  We investigate the intersubband spin-density-excitation spectrum of a double
quantum well in a low-density symmetry-broken phase with interwell
antiferromagnetic correlations. This spectrum is related to the intensity
measured in depolarized inelastic light scattering (ILS) experiments and
therefore provides a means of empirically identifying the antiferromagnetic
phase. Our computations reveal the existence of two collective modes, a damped
Nambu-Goldstone (NG) mode arising from the broken spin symmetry and an undamped
optical mode. Since the NG mode contains most of the spectral weight, ILS
experiments will need to examine the low-frequency response for signatures of
the antiferromagnetic phase.
