Shivaksh Rawat | Searcharxiv

arXiv2026

Generation and Enhancement of Persistent Nanoscale Magnetization in All-Dielectric Metasurfaces by Optically Injected and Localized Free Carriers

Time-varying dielectric metasurfaces that support sharp optical resonances with nontrivial electromagnetic field distributions constitute a unique platform for realizing temporal interfaces for metasurface-guided waves (MGWs). Rapidly changing metasurface resonance enables frequency conversion and temporal scattering of a concurrently propagating MGW. Using analytical methods and electromagnetic simulations, free carriers are generated locally to create frequency-shifted infrared MGWs. Such time interfaces can be utilized to generate large, highly localized quasistatic magnetic fields within the metasurfaces. The resulting nanoscale magnetization, supported by the residual circulating currents, persists for several optical cycles after the departure of the time-scattered MGWs. During the rectification process, the initial electromagnetic energy of the injected MGWs is partitioned between the temporally scattered MGWs, the residual motion of the free carriers, and a quasistatic magnetic field.

physics.optics↗

arXiv2026

Probing Azimuthal Anatomy of Hyperbolic Whispering Gallery Modes in hBN

Scattering-type scanning near-field optical microscopy (s-SNOM) is a powerful tool for investigating polaritonic modes. However, an inherent limitation of this technique is that excitation and detection occur at the same location. This constraint makes it challenging to resolve excitations with complex spatial structures, which can exhibit delicate dependence on the in-coupling conditions. Here, we present a strategy to overcome this limitation by introducing an auxiliary cavity, which serves as a stationary near-field excitation source. This configuration allows the s-SNOM tip to act solely as a detector, and decouples excitation from detection. We apply this approach to whispering gallery modes (WGMs) of hyperbolic phonon-polaritons in hexagonal boron nitride resonators. Through spatially resolved near-field maps we directly observe subwavelength polaritonic WGMs with large and discrete azimuthal momentum ($k_ϕ/ k_0$ up to 15). This allows us to map the frequency and angular behavior of the modes. Notably, we observe dynamic tuning of the effective refractive index by the WGMs to preserve consistent azimuthal momentum $k_ϕ$ under varying excitation conditions. Numerical simulations support the experimental observations and confirm the observation of hyperbolic WGMs. This approach enables direct visualization of previously hidden mode structures in hyperbolic cavities and opens new pathways for momentum-controlled polaritonic device engineering.

cond-mat.mes-hall↗