arXiv subjects

Fuxing Gu

Publications and source records attributed to Fuxing Gu.

5 recordsLinked to original sources

arXiv2026

Self-referenced, drift-tolerant dipole-resolved population inversion using degeneracy-lifted dual quasinormal modes

Photoluminescence intensity is widely used to infer exciton populations, yet the detected signal inherently convolves occupancy with radiative-rate modification and collection efficiency, making quantitative inversion vulnerable to pump and system drifts. Here we realize a dual-channel self-referenced scheme enabled by two nearly degenerate quasinormal modes in a hybrid microcavity. Their shared optical path provides common-mode observables (i.e., overall spectral and intensity drift) that track global thermo-optic and pump fluctuations, while their differential-mode observables (i.e., spectral splitting and mode-contrasted emission) remain highly sensitive to local gap dielectric perturbations and dipole-dependent radiative weights. Using temperature as a control parameter in monolayer WSe$ _2 $, we exploit this common/differential-mode framework to robustly invert the relative populations of excitons with out-of-plane ($ \perp $) and in-plane ($ \parallel $) dipole transitions without external absolute calibration. At the temperature of $\sim$50 K, we obtain $ N_\perp/N_\parallel \approx 200 $, coincident with the expected accumulation in the out-of-plane-emitting dark manifold. This internally referenced approach provides a practical route to drift-tolerant, dipole-resolved population metrology in nanogap photonic systems.

physics.optics↗

arXiv2026

Population Metrology of a Hidden Exciton Reservoir: Quasi-Thermalization versus Localization

Long-lived dark states can dominate the lowest-energy manifold of optically driven quantum materials, yet their occupation remains difficult to quantify, leaving it unclear whether it reflects thermal redistribution or kinetic trapping. We combine microsphere-enabled far-field access with quantitative optical-response calibration to retrieve dark-to-bright population ratios in monolayer WSe2. Temperature-dependent measurements and controlled defect enhancement separate mobile and localized contributions. Near room temperature, the mobile dark-to-bright ratio reaches approximately 65% of its Boltzmann limit, indicating substantial but incomplete quasi-thermalization, whereas the low-temperature excess is dominated by defect-assisted localization. Dark-state dominance alone therefore does not establish equilibration, a distinction essential for interpreting transport and collective phases in optically hidden quasiparticle reservoirs.

physics.optics↗

arXiv2025

Direct observation of room-temperature exciton condensation

Exciton condensation--an interaction-driven, macroscopically coherent paired-fermion state--offers the prospect for dissipationless energy transport in solids, akin to that in superconductivity. Although their light effective mass and strong Coulomb binding favour high transition temperatures, convincing demonstrations of pure-exciton condensation have hitherto been limited to cryogenic conditions. Here, we report the direct observation of quasi-equilibrium condensation of dark excitons in monolayer tungsten diselenide at 300 K and ambient pressure. We achieve this by creating nanoscale spacing-graded Stark traps to confine free excitons, setting the finite-size scale, non-resonant off-axis optical injection to control the local density-temperature trajectory, and employing surface plasmon polariton-enhanced microsphere-assisted microscopy to boost dark-exciton emission and directly image first-order spatial coherence with sub-diffraction resolution. We observe a sharp degeneracy threshold and a clear phase transition, evidenced by extended first-order spatial coherence with algebraic decay and a critical exponent consistent with the universal Berezinskii-Kosterlitz-Thouless criterion. Identical condensation signatures are observed in over 30 independent samples. Our work establishes a room-temperature excitonic platform for exploring strongly correlated many-body physics and advancing near-dissipationless, coherent quantum technologies.

physics.optics↗

arXiv2025

In-situ dynamic spatial reconfiguration of nanoplasmonics using photothermal-shock tweezers

Dynamic reconfiguration is crucial for nanoplasmonic structures to achieve diversified functions and optimize performances; however, the dynamic reconfiguration of spatial arrangements remains a formidable technological challenge. Here, we showcase in-situ dynamic spatial reconfiguration of plasmonic nanowire devices and circuits on dry solid substrates, by harnessing a photothermal-shock tweezers platform. Owing to its versatility, nanoscale precision, real-time operation, and large external output force, the multimodal platform enables dexterous fine-tuning of positions, overlap lengths, and coupling distances and orientations of discrete components in situ. Spatial position-dependent optical properties that have not been reported before or are challenging to achieve through traditional micro/nanomanipulation are easily tuned and observed, such as the intensity evolution of axial photon-plasmon coupling from near field to far field, and the resonant mode evolution of photonic cavity-plasmonic cavity coupling from weak to strong. We also employ the nanorobotic probe-based operation mode to optimize the side-mode suppression ratios of single-mode lasers and the intensity splitting ratios of 3-dB couplers. Our results are general and applicable to materials of almost any size, structure, and material type, as well as other narrow or curved micro/nano-waveguide surfaces, which opens new avenues for reconfigurable nanoplasmonic structures with dynamically tunable spatial features.

physics.optics↗

arXiv2012

Multicolour wavelength-tunable lasing from a single bandgap-graded alloy nanoribbon

Tunable lasing from 578 nm to 640 nm is observed from a single CdSSe bandgap-graded alloy nanoribbon, by selecting the excited spot at room temperature. Though reabsorption is a serious problem to achieve lasing at short wavelength, multiple scatters on the nanoribbon form localized cavities, and thus realize lasing at different wavelengths. By increasing the excitation area, we also observe multicolour lasing from the same nanoribbon simultaneously.

physics.optics↗