Electron-electron interaction effect on longitudinal and Hall transport in thin and thick Agx(SnO2)1-x granular metals

We study the temperature behaviors of the Hall coefficient, RH, and longitudinal conductivity, σ, of two series of Agx(SnO2)1-x (x being the Ag volume fraction) granular films lying in the metallic regime. The first (second) series of films are ∼500 (∼9) nm thick and constitute a three- (two-) dimensional granular array. In the high-x regime with gTgTc (gT being the dimensionless intergrain tunneling conductance, and gTc being the critical tunneling conductance at the percolation threshold), we observe a RHlnT law from ∼6 to 300 K. This lnT behavior is independent of array dimensionality. We also observe a σlnT law in the temperature range ∼20-100 K. Below ∼10 K, the temperature behavior of σ changes to a T dependence in thick films, while it changes to a different lnT dependence in thin films. The overall RH and σ characteristics can be explained by the electron-electron interaction (EEI) effects in the presence of granularity. As x is reduced and approaches the percolation threshold, we found that the lnT dependences of RH and σ still hold for a wide temperature range. We propose an explanation for the long-standing puzzle of the σlnT dependence, which has previously been frequently observed in composite systems near the quantum percolation threshold, as arising from the same EEI effect considered in the recent theory of granular metals.