SOME REMARKS ON VARIABLE RANGE HOPPING - IN PARTICULAR IN THE QUANTUM HALL REGIME

An expression for the heat conductivity κxx is derived in the effective medium approximation. Mott type formulas are obtained for κxx and the Peltier coefficient βxx. Using percolation theory in a three-dimensional system the Wiedemann-Franz ratio was found to depend on the temperature like {Mathematical expression}. The Mott type formulas were evaluated in a similar way for a two-dimensional system in the quantum Hall regime within the high-field percolation model. In contrast to previous calculations of the high field hopping conductivity σxx, the results are fully consistent with the experimental data on σxx and the density of states at the Fermi level. Finally, βxx is estimated which together with σxx and σxy=ie2/h(i=0,1,2,...), determines both thermopower coefficients αxx and ασxy. © 1990 Springer-Verlag.