  A model for diffusion of statistically-degenerate excitons in (coupled)
quantum wells is proposed and analysed. Within a microscopic approach, we
derive a quantum diffusion equation, calculate and estimate the self-diffusion
coefficient for excitons in quantum wells and derive a modified Einstein
relation adapted to statistically-degenerated quasi-two-dimensional bosons. It
is also shown that the dipole-dipole interaction of indirect excitons
effectively screens long-range-correlated disorder in quantum wells. Numerical
calculations are given for indirect excitons in GaAs/AlGaAs coupled quantum
wells.
