Is diffusion anomalous in two-dimensional Yukawa liquids?

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There have recently been many predictions of "superdiffusion" in two-dimensional strongly coupled Yukawa systems, both by computer simulations and in dusty plasma experiments, with substantially varying diffusion exponents. Here we show that the results crucially depend on the strength of dissipation and the time instant of the measurement. For sufficiently large friction even subdiffusion is possible. However, there are strong indications that, in the long-time limit, anomalous diffusion vanishes for dissipative as well as for frictionless systems.