Rashba–Edelstein effect

The Rashba–Edelstein effect (REE) is a spintronics-related effect, consisting in the conversion of a bidimensional charge current into a spin accumulation. This effect is an intrinsic charge-to-spin conversion mechanism and it was predicted in 1990 by the scientist V.M. Edelstein. It has been demonstrated in 2013 and confirmed by several experimental evidences in the following years..

Not to be confused with the Bychkov–Rashba effect, sometimes also known as the Rashba effect.

Its origin can be ascribed to the presence of spin-polarized surface or interface states. Indeed, a structural inversion symmetry breaking (i.e., a structural inversion asymmetry (SIA)) causes the Rashba effect to occur: this effect breaks the spin degeneracy of the energy bands and it causes the spin polarization being locked to the momentum in each branch of the dispersion relation. If a charge current flows in these spin-polarized surface states, it generates a spin accumulation. In the case of a bidimensional Rashba gas, where this band splitting occurs, this effect is called Rashba–Edelstein effect.

For what concerns a class of peculiar materials, called topological insulators (TI), spin-splitted surface states exist due to the surface topology, independently from the Rashba effect. Topological insulators, indeed, display a spin-splitted linear dispersion relation on their surfaces (i.e., spin-polarized Dirac cones), while having a band gap in the bulk (this is why these materials are called insulators). Also in this case, spin and momentum are locked and, when a charge current flows in these spin-polarized surface states, a spin accumulation is produced and this effect is called Edelstein effect. In both cases, a 2D charge-to-spin conversion mechanism occurs.

The reverse process is called inverse Rashba–Edelstein effect and it converts a spin accumulation into a bidimensional charge current, resulting in a 2D spin-to-charge conversion.

The Rashba–Edelstein effect and its inverse effect are classified as a spin-charge interconversion (SCI) mechanisms, as the direct and inverse spin Hall effect, and materials displaying these effects are promising candidate for becoming spin injectors, detectors and for other future technological applications.

The Rashba–Edelstein effect is a surface effect, at variance with the spin Hall effect which is a bulk effect. Another difference among the two, is that the Rashba–Edelstein effect is a purely intrinsic mechanism, while the spin Hall effect origin can be either intrinsic or extrinsic.

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