EXCITONS IN HIGH MAGNETIC-FIELDS IN DISORDERED 2-DIMENSIONAL SYSTEMS - WEAK-LOCALIZATION EFFECTS FOR COMPOSITE NEUTRAL PARTICLES

Quantum corrections to transport of two-dimensional (2D) excitons are considered in high magnetic fields. We find that despite total charge neutrality of these composite particles, there is no weak localization and the diffusion constant remains finite even without inelastic phase-breaking processes. This is due to time-reversal symmetry breaking by the magnetic field B. (The only exception is the case when the electron and hole components are exact t-->-t counterparts; then 2D excitons are always localized in B.) Nevertheless, weak localization corrections change significantly the dependence of the diffusion constant D(B), leading in high fields to much faster decrease of D with B in comparison with classical transport.