Granular Al-Ge films, just on the metallic side of the critical volume fraction φc(50.7% Al), are found to have critical fields in excess of 1.5T at 0.47 K due to the fine granular nature of the Al. In barely insulating films where φc- φ < 2.2% (φ is the volume fraction of aluminum), Josephson junction coupling dominates the behaviour below Tc. For 3.4% ≤ (φ - φ) ≤ 6.2%, the resistivity diverges strongly below Tcand a large negative magnetoresistivity (MR) is observed. This behaviour is explained in terms of quasiparticle tunnelling or alternatively by the Adkins charging model. The high negative MR is explained using a magnetic field-dependent superconducting energy gap. The normal resistivity in the insulating films obeys the hopping relation ρ = ρ0exp(T0/T)xabove Tcand also below Tcin a field of 3.45 T, which quenches all superconductivity in the Al below Tc= 1.61 K. © 1994.
Mendeley saves you time finding and organizing research
Choose a citation style from the tabs below