  When an electric current passes across a potential barrier, the partition
process of electrons at the barrier gives rise to the shot noise, reflecting
the discrete nature of the electric charge. Here we report the observation of
excess shot noise connected with a spin current which is induced by a
nonequilibrium spin accumulation in an all-semiconductor lateral spin-valve
device. We find that this excess shot noise is proportional to the spin
current. Additionally, we determine quantitatively the spin-injection-induced
electron temperature by measuring the current noise. Our experiments show that
spin accumulation driven shot noise provides a novel means of investigating
nonequilibrium spin transport.
