The transition from a positive to a negative temperature coefficient of resistivity (TCR) has been studied in the artificially layered metallic system Nb-Cu. We find the TCR to undergo a rather sudden change in sign from positive to negative as the layer thickness is decreased below approximately 10 Å. The temperature dependence of the conductivity in the nonmetallic regime can be explained by localization-type theories, and implies that both localization and Coulomb effects are important in this purely metallic three-dimensional system.

• Received 7 April 1982

DOI:https://doi.org/10.1103/PhysRevB.26.2224