Anomalous Diffusion at the Anderson Transitions

Diffusion of electrons in three dimensional disordered systems is investigated numerically for all the three universality classes, namely, orthogonal, unitary and symplectic ensembles. The second moment of the wave packet <r²(t)> at the Anderson transition is shown to behave as ~ tᵃ (a≈ 2/3). From the temporal autocorrelation function $C(t)$, the fractal dimension D₂ is deduced, which is almost half the value of space dimension for all the universality classes.