Metal-insulator nanocomposites which act optically like homogeneous conductors

Abstract

Conductor-insulator nanocomposites in which the conductor percolates can have optical responses at longer wavelengths like dense conductors with an effective plasma frequency wp*. This applies at wavelengths where the Bergman spectral function F for permittivity varies sufficiently slowly with wavelength. wp* can be engineered by varying the components, the nanostructure's topology, or the dielectric volume fraction f. The homogenized conductor acts like a dense conductor whose charge carriers have effective mass meff*. Results are presented for wp*(f) and meff*(f) using the Maxwell Garnett (MG) and Bruggemann (BR) models for spheres and aligned ellipsoids. In the BR case meff*(f) at the percolation concentration is singular. Example wp* data for spheres and ellipsoids are given which match predictions. Anisotropy in effective mass is considered, such that effective plasma frequency can depend strongly on polarisation direction of incident light.