Exciton Polaritons in Emergent Two-Dimensional Semiconductors

Enhanced Free-Electron-Photon Interactions at the Topological Transition in van der Waals Heterostructures

Heterostructures composed of graphene and molybdenum trioxide (MoO3) can support in-plane hybrid polaritons in the infrared. The isofrequency contour for these subwavelength polaritons can exhibit a quasi-flat region when the topological transition occurs as the doping level of graphene is tuned. Such a topological transition can be useful for optical sensing and imaging at nanoscale. Here, by analyzing electron energy-loss spectroscopy (EELS), we theoretically demonstrate that free-electron-photon interactions in the heterostructure can be enhanced due to this quasi-flat region. Moreover, the free-electron-photon interaction is sensitive to the electron trajectory and is robust against certain types of defects in the structure. Furthermore, we show that the free-electron-photon interaction can undergo an ultrafast subpicosecond modulation by optical pumping and heating of graphene. Our findings may pave the way toward dynamical electron beam shaping, free-electron-based quantum light sources, and quantum sensing.

Room-Temperature Exciton Polaritons in a Monolayer Molecular Crystal

Strong coupling between excitons and photons in optical microcavities leads to the formation of exciton polaritons, which maintain both the coherence of light and the interaction of matter. Recently, atomically thin monolayer semiconductors with a large exciton oscillator strength and high exciton binding energy have been widely used for realizing room-temperature exciton polaritons. Here, we demonstrated room-temperature exciton polaritons with a monolayer molecular crystal. The molecular monolayers behave as J-aggregates with comparable oscillator strength and narrow line width as inorganic monolayers, enabling exciton-photon strong coupling at the monolayer limit. Moreover, the coupling strength can be tuned systematically via engineering the in-plane polarization or by using a vertical stack of multiple molecular monolayers. Our research provides a new material platform for realizing strong light-matter interactions inside optical microcavities at room temperature and may motivate the development of molecular-crystal-based exciton-polaritonic devices with novel functions and new possibilities.

Room temperature polaritonic soft-spin XY Hamiltonian in organic-inorganic halide perovskites

Exciton-polariton condensates, due to their nonlinear and coherent characteristics, have been employed to construct spin Hamiltonian lattices for potentially studying spin glass, critical dephasing, and even solving optimization problems. Here, we report the room-temperature polariton condensation and polaritonic soft-spin XY Hamiltonian lattices in an organic-inorganic halide perovskite microcavity. This is achieved through the direct integration of high-quality single-crystal samples within the cavity. The ferromagnetic and antiferromagnetic couplings in both one- and two-dimensional condensate lattices have been observed clearly. Our work shows a nonlinear organic-inorganic hybrid perovskite platform for future investigations as polariton simulators.

Quasi-bound states in the continuum for electromagnetic induced transparency and strong excitonic coupling

Advancing on previous reports, we utilize quasi-bound states in the continuum (q-BICs) supported by a metasurface of TiO2 meta-atoms with broken inversion symmetry on an SiO2 substrate, for two possible applications. Firstly, we demonstrate that by tuning the metasurface's asymmetric parameter, a spectral overlap between a broad q-BIC and a narrow magnetic dipole resonance is achieved, yielding an electromagnetic induced transparency analogue with a 50 μs group delay. Secondly, we have found that, due to the strong coupling between the q-BIC and WS2 exciton at room temperature and normal incidence, by integrating a single layer of WS2 to the metasurface, a 37.9 meV Rabi splitting in the absorptance spectrum with 50% absorption efficiency is obtained. These findings promise feasible two-port devices for visible range slow-light characteristics or nanoscale excitonic coupling.

Cutting-Edge Research in Nanoscience and Nanotechnology: Celebrating the 130th Anniversary of Wuhan University

Thanks to the fast-paced progress of microscopic theories and nanotechnologies, a tremendous world of fundamental science and applications has opened up at the nanoscale. Ranging from quantum physics to chemical and biological mechanisms and from device functionality to materials engineering, nanoresearch has become an essential part of various fields. As one of the top universities in China, Wuhan University (WHU) aims to promote cutting-edge nanoresearch in multiple disciplines by leveraging comprehensive academic programs established throughout 130 years of history. As visible in prestigious scientific journals such as ACS Nano, WHU has made impactful advancements in various frontiers, including nanophotonics, functional nanomaterials and devices, biomedical nanomaterials, nanochemistry, and environmental science. In light of these contributions, WHU will be committed to serving talents and scientists wholeheartedly, fully supporting international collaborations and continuously driving innovative research.