SUPERCONDUCTING INTERLAYER COUPLING OF NBN/X (X=AG, CNX) MULTILAYERED FILMS

The interlayer coupling of superconducting NbN thin films through metallic Ag and insulating CNx thin films have been investigated from resistivity measurements of [NbN(170 Angstrom)/X(t Angstrom)](10) (X = Ag, CNx) multilayered films. When Ag layer thicknesses are thicker than 150 Angstrom, NbN layers are decoupled and the transition temperatures are nearly equal to 8.2 K. The transition temperature increases with decreasing Ag layer thickness, obeying Werthamer's theory for the proximity effect. On the other hand, with the increase of CNx layer thickness, the transition temperature is lowered steeply and almost linearly, indicating a coupling mechanism other than the proximity effect.