Effect of the transition from the normal state to the superconducting state on the phonon transmission through liquid 4He-metal interface
Zinov'eva K. N., Narmoneva D. A., Semenov A. S.
The passage of low-frequency phonons through the liquid 4He~aluminum single-crystal interface has been studied. The measurements were carried out at temperatures 100-300 mK and frequencies 13-91 MHz for normal and superconducting states of aluminum. It is demonstrated that Rayleigh wave contribution to the total energy flux across the boundary decreases markedly on going from the normal state to the superconducting state of the metal. Experimental data are compared with the data on copper reported previously. It is concluded that the scattering of surface waves (similarly to the bulk waves) is due to conduction electrons. The bulk interference of phonons (analogous to the Fabry-Perot interference) has been observed for a superconducting metal, while for the normal state this effect is absent.