Collinear Rashba-Edelstein effect in nonmagnetic chiral materials

Efficient generation and manipulation of spin signals in a given material without invoking external magnetism remain one of the challenges in spintronics. The spin Hall effect (SHE) and Rashba-Edelstein effect (REE) are well-known mechanisms to electrically generate spin accumulation in materials with strong spin-orbit coupling (SOC), but the exact role of the strength and type of SOC, especially in crystals with low symmetry, has yet to be explained. In this study, we investigate REE in three different families of nonmagnetic chiral materials, elemental semiconductors (Te and Se), metal silicides (FeSi and OsSi), and semimetal disilicides (TaSi2 and NbSi2), using an approach based on density functional theory. By analyzing spin textures across the full Brillouin zones and comparing them with REE magnitudes calculated as a function of chemical potential, we link specific features in the electronic structure with the efficiency of the induced spin accumulation. Our findings show that magnitudes of REE can be increased by (i) the presence of one particular type of spin-orbit field, for example, Weyl-type SOC that yields a radial spin texture, (ii) high spin polarization of bands along one specific crystallographic direction, and (iii) low band velocities. By comparing materials possessing the same crystal structures but different strengths of SOC, we conclude that larger SOC may indirectly contribute to the enhancement of REE. It yields greater spin splitting of bands along specific crystallographic directions, which prevents canceling the contributions from the oppositely spin-polarized bands over wider energy regions and helps maintain larger REE magnitudes. Surprisingly, however, for some materials, the velocity of electronic states plays an even more important role in regulating the REE magnitudes than SOC. Additionally, these magnitudes are strongly influenced by changes in band topology. We believe that our results will be useful for designing spintronics devices and may aid further computational studies searching for efficient REE in materials with different symmetries and SOC strengths.