Breaking the Moss rule

TL;DR

This review explores super-Mossian dielectrics that break the traditional Moss rule, offering high refractive indices and transparency, which could revolutionize photonic device performance.

Contribution

It surveys materials surpassing the Moss rule, discusses their electronic structures, and highlights computational screening methods for discovering these advanced dielectrics.

Findings

Super-Mossian dielectrics exhibit high refractive indices with wide transparency.

Electronic band structures with large joint density of states enable super-Mossian behavior.

Refractive index limits define performance boundaries for photonic nanodevices.

Abstract

Photonic devices depend critically on the dielectric materials from which they are made, with higher refractive indices and lower absorption losses enabling new functionalities and higher performance. However, these two material properties are intrinsically linked through the empirical Moss rule, which states that the refractive index of a dielectric decreases as its band gap energy increases. Materials that surpass this rule, termed super-Mossian dielectrics, combine large refractive indices with wide optical transparency and are therefore ideal candidates for advanced photonic applications. This Review surveys the expanding landscape of high-index dielectric and semiconductor materials, with a particular focus on those that surpass the Moss rule. We discuss how electronic band structures with a large joint density of states near the band edge give rise to super-Mossian behavior and how first-principles computational screening can accelerate their discovery. Finally, we establish how the refractive index sets the performance limits of nanoresonators, waveguides, and metasurfaces, highlighting super-Mossian dielectrics as a promising route toward the next performance leap in photonic technologies.