  We report experimental results of the effect of Ka-band microwave on the spin
dynamics of electrons in a 2D electron system in a GaAs/Al0.35Ga0.65As
heterostructure, via time-resolved Kerr rotation measurements. While the
microwave reduces the transverse spin lifetime of the bulk GaAs when its
frequency is close to the Zeeman splitting of the electrons in the magnetic
field, it significantly increases that of electrons in the 2D electron system,
from 745 ps to 1213 ps. Such a microwave-enhanced spin lifetime is ascribed to
the microwave-induced electron scattering which leads to a motional narrowing
of spins via DP mechanism.
