LQ11225B
Unusual dependence of the superconductivity on the thickness of MoGe films.
Thin films of MoGe show progressively reduced superconducting transition temperatures as their thickness is decreased. The optical conductivity has been obtained from far-infrared transmission and reflection measurements for a set of such films. The absorptive part of this conductivity shows a clear energy gap whereas the dispersive part measures the superfluid density. The superfluid density decreases as thickness (and transition temperature) is reduced, whereas the ratio of the gap to the transition temperature, a measure of the strength of the pairing interaction, is unchanged. The normal state properties (e.g., the resistivity) also do not change. Although the result that the transition temperature is suppressed in thin films, even though the basic electronic properties and the strength of the superconducting pairing interactions in the metal do not change, initially seems to contain contradicitons, detailed theoretical calculations, using a sophisticated theory of superconductivity, do provide an explanation of the results. However, the measurements also find that the expected coherence peak in the optical scattering rate is lost in the thinner samples, a result which cannot be explained within conventional theories.
