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

The low-temperature (0.5-55 K) conduction of semicontinuous gold film vacuum deposited at T approximate to 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) proportional to exp(1/T) (for T less than or equal to 20 K) and R(U) proportional to exp(1/U)) (for T less than or equal to 1 K and U > 0.1 V) are observed. Magnetoresistance (MR) is negative and can be described by Delta R(H)/R(0) proportional to - 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. (C) 1998 Elsevier Science B.V. All rights reserved.