Lattice Vibrations and Superconductivity in Layered Structures

In order to estimate the influence of both surface and interface effects on phonon frequencies and superconducting transition temperatures in layered structures, we have calculated the vibrational modes of structures composed of alternating films of heavy and light particles. An interface effectively lowers the vibrational frequencies of the heavy particles and raises those of the light particles. Interface effects are small compared to surface effects, however. The decrease in the frequencies for a three-layer film on a substrate (with respect to the bulk frequencies) is only 40—50% of the decrease for a free three-layer film.