Spectral compressibility at the metal-insulator transition of the quantum Hall effect

The spectral properties of a disordered electronic system at the metal-insulator transition point are investigated numerically. A recently derived relation between the anomalous diffusion exponent eta and the spectral compressibility chi at the mobility edge, chi = eta/2d, is confirmed for the integer quantum Hall delocalization transition. Our calculations are performed within the framework of a unitary network model and represent a new method to investigate spectral properties of disordered systems.