Temperature-independent behavior of the Hall constant in granularIn2O3−xfilms

In insulating, three-dimensional films of granular ${\mathrm{In}}_2$ ${\mathrm{O}}_{3\mathrm{-}\mathrm{x}}$, the resistance behavior is well described by the Mott variable-range-hopping (VRH) expression, R∝exp($T_{\mathrm{Mott}/\mathrm{T}{)}^{1/4}}$; this Mott VRH dependence of the resistance is observed in the liquid-helium to liquid-nitrogen temperature regime. In the same temperature interval, the Hall constant $R_H$ is observed to be independent of temperature. This result is in conflict with the theoretical prediction of Gruenewald et al., where an temperature dependence is anticipated.