In this contribution, we investigated the spin coherence of high-mobility dense two-dimensional electron gases confined in multilayer systems. The dynamics of optically-induced spin polarization was experimentally studied employing the time-resolved Kerr rotation and resonant spin amplification techniques. For both the double and triple quantum wells doped beyond the metal-insulator transition, where the spin coherence is greatly suppressed, we found remarkably long spin lifetimes limited by the Dyakonov-Perel mechanism and spin hopping process between the donor sites as well as the spread of ensemble g-factor. The double quantum well structure yields a spin lifetime of 6.25 ns at T = 5 K while the triple quantum well shows a spin lifetime exceeding 25 ns at T = 8 K.
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