  Charge-to-spin conversion in various material systems is the key for the
fundamental understanding of spin-orbitronis as well as the development of
efficient means to manipulate the magnetization. We report the direct spatial
imaging of current induced spin accumulation at the channel edges of Bi2Se3 and
BiSbTeSe2 topological insulators by a scanning photovoltage microscope at room
temperature. The spin polarization is along the out-of-plane direction with
opposite signs for the two channel edges. The accumulated spin direction
reverses sign upon changing the current direction and the detected spin signal
shows a linear dependence on the magnitude of currents, which indicates that
our observed phenomena are the current induced effects. The spin Hall angle of
Bi2Se3 and BiSbTeSe2 is determined to be 0.0085 and 0.0616, respectively. We
further image the current induced spin accumulation in a Pt heavy metal. Our
results open up the possibility of optically detecting the current induced spin
accumulations, and thus point towards a better understanding of the interaction
between spins and circularly polarized light.
