  We report observation of intrinsic inverse spin Hall effect in un-doped GaAs
multiple quantum wells with a sample temperature of 10 K. A transient ballistic
pure spin current is injected by a pair of laser pulses through quantum
interference. By time-resolving the dynamics of the pure spin current, the
momentum relaxation time is deduced, which sets the lower limit of the
scattering time between electrons and holes. The transverse charge current
generated by the pure spin current via the inverse spin Hall effect is
simultaneously resolved. We find that the charge current is generated well
before the first electron-hole scattering event. Generation of the transverse
current in the scattering-free ballistic transport regime provides unambiguous
evidence for the intrinsic inverse spin Hall effect.
