  We have shown experimentally that an electric field decreases the energy
separation between the two components of a dense spin-polarized exciton gas in
a coupled double quantum well, from a maximum splitting of $\sim 4$ meV to
zero, at a field of $\sim $35 kV/cm. This decrease, due to the field-induced
deformation of the exciton wavefunction, is explained by an existing
calculation of the change in the spin-dependent exciton-exciton interaction
with the electron-hole separation. However, a new theory that considers the
modification of screening with that separation is needed to account for the
observed dependence on excitation power of the individual energies of the two
exciton components.
