Resistivity and magnetoresistivity near the metal-insulator and superconductor-insulator transition in granular Al-Ge

G. Eytan*, E. Zaken, R. Rosenbaum, D. S. McLachlan, A. Albers

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

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 Tc and 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 = ρ0 exp(T0/T)x above Tc and also below Tc in a field of 3.45 T, which quenches all superconductivity in the Al below Tc = 1.61 K.

Original languageEnglish
Pages (from-to)240-244
Number of pages5
JournalPhysica A: Statistical Mechanics and its Applications
Volume207
Issue number1-3
DOIs
StatePublished - 1 Jun 1994

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