arXiv subjects

Yuebing Zheng

Publications and source records attributed to Yuebing Zheng.

14 recordsLinked to original sources

arXiv2026

Electrical Probing of Dark Excitons through Microwave Permittivity

Excitons in atomically thin semiconductors are almost always probed through their optical signatures, because the short lifetimes of these transient quasiparticles are generally assumed to preclude electrical detection. Here we show that photoexcited excitons in monolayer tungsten disulfide produce a large, optically tunable permittivity at gigahertz frequencies, and that the effect provides a contact-free electrical route to imaging dark excitons at the nanoscale. Using laser-illuminated microwave impedance microscopy, we find that high-purity encapsulated flakes exhibit a purely dielectric response resonant with the exciton spectrum, whereas defect-rich samples are governed by conventional photoconductivity. Spatial mapping of diffusion and sublinear power dependence identify long-lived dark excitons as the dominant contributors, and first-principles modelling of exciton polarizability reproduces the measured susceptibility. Our results establish excitons as optically tunable dielectric elements and introduce microwave microscopy as a direct electrical probe of dark-exciton transport with sub-100 nm resolution.

cond-mat.mes-hall↗

arXiv2025

Multimodal Guided Surface Lattice Resonances in Index-Discontinuous Environments

Surface lattice resonances (SLRs) in metasurfaces have become a transformative platform for subwavelength optical devices, leveraging their high quality (Q)-factors, pronounced local field enhancement, and extensive long-range interactions. However, current high-Q SLR implementations are fundamentally limited by their dependence on homogeneous dielectric environments. This restriction significantly hinders their applicability in emerging fields such as molecular sensing, where operation in heterogeneous dielectric media (e.g., interfaces with an aqueous or air cladding) is often indispensable. To overcome this limitation, we introduce guided surface lattice resonances (gSLRs) by integrating nanoparticle arrays within slab waveguides. This configuration facilitates efficient coupling between scattered light and Bloch modes, thereby enabling high-Q multimodal resonances even in index-discontinuous environments. Experimental validation under incoherent illumination demonstrates a Q-factor of 1489 in an index-mismatched surrounding. Furthermore, the coupling strength and resonance intensity of these multimodal gSLRs can be continuously modulated by adjusting the vertical displacement of the nanoparticle arrays within the slab layers. To augment the sensitivity to local dielectric variations, we investigate gSLRs in metasurfaces integrated with metallic substrates, demonstrating suitability for biomolecule detection. A mathematical sensing model, incorporating biochemical reaction kinetics and optical responses, is established by representing adsorbed molecules as a uniform dielectric layer and validated through bovine serum albumin (BSA) sensing experiments. This work not only advances the fundamental understanding of resonance engineering in complex media but also facilitates the development of ultrathin, ultra-compact nano-optical and optoelectronic devices.

physics.optics↗

arXiv2024

Independently Tunable Flat Bands and Correlations in a Graphene Double Moiré System

We report on a double moiré system consisting of four graphene layers, where the top and bottom pairs form small-twist-angle bilayer graphene, and the middle interface has a large rotational mismatch. This system shows clear signatures of two sets of spatially separated flat bands associated with the top and bottom twisted bilayer graphene (TBG) subsystems, each independently tunable. Thermodynamic analysis reveals weak correlations between layers that allow the chemical potential to be measured as a function of carrier density for each constituent TBG. We find that correlated insulating states at integer number of electrons per moiré unit cell are most robust near magic angle, whereas gapped states at neutrality are more robust at larger twist angles.

cond-mat.mes-hall↗

arXiv2024

Million-Q Free Space Meta-Optical Resonator at Visible Wavelengths

High-quality (Q)-factor optical resonators with extreme temporal coherence are of both technological and fundamental importance in optical metrology, continuous-wave lasing, and semiconductor quantum optics. Despite extensive efforts in designing high-Q resonators across different spectral regimes, the experimental realization of very large Q-factors at visible wavelengths remains challenging due to the small feature size that is sensitive to fabrication imperfections, and thus is typically implemented in integrated photonics. In the pursuit of free-space optics with the benefits of large space-bandwidth product and massive parallel operations, here we design and fabricate a visible-wavelength etch-free metasurface with minimized fabrication defects and experimentally demonstrate a million-scale ultrahigh-Q resonance. A new laser-scanning momentum-space-resolved spectroscopy technique with extremely high spectral and angular resolution is developed to characterize the record-high Q-factor as well as the dispersion of the million-Q resonance in free space. By integrating monolayer WSe2 into our ultrahigh-Q meta-resonator, we further demonstrate laser-like highly unidirectional and narrow-linewidth exciton emission, albeit without any operating power density threshold. Under continuous-wave laser pumping, we observe pump-power-dependent linewidth narrowing at room temperature, indicating the potential of our meta-optics platform in controlling coherent quantum light-sources. Our result also holds great promise for applications like optical sensing, spectral filtering, and few-photon nonlinear optics.

physics.optics↗

arXiv2024

Manipulating Fano coupling in an opto-thermoelectric field

Fano resonances in photonics arise from the coupling and interference between two resonant modes in structures with broken symmetry. They feature an uneven and narrow and tunable lineshape, and are ideally suited for optical spectroscopy. Many Fano resonance structures have been suggested in nanophotonics over the last ten years, but reconfigurability and tailored design remain challenging. Herein, we propose an all-optical pick-and-place approach aimed at assemble Fano metamolecules of various geometries and compositions in a reconfigurable manner. We study their coupling behavior by in-situ dark-field scattering spectroscopy. Driven by a light-directed opto-thermoelectric field, silicon nanoparticles with high quality-factor Mie resonances (discrete states) and low-loss BaTiO3 nanoparticles (continuum states) are assembled into all-dielectric heterodimers, where distinct Fano resonances are observed. The Fano parameter can be adjusted by changing the resonant frequency of the discrete states or the light polarization. We also show tunable coupling strength and multiple Fano resonances by altering the number of continuum states and discrete states in dielectric heterooligomers. Our work offers a general design rule for Fano resonance and an all-optical platform for controlling Fano coupling on demand.

physics.optics↗

arXiv2023

Light-driven C-H bond activation mediated by 2D transition metal dichalcogenides

C-H bond activation enables the facile synthesis of new chemicals. While C-H activation in short-chain alkanes has been widely investigated, it remains largely unexplored for long-chain organic molecules. Here, we report light-driven C-H activation in complex organic materials mediated by 2D transition metal dichalcogenides (TMDCs) and the resultant solid-state synthesis of luminescent carbon dots in a spatially-resolved fashion. We unravel the efficient H adsorption and a lowered energy barrier of C-C coupling mediated by 2D TMDCs to promote C-H activation. Our results shed light on 2D materials for C-H activation in organic compounds for applications in organic chemistry, environmental remediation, and photonic materials.

cond-mat.mtrl-sci↗

arXiv2023

Tuning Multipolar Mie Scattering of Particles on a Dielectric-Covered Mirror

Optically resonant particles are key building blocks of many nanophotonic devices such as optical antennas and metasurfaces. Because the functionalities of such devices are largely determined by the optical properties of individual resonators, extending the attainable responses from a given particle is highly desirable. Practically, this is usually achieved by introducing an asymmetric dielectric environment. However, commonly used simple substrates have limited influences on the optical properties of the particles atop. Here, we show that the multipolar scattering of silicon microspheres can be effectively modified by placing the particles on a dielectric-covered mirror, which tunes the coupling between the Mie resonances of microspheres and the standing waves and waveguide modes in the dielectric spacer. This tunability allows selective excitation, enhancement, and suppression of the multipolar resonances and enables scattering at extended wavelengths, providing new opportunities in controlling light-matter interactions for various applications. We further demonstrate with experiments the detection of molecular fingerprints by single-particle mid-infrared spectroscopy, and, with simulations strong optical repulsive forces that could elevate the particles from a substrate.

physics.optics↗

arXiv2023

Optothermal rotation of micro-/nano-objects in liquids

Controllable rotation of micro-/nano-objects provides tremendous opportunities for cellular biology, three-dimensional (3D) imaging, and micro/nanorobotics. Among different rotation techniques, optical rotation is particularly attractive due to its contactless and fuel-free operation. However, optical rotation precision is typically impaired by the intrinsic optical heating of the target objects. Optothermal rotation, which harnesses light-modulated thermal effects, features simpler optics, lower operational power, and higher applicability to various objects. In this Feature Article, we discuss the recent progress of optothermal rotation with a focus on work from our research group. We categorize the various rotation techniques based on distinct physical mechanisms, including thermophoresis, thermoelectricity, thermo-electrokinetics, thermo-osmosis, thermal convection, and thermo-capillarity. Benefiting from the different rotation modes (i.e., in-plane and out-of-plane rotation), diverse applications in single-cell mechanics, 3D bio-imaging, and micro/nanomotors are demonstrated. We conclude the article with our perspectives on the operating guidelines, existing challenges, and future directions of optothermal rotation.

physics.optics↗

arXiv2020

Directivity modulation of exciton emission using single dielectric nanospheres

Coupling emitters with nanoresonators is an effective strategy to control light emission at the subwavelength scale with high efficiency. Low-loss dielectric nanoantennas hold particular promise for this purpose, owing to their strong Mie resonances. Herein, we explore a highly miniaturized platform for the control of emission based on individual subwavelength Si nanospheres (SiNSs) to modulate the directional excitation and exciton emission of two-dimensional transition metal dichalcogenides (2D TMDs). A modified Mie theory for dipole-sphere hybrid systems is derived to instruct the optimal design for desirable modulation performance. Controllable forward-to-backward intensity ratios are experimentally validated in 532 nm laser excitation and 635 nm exciton emission from a monolayer WS2. Versatile light emission control along all device orientations is achieved for different emitters and excitation wavelengths, benefiting from the facile size control and isotropic shape of SiNSs. Simultaneous modulation of excitation and emission via a single SiNS at visible wavelengths significantly improves the efficiency and directivity of TMD exciton emission and leads to the potential of multifunctional integrated photonics. Overall, our work opens promising opportunities for nanophotonics and polaritonic systems, enabling efficient manipulation, enhancement and reconfigurability of light-matter interactions.

physics.optics↗

arXiv2019

Suppressing Material Loss for Functional Nanophotonics Using Bandgap Engineering

All-dielectric nanoantennas have recently opened exciting opportunities for functional nanophotonics, owing to their strong optical resonances along with low material loss in the near-infrared range. Pushing these concepts to the visible range is hindered by a larger absorption coefficient of Si and other high-index semiconductors, thus encouraging the search for alternative dielectrics for nanophotonics. In this paper, we employ bandgap engineering to synthesize hydrogenated amorphous Si nanoparticles (a-Si:H NPs) offering ideal features for functional nanophotonics. We observe significant material loss suppression in a-Si:H NPs in the visible range caused by hydrogenation-induced bandgap renormalization, producing resonant modes in single a-Si:H NPs with Q factors up to ~100, in the visible and near-IR range for the first time. In order to demonstrate light-matter interaction enhancement, we realize highly tunable all-dielectric nanoantennas coupling them to photochromic spiropyran (SP) molecules. We show ~70% reversible all-optical tuning of light scattering at the high-Q resonant mode, along with minor tunability when out of resonance. This remarkable all-optical tuning effect is achieved under a low incident light intensity ~3.8 W/cm2 for UV light and ~1.1*10^2 W/cm2 for green light.

physics.optics↗

arXiv2019

All-optical reconfigurable chiral meta-molecules

Chirality is a ubiquitous phenomenon in the natural world. Many biomolecules without inversion symmetry such as amino acids and sugars are chiral molecules. Measuring and controlling molecular chirality at a high precision down to the atomic scale are highly desired in physics, chemistry, biology, and medicine, however, have remained challenging. Herein, we achieve all-optical reconfigurable chiral meta-molecules experimentally using metallic and dielectric colloidal particles as artificial atoms or building blocks to serve at least two purposes. One is that the on-demand meta-molecules with strongly enhanced optical chirality are well-suited as substrates for surface-enhanced chiroptical spectroscopy of chiral molecules and as active components in optofluidic and nanophotonic devices. The other is that the bottom-up-assembled colloidal meta-molecules provide microscopic models to better understand the origin of chirality in the actual atomic and molecular systems. Keywords: opto-thermoelectric tweezers; optical chirality; metamolecules; bottom-up assembly

physics.optics↗

arXiv2019

Intelligent Nanophotonics: Merging Photonics and Artificial Intelligence at the Nanoscale

Nanophotonics has been an active research field over the past two decades, triggered by the rising interests in exploring new physics and technologies with light at the nanoscale. As the demands of performance and integration level keep increasing, the design and optimization of nanophotonic devices become computationally expensive and time-inefficient. Advanced computational methods and artificial intelligence, especially its subfield of machine learning, have led to revolutionary development in many applications, such as web searches, computer vision, and speech/image recognition. The complex models and algorithms help to exploit the enormous parameter space in a highly efficient way. In this review, we summarize the recent advances on the emerging field where nanophotonics and machine learning blend. We provide an overview of different computational methods, with the focus on deep learning, for the nanophotonic inverse design. The implementation of deep neural networks with photonic platforms is also discussed. This review aims at sketching an illustration of the nanophotonic design with machine learning and giving a perspective on the future tasks.

physics.optics↗

arXiv2019

Dark-Exciton-Mediated Fano Resonance from a Single Gold Nanostructure Deposited on Monolayer WS2 at Room Temperature

Strong spatial confinement and highly reduced dielectric screening provide monolayer transition metal dichalcogenides (TMDCs) with strong many-body effects, thereby possessing optically forbidden excitonic states (i.e., dark excitons) at room temperature. Herein, we explore the interaction of surface plasmons with dark excitons in hybrid systems consisting of stacked gold nanotriangles (AuNTs) and monolayer WS2. We observe a narrow Fano resonance when the hybrid system is surrounded by water, and we attribute the narrowing of the spectral Fano linewidth to the plasmon-enhanced decay of dark K-K excitons. Our results reveal that dark excitons in monolayer WS2 can strongly modify Fano resonances in hybrid plasmon-exciton systems and can be harnessed for novel optical sensors and active nanophotonic devices.

physics.optics↗

arXiv2017

Tunable Resonance Coupling in Single Si Nanoparticle-Monolayer WS2 Structures

Two-dimensional semiconducting transition metal dichalcogenides (TMDCs) are extremely attractive materials for optoelectronic applications in the visible and near-IR range. Here, we address for the first time to the best of our knowledge the issue of resonance coupling in hybrid exciton-polariton structures based on single Si nanoparticles coupled to monolayer WS2. We predict a transition from weak to strong coupling regime , with a Rabi splitting energy exceeding 200 meV for a Si nanoparticle covered by monolayer WS 2 at the magnetic optical Mie resonance. This large transition is achieved due to the symmetry of magnetic dipole Mie mode and by changing the surrounding dielectric material from air to water. The prediction is based on the experimental estimation of TMDC dipole moment variation obtained from measured photoluminescence (PL) spectra of WS2 monolayers in different solvents. An ability of such a system to tune the resonance coupling is realized experimentally for optically resonant spherical Si nanoparticles placed on a WS2 monolayer. The Rabi splitting energy obtained for this scenario increases from 49.6 meV to 86.6 meV after replacing air by water. Our findings pave the way to develop high-efficiency optoelectronic, nanophotonic and quantum optical devices.

physics.optics↗