Logarithmic temperature dependence of Hall transport in granular metals

We have measured the Hall coefficient R_H and the electrical conductivity σ of a series of ultrathin indium-tin-oxide films between 2 and 300 K. A robust R_HlnT law is observed in a considerably wide temperature range of 2 and ∼120K. This lnT dependence is explained as originating from the electron-electron interaction effect in the presence of granularity as theoretically predicted. Furthermore, we observed a σlnT law from 3 K up to several tens K, which also arose from the Coulomb interaction effect in inhomogeneous systems. These results provide strong experimental support for the current theoretical concepts for charge transport in granular metals with intergrain tunneling conductivity g_T1.