  Electron spin dynamics are studied in Ga-doped ZnO single crystals by
time-resolved Faraday and Kerr rotation spectroscopies. Long-lived spin
coherence with two dephasing processes is discovered where the characteristic
time is up to 5.2 ns at room temperature. Through the dependence measurements
of laser wavelength and temperature, the room-temperature long-lived spin
signal is attributed to localized electrons. The spin dephasing (relaxation)
processes are independent of transverse (longitudinal) magnetic fields,
indicating the spin dephasing not resulting from the g-factor inhomogeneity and
electron-nuclear hyperfine interaction. It reveals that the two spin dephasing
processes originate from two types of localized electrons, both of which are
dominated by the anisotropic exchange Dzyaloshinskii-Moriya interaction between
adjacent localized electrons.
