The level-shifting-induced negative magnetoresistance in the nearest-neighbor hopping conduction

We propose a new mechanism of negative magnetoresistance in non-magnetic gr anular materials in which electron transport is dominated by hopping betwee n two nearest-neighbor clusters. We study the dependence of magnetoresistan ce on temperature and separation between neighboring clusters. At a small s eparation we find a negative magnetoresistance at low temperatures and it c hanges over to a positive value as temperature increases. For a fixed tempe rature, magnetoresistance changes From negative to positive when the cluste r separation increases. The change of magnetoresistance Delta R/R tan be mo re than 80 % at low temperatures.