Observations on small tunnel junctions: Anomalous critical-current temperature dependence, periodic structure, and microwave detection

Observations on very small Pb-Pb oxide-Pb tunnel junctions prepared by a new method are reported. The zero-voltage Josephson critical current is found to increase, then decrease with decreasing temperature. The current-voltage characteristics show very prominent periodic structure. The junctions have microwave (X-band) power sensitivities of 10^-14W, more than two orders of magnitude better than conventional-size junctions.