Enhanced nonlocal effects in metamaterials with moderate-index inclusions

We investigate a class of multilayered metamaterials characterized by moderate-index inclusions and low average permittivity. Via first-principle calculations, we show that in such scenario first- and second-order spatial dispersion effects may exhibit a dramatic and non-resonant enhancement, and may become comparable to the local response. Their interplay gives access to a wealth of dispersion regimes encompassing additional extraordinary waves and topological phase transitions. In particular, we identify a novel configuration featuring bound and disconnected isofrequency contours. Since they do not rely on high-index inclusions, our proposed metamaterials may constitute an attractive and technologically viable platform for engineering nonlocal effects in the optical range.