Absence of superconductivity in metallic granular aluminum

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Abstract
Granular aluminum near the metal-insulator transition has been found to have a range of metal concentrations over which it is metallic (M) but not superconducting (S). For higher concentrations it is superconducting and at lower concentrations insulating (I). There is a striking resemblance of the temperature dependence of resistivity in the S,M, and I ranges of granular aluminum to the temperature dependence of sheet resistance in very thin quench-condensed films. However there is as yet no theory that gives a satisfactory explanation of this behavior in both two- and three-dimensional systems.