Tunable phononic transparency and opacity with isotopic defects

In an isotopically disordered harmonic chain, phonon transmission attenuates exponentially with distance because of multiple scattering by the isotopic defects. We propose a simple method, which is based on the static structure factor, for arranging the isotopic defects to suppress or enhance phonon scattering within a targeted frequency window, resulting in maximization or minimization of phonon transmission. The phononic transparency and opacity effects are demonstrated numerically from the frequency dependence of the transmission coefficient. We briefly discuss how the underlying concept can be extended to the design of aperiodic superlattices to improve or block phononic transmission.