Giant inverse Rashba-Edelstein effect: Application to monolayer OsBi2

We propose that the hybridization between two sets of Rashba bands can lead to the unconventional Rashba band structures where the two Fermi circles from different bands own in-plane helical spin textures with the same chiralities, and possess group velocities with the same directions. Through the first-principles calculations, we predict that monolayer ${\mathrm{OsBi}}_{2}$ hosts such simple and pure unconventional Rashba bands near Fermi energy. Under the weak spin injection, we show that the two Fermi circles from the unconventional Rashba bands both give the positive contributions to the spin-to-charge conversion and thus induce the giant inverse Rashba-Edelstein Effect with large conversion efficiency, which is very different from the conventional Rashba-Edelstein Effect. Our studies not only provide a promising material of monolayer ${\mathrm{OsBi}}_{2}$ to possess unconventional Rashba bands, but also demonstrate its potential application to achieve highly efficient spin-to-charge conversion in spintronics.