  Magnetotransport measurements in combination with molecular dynamics (MD)
simulations on two-dimensional disordered Lorentz gases in the classical regime
are reported. In quantitative agreement between experiment and simulation, the
magnetoconductivity displays a pronounced peak as a function of perpendicular
magnetic field $B$ which cannot be explained in the framework of existing
kinetic theories. We show that this peak is linked to the onset of a directed
motion of the electrons along the contour of the disordered obstacle matrix
when the cyclotron radius becomes smaller than the size of the obstacles. This
directed motion leads to transient superdiffusive motion and strong scaling
corrections in the vicinity of the insulator-to-conductor transitions of the
Lorentz gas.
