ACTIVATED RESISTIVITIES IN THE INTEGER QUANTUM HALL-EFFECT

We have determined the off-diagonal and diagonal conductivities for a quantum Hall system at exactly integer filling at finite temperatures and in the presence of a weak short ranged disorder potential within t he self-consistent Born approximation. We find that there is a finite temperature contribution to off-diagonal conductivity sigma(xy) which also can be independent of impurity concentration. The diagonal conduc tivity sigma(xx) also survives only when both temperature and disorder are nonzero. At low temperatures, sigma(xx) activates with a temperat ure dependent prefactor. Inverting the conductivity matrix, we determi ne the resistivities. The deviation of the off-diagonal resistivity rh o(xy) from its zero temperature value and the diagonal resistivity rho (xx) activate with a temperature dependent prefactor at low temperatur es, in agreement with experiments. Further, we find two physical regim es both of which are at low temperatures and low broadening, which pro vide the experimentally observed linear relationship between the devia tion of rho(xy) and the rho(xx) with different signs. We have also est imated the effective masses from the experimental data of rho(xy) and find them to be reasonable. Finally, our result on compressibility as a function of temperature shows that there is no phase transition invo lved in the system as far as the temperature is concerned.