  Detection and manipulation of electrons' spins are key prerequisites for
spin-based electronics or spintronics. This is usually achieved by contacting
ferromagnets with metals or semiconductors, in which the relaxation of spins
due to spin-orbit coupling limits both the efficiency and the length scale. In
topological insulator materials, on the contrary, the spin-orbit coupling is so
strong that the spin direction uniquely determines the current direction, which
allows us to conceive a whole new scheme for spin detection and manipulation.
Nevertheless, even the most basic process, the spin injection into a
topological insulator from a ferromagnet, has not yet been demonstrated. Here
we report successful spin injection into the surface states of topological
insulators by using a spin pumping technique. By measuring the voltage that
shows up across the samples as a result of spin pumping, we demonstrate that a
spin-electricity conversion effect takes place in the surface states of
bulk-insulating topological insulators Bi1.5Sb0.5Te1.7Se1.3 and Sn-doped
Bi2Te2Se. In this process, due to the two-dimensional nature of the surface
state, there is no spin current along the perpendicular direction. Hence, the
mechanism of this phenomenon is different from the inverse spin Hall effect and
even predicts perfect conversion between spin and electricity at room
temperature. The present results reveal a great advantage of topological
insulators as inborn spintronics devices.
