High Tc's in Ultra-Thin Films

Abstract

Measurements are reported which show that the maximum Tc that has been reached in quenched ``soft-metal'' films is correlated with the maximum Tc computed from the analysis of McMillan,1 assuming an optimum value for the electron-phonon coupling. The enhanced electron-phonon coupling may be attributed to the lowering of the phonon frequencies, which would be caused by the small metallic grains and greatly increased surface area expected in these porous quenched films. Molecular dynamics calculations by Dickey and Paskin2 indicate that the changes in the phonon frequencies in small particles are large enough to account for the changes in Tc. Data are presented which show that the region with the greatest increase in Tc occurs within a few monolayers of the metal-vacuum, metal-insulator, or metal-metal surfaces.3 If similar, near monolayer structures of, high Tc, transition metal alloys can be made, temperatures above 25°K should be possible.