All-optical bistability based on coupled epsilon-near-zero Tamm states.

Optical bistability in epsilon-near-zero (ENZ) materials holds promise for all-optical switching but is typically restricted to TM-polarized light at oblique incidence, with high-intensity damping often overlooked. Here, by exploiting Tamm states at a photonic-crystal-ENZ interface, we demonstrate optical bistability over a broad range of incident angles for both polarizations. We show that shifting perfect absorption to higher electron temperatures in the ENZ layer enhances bistability, while reducing the photonic crystal layer thickness enables shorter-wavelength operation without increasing carrier concentration, preserving strong nonlinearity. This approach provides a practical strategy for bistable photonic devices with broadband angular and polarization performance.