  Uniaxial compressive strain along the [001] direction strongly suppresses the
spin relaxation in silicon. When the strain level is large enough so that
electrons are redistributed only in the two valleys along the strain axis, the
dominant scattering mechanisms are quenched and electrons mainly experience
intra-axis scattering processes (intravalley or intervalley scattering within
valleys on the same crystal axis). We first derive the spin-flip matrix
elements due to intra-axis electron scattering off impurities, and then provide
a comprehensive model of the spin relaxation time due to all possible
interactions of conduction-band electrons with impurities and phonons. We
predict nearly three orders of magnitude improvement in the spin relaxation
time of $\sim10^{19}\text{cm}^{-3}$ antimony-doped silicon (Si:Sb) at low
temperatures.
