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 \approx 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) \propto \exp (1/T) (for T \leq 20 K) and R(U) \propto \exp (1/U)) (for T \leq 1 K and U > 0.1 V) are observed. Magnetoresistance (MR) is negative and can be described by \Delta R(H)/R(0) \propto -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. 
B. I. Belevtsev, E. Yu. Beliayev, Yu. F. Komnik, E. Yu. Kopeichenko   (B. Verkin Institute for Low Temperature Physics & Eng...