The first measurements of the $\frac{1}{f}$-noise spectrum in copper oxide superconductors are presented. The key features of our results are (1) no noise is found in the superconducting state, (2) in the normal state the noise is large, comparable in magnitude to that in metal-insulator composites, and (3) the temperature dependencies of the noise and the resistivity are opposite, unlike either metals or semiconductors. Implications for possible conduction models are considered.

• Received 4 March 1988

DOI:https://doi.org/10.1103/PhysRevB.38.2922