Critical-Cone Channeling of Thermal Phonons at a Sapphire-Metal Interface

Abstract

A new structure has been observed in the phonon focusing pattern of a highly polished sapphire crystal with a metalized surface. It corresponds to a concentration of transverse phonons close to the critical cone for mode conversion between transverse and longitudinal waves. This wave-vector channeling effect is interpreted in terms of evanescent longitudinal waves at a weakly bonded sapphire-metal interface.