  We propose that the hybridization between two sets of Rashba bands can lead
to an unconventional topology 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. Under the weak spin injection, the two
Fermi circles 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. More importantly, through the first-principles
calculations, we predict that monolayer OsBi2 could be a good candidate to
realize the giant inverse Rashba-Edelstein Effect. Our studies not only
demonstrate a new mechanism to achieve highly efficient spin-to-charge
conversion in spintronics, but also provide a promising material to realize it.
