  We have measured T1 spin lifetimes of a 14 nm modulation-doped (100) GaAs
quantum well using a time-resolved pump-probe Kerr rotation technique. The
quantum well was selected by tuning the wavelength of the probe laser. T1
lifetimes in excess of 1 microsecond were measured at 1.5 K and 5.5 T,
exceeding the typical T2* lifetimes that have been measured in GaAs and II-VI
quantum wells by orders of magnitude. We observed effects from nuclear
polarization, which were largely removable by simultaneous nuclear magnetic
resonance, along with two distinct lifetimes under some conditions that likely
result from probing two differently-localized subsets of electrons.
