Long-Distance Diffusion of Excitons in Double Quantum Well Structures
  In this Letter we report on lateral diffusion measurements of excitons at low temperature in double quantum wells of various widths. The structure is designed so that excitons live up to 30 $\mu$s and diffuse up to 500 $\mu$m. Particular attention is given to establishing that the transport occurs by exciton motion. The deduced exciton diffusion coefficients have a very strong well-width dependence, and obey the same power law as the diffusion coefficient for electrons. 
Z. V\"or\"os, R. Balili, D.W. Snoke, L. Pfeiffer and K. West