Conference Agenda

Monolayer transition metal dichalcogenides (TMDs) like WS2 exhibit strong exciton resonances in the visible spectral range that govern their optical response. The excitonic light-matter interaction in these 2D quantum materials is inherently strong and highly tunable, which can be leveraged to realize mutable flat optical elements as well as novel spin-valley coupled information carriers.

Here, I will showcase experimental realizations of coherent coupling to hybrid light-matter quasiparticles known as 2D exciton polaritons (2DEPs) in nanopatterned monolayers of WS2, allowing for enhanced and tunable photonic functionality given directly by the geometry of the monolayer itself. Using guided mode resonances in sub-wavelength gratings structured in mm-sized continuous WS2 monolayers, we can realize dynamic control of light scattered coherently off the hybrid light-matter state via electrical and/or thermal tuning. Further utilization of photonic metasurface concepts allows for angle-dependent amplitude switching of grating diffraction orders via perturbative approaches, leading to expected modulation depths exceeding 13dB stemming from an atomically thin optical element. This opens a path to full active control over the complex optical response in tailored atomically thin metasurfaces via exciton resonance tuning.

The study of Dirac plasmon polaritons (DPPs) in two-dimensional materials has raised considerable interest in the last years for the development of tunable optical devices, plasmonic sensors, ultrafast absorbers, modulators, and switches. In particular, topological insulators (TIs) represent an ideal material platform by virtue of the plasmon polaritons sustained by the Dirac carriers in their surface states. However, tracking DPP propagation at terahertz (THz) frequencies, with wavelength much smaller than that of the free-space photons, represents a challenging task. Herein, we trace the propagation of DPPs in TI-based coupled antennas. We show how Bi2Se3 rectangular nano-antennas effectively confine DPPs propagation to one dimension, enhancing their visibility despite intrinsic attenuation. Furthermore, plasmon dispersion and loss properties of coupled antenna resonators, patterned at varying lengths and distances are experimentally determined using holographic near-field nano-imaging at different THz frequencies. Our study evidences modifications on the DPP wavelength along the single nano-antenna ascribable to the cross-talk between neighbouring elements. The results provide insights into DPPs characteristics, paving the way for the design of novel topological devices and metasurfaces by leveraging their directional propagation capabilities.

Van der Waals (vdW) materials are ideal for nanoscale light-matter interactions. Here, we use quasi-bound states in the continuum (qBIC) to achieve high Q factor optical resonances in hBN and TMDC metasurfaces. In hBN metasurfaces, we achieve spectral tuning across the visible spectrum, enhance non-linear optical processes, and coupling of optically active defects. In WS2 metasurfaces, we observe strong anti-crossing between qBIC resonances and excitons, with Rabi splitting up to 116 meV. These results demonstrate the potential of vdW materials combined with qBIC for advanced nanophotonic platforms and room-temperature polaritonic devices.

In this work, we discuss the challenges associated with measuring and interpreting the vibrational properties of nanomaterials at mid- and far-infrared frequencies, where vibrational bands are often broad and overlapping. This issue is compounded by the complex interaction between infrared light and particulate samples, which depends on packing density and particle connectivity. Preliminary results concerning the far-infrared optical properties of Fe 3 O 4 nanoparticles have been obtained using the two most reliable methods (specular reflectance and attenuated total reflectance). These results are compared to one another and to their Raman counterparts. Finally, the influences of particle size and composition on the vibrational spectra are qualitatively discussed.