Quench-condensed indium-hydrogen films. II. Changes in electric and superconducting characteristics near the metal-insulator transition

Abstract

Electrical and superconducting properties of indium films condensed in a H2 atmosphere (pressurep H 2=6×10−6 to 1.4×10−4 Torr) onto a substrate cooled with liquid helium are investigated. As hydrogen content is increased, a continuous increase in residual resistivity ρ* is observed, permitting systematic study of the resistance vs. temperature dependenceR(T) and the superconducting transition temperatureT c on approaching the metal-insulator transition (MIT). With regard to ρ*, four regimes of conductivity can be observed: (1) conductivity with a positive temperature resistance coefficient (TRC), (2) conductivity with a small, constant, negative TRC, (3) conductivity under weak localization with ΔR (T) ∼ln T or $$ \sim \sqrt T $$ type corrections, (4) hopping conductivity.T c rises continuously with ρ* and reaches its peak (∼5.2K) in the second regime. A further increase of ρ* leads to a decrease ofT c and complete suppression of superconductivity. The experimental dependenceR(T) is compared with theory. TheT c variation on approaching the MIT and the relation between Mooij's rule and the superconducting properties are discussed.