Transition metal dichalcogenide nanodisks as high-index dielectric Mie nanoresonators (1812.04076v1)

Abstract: Monolayer transition metal dichalcogenides (TMDCs) have recently been proposed as a unique excitonic platform for advanced optical and electronic functionalities. However, in spite of intense research efforts, it has been largely overlooked that, in addition to displaying rich exciton physics, TMDCs also possess a very high refractive index. This opens a possibility to utilize these materials for constructing resonant nanoantennas based on subwavelength geometrical modes. Here we show that nanodisks fabricated from exfoliated multilayer WS$_2$ support distinct Mie resonances and so-called anapole states that can be easily tuned in wavelength over the visible and near-infrared spectral range by varying the nanodisks' size and aspect ratio. We argue that the TMDC material anisotropy and the presence of excitons substantially enrich nanophotonics by complementing traditional approaches based on plasmonics and well-known high-index materials such as silicon. As a proof-of-concept, we demonstrate a novel regime of light-matter interaction, anapole-exciton polaritons, which we realize within a single WS$_2$ nanodisk. Our results thus suggest that nanopatterned TMDCs are promising materials for high-index nanophotonics applications with enriched functionalities and superior prospects.

• The paper introduces WS2 nanodisks as high-index dielectric Mie nanoresonators, enabling tunable resonances across the visible to near-infrared spectrum.
• The paper demonstrates strong exciton–Mie coupling, evidenced by spectral anti-crossing and a vacuum Rabi splitting of approximately 190 meV.
• The paper highlights the potential for advanced optical applications, including enhanced photodetection, light harvesting, and nonlinear optics.

High-Index Dielectric Nanoresonators: Transition Metal Dichalcogenide Nanodisks

The paper under examination investigates the utilization of transition metal dichalcogenides (TMDCs), specifically WS$_2$ nanodisks, as high-index dielectric (HID) Mie nanoresonators. These materials have been identified not only for their prominent exciton properties but also for their considerable refractive indices, which present exciting opportunities in the field of dielectric nanophotonics. The primary focus is on the exploration of these nanodisks as a new platform for high-index nanophotonics, complementing existing structures made from materials such as silicon.

Key Findings and Experimental Overview

The paper presents robust experimental evidence demonstrating that WS$_2$ nanodisks support distinct Mie resonances and anapole states, which are tunable across the visible to near-infrared spectral range by modulating the physical dimensions of the nanodisks. The authors further introduce the concept of anapole-exciton polaritons, marking the intersection of nanophotonics with quantum exciton dynamics within these nanodisks.

Strong Numerical Results:

• The analysis of the TMDCs reveals a high refractive index (n > 4) in the visible spectrum, which surpasses many traditionally used HID materials like silicon.
• The paper demonstrates a strong coupling regime, confirmed experimentally through observed spectral anti-crossing, with a vacuum Rabi splitting of approximately 190 meV.

Implications and Theoretical Perspectives

The findings have profound implications for the development of advanced optical devices. The high dielectric constants facilitate novel light-matter interaction regimes, offering potential for enhanced applications in light harvesting, photodetection, and nonlinear optics. The strong coupling observed between Mie resonances and excitons within these nanodisks suggests exciting prospects for developing compact photonic systems capable of supporting polaritonic modes.

Future Directions in AI and Nanophotonics

The paper opens several avenues for future research in nanophotonics, especially in the field of AI-driven design and optimization of nanostructures. The unique optical properties of TMDCs, combined with their high crystalline quality and compatibility with other materials, offer a promising platform for the application of machine learning algorithms to optimize and discover new functionalities in nanophotonic devices. Machine learning techniques could be harnessed to predict and enhance light-matter interactions within such nanoscale systems, potentially leading to innovative designs for data processing and energy-efficient computation.

Conclusion

In conclusion, this paper expands the library of high-index dielectric materials applicable to nanophotonics by effectively utilizing the unique optical properties of WS$_2$ nanodisks. By demonstrating experimentally the presence of anapole states and strong coupling effects, the authors have laid the groundwork for future exploration of TMDCs in advanced optical applications. The observed phenomena not only deepen the understanding of light-matter interactions but also suggest exciting potential in integrating these nanodisks into practical photonic devices. The research thus represents a significant step forward in the ongoing exploration of novel HID materials and their possibilities within the field of nanotechnology.