Near-Field Nanospectroscopy and Mode Mapping of Lead Telluride Hoppercubes

Lead chalcogenides are compelling materials for nanophotonics and optoelectronics due to their high refractive indices, extreme thermo-optic coefficients, and high transparency in the mid-infrared (MIR). In this study, PbTe hoppercubes (HC, face-open box cubes) are synthesized and explored for their MIR resonant characteristics. Single-particle microspectroscopy uncovered deep-subwavelength light localization, with a spectral response dominated by both fundamental and multiple high-order Mie-resonant modes. Nanoimaging mapping using scattering-type scanning near-field optical microscopy (s-SNOM) reveals that the scattering at the center of the HC is reduced by more than five times compared to the edges. 2D-Hyperspectral scans conducted using a low-power broadband MIR source and nanometer spatial resolutions provided information on the local amplitude and phase-resolved near-fields, including amplitude and phase mapping of higher order modes with measured Q-factors of close to 100. Employing s-SNOM to characterize complex resonant nanophotonic structures holds implications for quantum sensing, IR photodetection, non-linear generation, and ultra-compact high-Q metaphotonics.