Computational discovery and experimental validation of high-refractive index HfS2 nanoresonators.

High-refractive index dielectric materials can enhance many optical technologies by enabling efficient light manipulation in waveguides, metasurfaces, and nanoscale resonators. Van der Waals materials, which are anisotropic semiconductor materials, are particularly promising due to their excitonic response and strong in-plane polarizability. Here, we perform ab initio calculations to determine the refractive index of over a hundred anisotropic semiconductor materials, many of them van der Waals in nature. Our computational screening reveals both established and less-explored promising materials, including hafnium disulfide (HfS2), which exhibits an in-plane refractive index above 3 and large anisotropy in the visible range. We confirm these properties through ellipsometry and develop a nanofabrication process for HfS2, demonstrating Mie-resonant nanodisks. This is achieved by mitigating the air sensitivity of HfS2 through storage in controlled environment or encapsulation. Our work provides a comparative overview of high-index van der Waals materials and establishes HfS2 as a promising material for visible-range photonics.