Extraordinary Optical Transmittance Generation on Si3N4 Membranes

Metamaterials have been recently attracting increasing attention thanks to their capability to go beyond the electromagnetic and transport properties of natural materials. Although less developed compared to plasmonic systems, phononic metamaterials offer the advantage of controlling phonon propagation and, consequently, heat transfer at a microscopic level, and strong local field enhancement in the infrared. In this work, extraordinary optical transmittance (EOT) from insulating silicon nitride (Si3N4) membranes patterned with a periodic lattice of micrometric circular holes (3, 5, 7 μm) is achieved. By performing transmittance measurements in the infrared, the coupling between an incoming electromagnetic wave and an optical phonon is obtained, triggering an increase in the transmitted intensity in an otherwise opaque phonon spectral region. This induced transparency effect can be explained in terms of a phonon-polariton generation as also demonstrated by nano-resolved infrared imaging.