  The emergence and vanishing of superdiffusion in quasi-two-dimensional Yukawa
systems are investigated by molecular dynamics simulations. Using both the
asymptotic behaviour of the mean-squared displacement of the particles and the
long-time tail of the velocity autocorrelation function as indicators for
superdiffusion, we confirm the existence of a transition from normal diffusion
to superdiffusion in systems changing from a three-dimensional to a
two-dimensional character. A connection between superdiffusion and
dimensionality is established by the behaviour of the projected pair
distribution function.
