  Using an adiabatic approximation we derive an effective interaction
potentially for spatially indirect excitons. Using this potential and path
integral Monte Carlo simulations we study exciton crystllization and the
quantum melting phase transition in a macroscopic system of 2D excitons.
Furthermore, the superfluid fraction is calculated as a function of density and
shown to vanish upon crystallization. We show that the commonly used dipole
model fails to correctly describe indirect excitons in quantum well structures.
