Charge-to-spin conversion and spin diffusion in Bi/Ag bilayers observed by spin-polarized positron beam

Zhang, H. J.; Yamamoto, Shunya; Gu, B.; Li, H.; Maekawa, Masaki; Fukaya, Yuki   ; Kawasuso, Atsuo

Charge-to-spin conversion induced by the Rashba-Edelstein effect was directly observed for the first time in samples with no magnetic layer. A spin-polarized positron beam was used to probe the spin polarization of the outermost surface electrons of Bi/Ag/AlO and Ag/Bi/AlO when charge currents were only associated with the Ag layers. An opposite surface spin polarization was found between Bi/Ag/AlO and Ag/Bi/AlO samples with the application of a charge current in the same direction. The surface spin polarizations of both systems decreased exponentially with the outermost layer thickness, suggesting the occurrence of spin diffusion from the Bi/Ag interface to the outermost surfaces. This work provides a new technique to measure spin diffusion length.