• Exciton transfer;
  • Anderson localization;
  • Mode-coupling approximation


The motion of a quantum particle in a random potential with short-range fluctuations is analyzed using a generalized mode-coupling approximation. The original theory of Götze was extended by introducing a wave-vector dependent current relaxation kernel. Here we apply the theory to the special case of exciton dynamics in a binary molecular crystal. We find a localization–delocalization transition in three dimensions with a critical exponent of 1 for the inverse localization length. In the intermediate time regime, our theory predicts a region of anomalous diffusion. This can be interpreted as a precursor to localization. At the transition point it leads to the known asymptotic low-frequency behaviour D″(ω) α ω1/3.