  We report an investigation of the spin- to charge-current conversion in
sputter-deposited films of topological insulator $Bi_2Se_{3}$ onto single
crystalline layers of YIG $(Y_{3}Fe_{5}O_{12})$ and polycrystalline films of
Permalloy $(Py = Ni_{81}Fe_{19})$. Pure spin current was injected into the
$Bi_{2}Se_{3}$ layer by means of the spin pumping process in which the spin
precession is obtained by exciting the ferromagnetic resonance of the
ferromagnetic film. The spin-current to charge-current conversion, occurring at
the $Bi_{2}Se_{3}/$ferromagnet interface, was attribute to the inverse
Rashba-Edelstein effect (IREE). By analyzing the data as a function of the
$Bi_{2}Se_{3}$ thickness we calculated the IREE length used to characterize the
efficiency of the conversion process and found that 1.2 pm
$\leq|{\lambda}_{IREE}|\leq$ 2.2 pm. These results support the fact that the
surface states of $Bi_{2}Se_{3}$ have a dominant role in the spin-charge
conversion process, and the mechanism based on the spin diffusion process plays
a secondary role. We also discovered that the spin- to charge-current mechanism
in $Bi_{2}Se_{3}$ has the same polarity as the one in Ta, which is the opposite
to the one in Pt. The combination of the magnetic properties of YIG and Py,
with strong spin-orbit coupling and dissipationless surface states
topologically protected of $Bi_{2}Se_{3}$ might lead to spintronic devices with
fast and efficient spin-charge conversion.
