  This paper discusses the combined effects of optical excitation power,
interface roughness, lattice temperature, and applied magnetic fields on the
spin-coherence of excitonic states in GaAs/AlGaAs multiple quantum wells. For
low optical powers, at lattice temperatures between 4 K and 50 K, the
scattering with acoustic phonons and short-range interactions appear as the
main decoherence mechanisms. Statistical fluctuations of the band-gap however
become also relevant in this regime and we were able to deconvolute them from
the decoherence contributions. The circularly polarized
magneto-photoluminescence unveils a non-monotonic tuning of the coherence for
one of the spin components at low magnetic fields. This effect has been
ascribed to the competition between short-range interactions and spin-flip
scattering, modulated by the momentum relaxation time.
