  Drift-diffusion theory - which fully describes charge transport in
semiconductors - is also universally used to model transport of spin-polarized
electrons in the presence of longitudinal electric fields. By transforming spin
transit time into spin orientation with precession (a technique called the
"Larmor clock") in current-sensing vertical-transport intrinsic Si devices, we
show that spin diffusion (and concomitant spin dephasing) can be greatly
enhanced with respect to charge diffusion, in direct contrast to predictions of
spin Coulomb-drag diffusion suppression.
