Activated Conductivity in the Quantum Hall Effect

A prefactor of the activated dissipative conductivity in the quantum Hall regime is studied in the case of a short-range random potential. Two major contributions to the conductivity are calculated explicitly: one of a narrow band of delocalized states which appears at a finite temperature near the Landau level center and the related to hopping between localized states in the shallow tail of the density of states. It is shown that interplay of these contributions yields the prefactor which depends very weakly on the electron-phonon coupling constant and is close to e²h under the experimental conditions.