Frequency dependent transport in the integer quantum Hall effect

The frequency dependent transport is investigated for a two-dimensional disordered system under QHE conditions. The real and imaginary parts of the conductivity are calculated numerically in linear response using a recursive Green function technique. The energy dependence of $\sigma_{xx}(E,\omega)$ is obtained within the lowest Landau band. When the width of the system exceeds the characteristic length, $L_{\omega}=(\hbar\omega \rho(E))^{-1/2}$, the maximum of the real part of $\sigma_{xx}(E,\omega)$ decays with frequency almost linearly which is different from the classical Drude behaviour.