How can we electrically detect spin current? In 1918, Schottky argued that the electric flow in a vacuum tube shows peculiar fluctuation whose amplitude is proportional to elementary charge and to the mean current. This is shot noise, a direct consequence of the discreteness of the electric charge. Now, consider the discreteness of spin. By using a spin-valve-type solid-state device, we successfully detected the shot noise induced by a　non-equilibrium spin accumulation. The observed shot noise is proportional to the spin current, yielding a spin analogue of Schottky’s argument. Our experimental demonstration could open a novel way to approach non-equilibrium spin phenomena like spintronics.

Schematic diagram of the measurement system.
By applying a constant current to a ferromagnetic (Ga,Mn)As electrode, we inject spin polarized electrons into the n-GaAs channel. As a result, a spin current is generated and flow into another ferromagnetic electrode. This spin current lead to a current fluctuation through the tunnel junction.

(Link) http://resou.osaka-u.ac.jp/en/research/2015/20150122_1