission. This breakthrough holds significant promise for applications in light-emitting devices and random lasers, potentially reshaping the landscape of optical technology and advancing its efficiency and versatility.