Unveiling the spin-to-charge current conversion signal in the topological insulator <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Bi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Se</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math> by means of spin pumping experiments
J. B. S. Mendes, M. Gamino, R. O. Cunha, J. E. Abrão, S. M. Rezende, A. Azevedo
Abstract
We report an investigation of the spin-to-charge current conversion in sputter-deposited films of the topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ onto single crystalline layers of yttrium iron garnet (YIG-${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$) and polycrystalline films of permalloy ($\mathrm{Py}\text{\ensuremath{-}}{\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$). Pure spin current was injected into the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ layer by means of the spin pumping process produced by the spin precession in microwave driven ferromagnetic resonance of the ferromagnetic film. The spin-to-charge current conversion occurring at the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$/ferromagnet interface is attributed to the inverse Rashba-Edelstein effect (IREE). From the data, we verified that the voltage generated by the spin-to-charge current conversion process in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ has the same polarity as the inverse spin Hall effect in Ta, which is opposite to the one in Pt. Also, from the dependence of the voltage on the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ thickness we were able the to calculate the IREE length values and found that $1.2\phantom{\rule{0.16em}{0ex}}\mathrm{pm}\ensuremath{\le}|{\ensuremath{\lambda}}_{\mathrm{IREE}}|\ensuremath{\le}2.2\phantom{\rule{0.16em}{0ex}}\mathrm{pm}$. This result allows us to conclude that indeed the surface states of ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ have a dominant role in the spin-to-charge current conversion process, and the mechanism based on the spin diffusion process plays a secondary role.