Interferometric\nNear-field Fano Spectroscopy of Single\nHalide Perovskite Nanoparticles

Semiconducting halide perovskite nanoparticles support\nMie-type\nresonances that confine light on the nanoscale in localized modes\nwith well-defined spatial field profiles yet unknown near-field dynamics.\nWe introduce an interferometric scattering-type near-field microscopy\ntechnique to probe the local electric field dynamics at the surface\nof a single MAPbI<sub>3</sub> nanoparticle. The amplitude and phase\nof the coherent light scattering from such modes are probed in a broad\nspectral range and with high spatial resolution. In the spectral domain,\nwe uncover a Fano resonance with a 2π phase jump. In the near-field\ndynamics, this Fano resonance gives rise to a destructive interference\ndip after a few femtoseconds. Mie theory suggests that the interference\nbetween electric quadrupole and magnetic dipole modes of the particle,\nwith spectra affected by resonant interband absorption of MAPbI<sub>3</sub>, lies at the origin of this effect. Our results open up a\nnew approach for probing local near-field dynamics of single nanoparticles.