Long-lived electron spins in a modulation doped (100) GaAs quantum well

We have measured $T_1$ 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. $T_1$ lifetimes in excess of 1 microsecond were measured at 1.5 K and 5.5 T, exceeding the typical $T_2^*$ 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.