The Stokes-Einstein relation, relating the diffusion and viscosity coefficients $D$ and $\eta$, is tested in two dimensions. An equilibrium molecular-dynamics simulation was used with a Yukawa pair potential. Regimes are identified where motion is diffusive and $D$ is meaningful. The Stokes-Einstein relation, $D\eta \propto k_{B}T$, was found to be violated near the disordering transition; under these conditions collective particle motion exhibits dynamical heterogeneity. At slightly higher temperatures, however, the Stokes-Einstein relation is valid. These results may be testable in strongly coupled dusty plasma experiments.

• Received 9 August 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.015005