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

We propose a new mechanism of negative magnetoresistance in non-magnetic granular materials in which electron transport is dominated by hopping between two nearest-neighbor clusters. We study the dependence of magnetoresistance on temperature and separation between neighboring clusters. At a small separation we find a negative magnetoresistance at low temperatures and it changes over to a positive value as temperature increases. For a fixed temperature, magnetoresistance changes From negative to positive when the cluster separation increases. The change of magnetoresistance Delta R/R tan be more than 80 \% at low temperatures