Quantum diffusion of dipole-oriented indirect excitons in coupled quantum wells

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.