  The finite spin lifetime in solids is often considered a major hindrance for
the development of spintronic devices, which typically require cryogenic
temperatures to mitigate this phenomenon. In this work we show that this
feature can instead be exploited to realize a scheme where spin transport is
modulated at room temperature by a modest electric field. A field directed
antiparallel (parallel) to the spin-diffusion velocity can in fact largely
increase (decrease) the spin-transport length compared with the zero field
case. We find that applying an electric field E = 24 V/cm along a 40 mm-long
path in germanium results in about one order of magnitude modulation of the
spin-polarized electrons entering in the detector. The present work
demonstrates that electric fields can be exploited for guiding spins over
macroscopic distances and for realizing fast, room temperature modulation of
spin accumulation.
