Enhanced Near-Field Scattering in Hyperbolic Materials at ENZ Frequencies

Materials operating near their epsilon-near-zero (ENZ) spectral regime have recently emerged as a powerful platform for extreme light–matter interactions. In this regime — defined by the vanishing of the real part of the dielectric permittivity  — theoretical works predict a variety of exotic responses, including super-Planckian thermal emission, near-perfect anomalous transmission, topological energy squeezing, and giant enhancement of local photonic density of states (LDOS). These effects arise from the ability of ENZ media to dramatically reshape the electromagnetic phase landscape, enabling unconventional control of directionality, coherence, and polarization in the near field.

In this work, we report experimental evidence of near-field super-scattering emerging in the vicinity of ENZ frequencies in 2D polar hyperbolic crystals. We demonstrate that, under ENZ conditions, α-MoO₃ can selectively amplify and redirect the incident electromagnetic field, acting as a spectral–polarization–directionality filter at nano to micrometer scales. Measurements conducted via scattering-type scanning near-field optical microscopy (s-SNOM), across both room and cryogenic temperatures, reveal a strongly enhanced and highly anisotropic redistribution of local fields around the ENZ resonance. These observations, fully supported by theoretical modeling, establish ENZ-driven super-scattering as a universal near-field phenomenon in polar hyperbolic media, opening routes toward directional thermal antennas, nanoscale wavefront sculpting, and quantum control of thermal radiation.