Observation of superconducting transition temperature oscillations in metal--nonmetal film systems

For technetium-carbon, molybdenum-carbon, and vanadium-carbon thin-film layer structure an oscillatory dependence of the superconducting transition temperature on carbon layer thickness is found. The oscillation take place for thin metal layers (d<300A) and for very small thickness of the nonmetal film (d/sub c/<30A). In addition to the oscillations of T/sub c/, oscillations of the normal-state electrical resistance remaining up to room temperture are found in the layered samples. A correlation is observed between critical temperature and resistance changes; Maxima in the curve T/sub c/(d/sub c/) correspond to minima in rho (d/sub c/). The amplitude of the critical temperature oscillations is 10--15% of the T/sub c/ value and depends on the metal layer thickness, increasing with decreasing d approximately as 1/d. also found in the thin-film layer structures are oscillations of the critical magnetic fields H/sub cn/ and H/sub c/parallel correlating with T/sub c/ oscillations. A mutual influence of nonmetal layers located on opposite sides of the metal film was observed