Breaking the Confinement-Loss Limit in Metals via Optical Antiskin Effect.

Guiding electromagnetic waves far below the diffraction limit usually produce severe propagation loss because the field is forced into dissipative material boundaries. We discover that a metal-Epsilon-near-zero (ENZ) interface can support an optical antiskin effect, significantly reducing propagation loss by orders of magnitude while preserving subdiffraction confinement. In the proposed metal-ENZ-high-index-air (MEHA) line, a nanoscale ENZ shell suppresses the lossy surface-bound mode and pushes it above a dielectric-confined mode in the modal hierarchy, allowing the low-loss volume mode to serve as the fundamental guided state. Realistic Ag/GaAs/Si MEHA lines support a mode-reordered terahertz band with robust bend transmission. This boundary-engineering mechanism establishes a compact, bend-tolerant, low-loss metallic-waveguide platform for high-density terahertz and midinfrared integration and localized wave delivery.