ACOUSTIC TRANSMISSION SPECTRA IN THE PENROSE LATTICE

Employing third sound in a superfluid helium film as an acoustic wave, transmission spectra are measured experimentally in the Penrose latti ce. The spectra are extremely sensitive to the impinging direction of third sound. The transmissivity is suppressed strongly at certain freq uency ranges. A transparent direction of the Penrose lattice is found simultaneously. We attribute the origin of the prominent suppressions of transmissivity to the multiple diffraction of third sound in the Pe nrose lattice.