  The Edelstein effect caused by the pristine surface states of
three-dimensional topological insulators is investigated by means of a
semiclassical approach. The combined effect of random impurity scattering and
the spin-momentum locking of the gapless Dirac cone yields a current-induced
surface spin accumulation independent from chemical potential and temperature.
Through combing the semiclassical approach with the Bloch equation, the inverse
Edelstein effect that converts the spin pumping spin current into a charge
current is well explained. Consistency of these results with various
experiments will be elaborated in detail.
