Negative magnetoresistance in the nearest-neighbour hopping conduction in granular gold film

Abstract

The low-temperature (0.5–55 K) conduction of semicontinuous gold film vacuum deposited at T≈50 K is studied. The film is near the percolation threshold (thickness 3.25 nm). Its resistance is extremely sensitive to the applied voltage U. At low enough U the film behaves as an insulator (two-dimensional granular metal). In this state the dependences R( T)∝exp(1/ T) (for T⩽20 K) and R( U)∝exp(1/ U)) (for T⩽1 K and U>0.1 V) are observed. Magnetoresistance (MR) is negative and can be described by Δ R( H)/ R(0)∝− H 2/ T. This negative MR which manifests itself for nearest-neighbour hopping is rather uncommon and, up to now, has not been clarified. The possible mechanisms of such case of negative MR are discussed.