  Storing, transmitting, and manipulating information using the electron spin
resides at the heart of spintronics. Fundamental for future spintronics
applications is the ability to control spin currents in solid state systems.
Among the different platforms proposed so far, semiconductors with strong
spin-orbit interaction are especially attractive as they promise fast and
scalable spin control with all-electrical protocols. Here we demonstrate both
the generation and measurement of pure spin currents in semiconductor
nanostructures. Generation is purely electrical and mediated by the spin
dynamics in materials with a strong spin-orbit field. Measurement is
accomplished using a spin-to-charge conversion technique, based on the magnetic
field symmetry of easily measurable electrical quantities. Calibrating the
spin-to-charge conversion via the conductance of a quantum point contact, we
quantitatively measure the mesoscopic spin Hall effect in a multiterminal GaAs
dot. We report spin currents of 174 pA, corresponding to a spin Hall angle of
34%.
