POWER-LAW CORRECTIONS TO THE KUBO FORMULA VANISH IN QUANTUM HALL SYSTEMS

In first order perturbation theory conductivity is given by the Kubo formula, which in a Quantum Hall System equals the first Chern class of a vector bundle. We apply the adiabatic theorem to show that these topological constraints quantize the averaged conductivity to all orders of perturbation theory. Hence the Kubo formula is valid to all orders. © 1990 Springer-Verlag.