Conference Agenda

Optical metasurfaces have emerged as powerful, flat photonic elements capable of tailoring light at the sub-wavelength scale. In particular, quasi-bound states in the continuum (qBIC) metasurfaces enable the creation of high quality (Q) factor resonances in ultrathin nanophotonic structures, offering a promising route to enhanced light–matter interactions. In this talk, I will present our recent advances in integrating van der Waals (vdW) materials with qBIC metasurfaces to realize robust exciton–polaritons. We first demonstrate self-hybridized polaritons in patterned WS2 metasurfaces, where the interplay between excitons and engineered photonic modes leads to Rabi splitting above 100 meV, in ambient conditions. Furthermore, we explore hBN-based dielectric metasurfaces supporting ultra-high Q resonances, with values exceeding 2000 across the visible range. Finally, by vertically stacking hBN with WS2 monolayer semiconductors, we realize room-temperature exciton-polaritons in vdW heterostructures, with nonlinearities three orders of magnitude larger than previous approaches. Our results pave the way for compact polaritonic devices with enhanced nonlinear responses, offering new avenues for low-threshold condensation and coherent photonic circuits operating at room temperature.

We present a hydrodynamic model based on Madelung's approach to describe the plasmonic properties of anisotropic materials. In this modelling, nonlocal effects arise from the Bohm potential and Thomas-Fermi quantum pressure.

We find exact formulas for the dispersion relation of magnetoplasmons and the optical conductivity, considering nonlocal effects. We apply them to monolayer phosphorene, a two-dimensional material known for its anisotropic properties. The plasmon dispersion of our model matches well with results from first-principles calculations.

Our findings show that including nonlocal and quantum effects explains why phosphorene does not support hyperbolic surface plasmon polaritons. This highlights the importance of going beyond simple models when studying materials that can support tightly confined plasmon-polaritons.

We explore the nonlinear optical properties of graphene and phosphorene nanoribbons using ab initio modeling and self-consistent perturbation theory. These two-dimensional materials exhibit significant potential for frequency conversion, optical modulation, and ultrafast signal processing due to their inherent nonlinear responses and tunable plasmonic characteristics. Our investigations reveal that graphene nanoribbons (GNRs) photoexcited by intense ultrashort optical pulses exhibit strong transient nonlinear optical responses driven by thermally activated plasmons, demonstrating a robust, non-invasive method for achieving tunable nonlinear effects without the need for excessive charge carrier doping. In a parallel study, we investigate enhanced nonlinear interactions in nanoribbon heterostructures, where the synergetic combination of tunable plasmons and anharmonic electron dispersion in graphene and phosphorene offers unique opportunities for device engineering.

Heavily doped semiconductors have emerged as an enabling platform for mid-infrared photonics, leveraging free electrons to achieve strong and tunable nonlocal-nonlinear light-matter interactions. In this talk, we will discuss recent theoretical and experimental studies on third harmonic generation and Kerr nonlinearity in heavily doped semiconductors, in which hydrodynamic contributions dominate.