Baù, E., Aigner, A., Biechteler, J., Heimig, C., Weber, T., Gölz, T., Maier, S. A., Tittl, A. (2026). Spatially Encoded Polaritonic Ultra‐Strong Coupling in Gradient Metasurfaces with Epsilon‐Near‐Zero Modes. Advanced Materials. https://doi.org/10.1002/adma.202510402