Quasireentrant superconductivity near the metal-insulator transition of granular aluminum

Incomplete superconducting transitions, often called quasireentrant, have been observed in the resistivity of three-dimensional granular aluminum very close to the metal-insulator transition. An even more pronounced signature of these transitions is evident in the magnetic field dependence at temperatures well below the superconducting transition temperature. The effect in the temperature dependences is similar to behavior observed in discontinuous thin films which has been attributed to macroscopic quantum tunneling. No corresponding measurements or theoretical predictions of the magnetic field dependence have yet been reported.