  As a function of the disorder strength in a mesoscopic system, the electron
dynamics crosses over from the ballistic through the diffusive towards the
localized regime. The ballistic and the localized situation correspond to
integrable or regular behavior while diffusive conductors correspond to chaotic
behavior. The chaotic or regular character of single wave functions can be
inferred from phase space concepts like the Husimi distribution and the Wehrl
entropy. These quantities provide useful information about the structure of
states in disordered systems. We investigate the phase space structure of one
dimensional (1d) and 2d disordered systems within the Anderson model. The Wehrl
entropy of the eigenstates allows to detect the crossover between the
ballistic, diffusive and localized regime.
