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

Abstract

We study the temperature behaviors of the Hall coefficient, R-H, and longitudinal conductivity, sigma, of two series of Ag-x(SnO2)(1-x) (x being the Ag volume fraction) granular films lying in the metallic regime. The first (second) series of films are similar to 500 (similar to 9) nm thick and constitute a three-(two-) dimensional granular array. In the high-x regime with g(T) >> g(T)(c) (g(T) being the dimensionless intergrain tunneling conductance, and g(T)(c) being the critical tunneling conductance at the percolation threshold), we observe a R-H alpha ln T law from similar to 6 to 300K. This ln T behavior is independent of array dimensionality. We also observe a sigma alpha ln T law in the temperature range similar to 20-100 K. Below similar to 10 K, the temperature behavior of sigma changes to a root T dependence in thick films, while it changes to a different ln T dependence in thin films. The overall R-H and sigma 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 ln T dependences of R-H and sigma still hold for a wide temperature range. We propose an explanation for the long-standing puzzle of the sigma alpha ln T 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.