THE INSULATING-TO-SUPERCONDUCTING TRANSITION IN EUROPIUM HIGH-TEMPERATURE SUPERCONDUCTING CERAMICS

Experiment resistivity data on high-temperature superconducting cerami cs of fully oxygenated EuBa2Cu3-xCoxOy show that the insulating-to-sup erconducting transitions take place at liquid-helium temperature, prov ided that the cobalt fraction x exceeds 0.3. The resistivity follows a simple power-law dependence rho proportional to T--1/2, attributed to electron-electron interactions. A model based upon intrinsic Josephso n tunnelling junctions is suggested to explain the transition from ins ulating to superconducting states.