Optical properties and electronic structures of intrinsic gapped metals: Inverse materials design principles for transparent conductors.

This article examines the optical properties of intrinsic gapped metals—materials characterized by an internal bandgap and a high concentration of free carriers without intentional doping—and their potential as transparent conductors. It categorizes gapped metals into three types based on their electronic structures and optical behavior: (i) those with strong intraband absorption in the visible range (e.g., CaN₂), (ii) those with strong interband absorption in the visible range (e.g., NbCoSb and SrNbO₃), and (iii) those with optimal carrier concentration and internal bandgap suitable for transparency and conductivity (e.g., Sr₅Nb₅O₁₇). The study highlights that a large internal bandgap alone does not guarantee transparency, as free carrier absorption and transitions within partially filled bands significantly affect optical properties. It proposes design principles emphasizing the balance of carrier concentration and band structure to guide the discovery of next-generation transparent conductors among gapped metals.