The insulating-to-superconducting transition in europium high-temperature superconducting ceramics

Experiment resistivity data on high-temperature superconducting ceramics of fully oxygenated EuBa₂Cu₃-_xCo_xO_y, show that the insulating-to-superconducting transitions take place at liquid-helium temperature, provided that the cobalt fraction × exceeds 0.3. The resistivity follows a simple power-law dependence ρ α T^-1/2 attributed to electron-electron interactions. A model based upon intrinsic Josephson tunnelling junctions is suggested to explain the transition from insulating to superconducting states.