Inverse Rashba–Edelstein Effect (IREE) Overview

• The Inverse Rashba–Edelstein Effect (IREE) is an interfacial phenomenon that converts nonequilibrium spin accumulation or spin currents into a transverse electrical current via Rashba spin–orbit coupling.
• It is experimentally demonstrated in systems like Bi/Ag bilayers and oxide 2DEGs, showing spin-to-charge conversion efficiencies that can rival or exceed the bulk spin Hall effect.
• Theoretical and practical analyses using spin-pumping, lateral spin valves, and Boltzmann-kinetic approaches underpin its role in advancing next-generation spintronic devices and THz emission technologies.

The inverse Rashba–Edelstein effect (IREE) describes the conversion of a nonequilibrium interfacial spin accumulation or spin current into a transverse electrical current, mediated by Rashba-type spin–orbit coupling at interfaces or surfaces lacking inversion symmetry. The IREE is a fundamentally interfacial effect and is central to a variety of spin–charge interconversion phenomena in quantum materials and engineered heterostructures. It is now recognized as a leading mechanism for spin–charge conversion in Rashba interfaces, oxide 2DEGs, topological materials, and two-dimensional chalcogenides, with efficiency rivaling that of the bulk spin Hall effect in heavy metals and frequently exceeding it in atomically engineered systems.

1. Theoretical Formulation and Fundamental Expressions

The IREE emerges in systems where the electronic structure is governed by Rashba spin–orbit coupling (SOC), described by the model Hamiltonian

$$H_R = \alpha_R\, (\boldsymbol{k} \times \hat{\boldsymbol{z}})\cdot\boldsymbol{\sigma}$$

where $\alpha_R$ is the Rashba coupling constant, $\boldsymbol{k}$ the in-plane wavevector, $\hat{\boldsymbol{z}}$ the interface normal, and $\boldsymbol{\sigma}$ the vector of Pauli matrices. This Hamiltonian yields spin-split bands with helical momentum–spin locking in the interfacial plane (Jungfleisch et al., 2015, Shen et al., 2013, Nakayama et al., 2016).

When a nonequilibrium spin accumulation $\boldsymbol{S}$ (or equivalently, a spin-current density $J_s$) is injected into the Rashba interface, the IREE induces a 2D charge current $J_c$ transverse to both the spin polarization and the interface normal: $$J_c = \frac{2e}{\hbar} \lambda_{\rm IREE} (\hat{\boldsymbol{z}} \times \boldsymbol{\sigma})$$ where $\lambda_{\rm IREE}$ is the Edelstein length (spin-to-charge conversion efficiency in nm). The microscopic relation $\alpha_R$0 connects the IREE response to the Rashba parameter $\alpha_R$1 and interfacial spin–momentum relaxation time $\alpha_R$2 (Shen et al., 2013, Jungfleisch et al., 2015).

The IREE is the Onsager reciprocal of the direct Rashba–Edelstein effect (REE), where a charge current induces a non-equilibrium spin accumulation (Shen et al., 2013, Jungfleisch et al., 2015). The associated conversion tensor can be generalized to anisotropic or multi-band systems (Gaiardoni et al., 26 Mar 2025, Song et al., 2021).

2. Experimental Realizations and Measurement Strategies

IREE has been experimentally identified by detecting a lateral charge current or voltage in Rashba interfaces subject to spin injection, with canonical demonstrations including Bi/Ag and Cu/Bi bilayers, transition-metal dichalcogenide heterostructures, oxide 2DEGs, and Weyl semimetals (Jungfleisch et al., 2015, Matsushima et al., 2017, Song et al., 2016, Massabeau et al., 2024, Mendes et al., 2022). Typical measurement protocols include:

• Spin-pumping via ferromagnetic resonance (FMR): A precessing ferromagnet injects a spin current into the interface. The resulting IREE charge current is detected as a dc voltage or as part of a rectified resonance signal (e.g., spin-torque FMR) (Jungfleisch et al., 2015, Matsushima et al., 2017, Mendes et al., 2022).
• Lateral spin valves: A spin-polarized current is injected into a nonmagnetic channel, with the IREE detected as a nonlocal transverse charge signal at the interface (Isasa et al., 2014).
• Optically triggered spin-to-charge conversion: Ultrafast optical excitation injects a spin population, yielding IREE-mediated broadband THz emission in Rashba heterostructures (Zhou et al., 2018, Massabeau et al., 2024).
• Field-effect and ferroelectric modulation: The IREE efficiency can be tuned by electric gating (oxide 2DEGs, TMDs) or by ferroelectric polarization, enabling non-volatile and voltage-controlled modulation (Song et al., 2016, Massabeau et al., 2024).

Considerable care is required to separate IREE currents from bulk (inverse spin Hall) effects and from artifact rectification or thermoelectric signals (Matsushima et al., 2017, Mendes et al., 2022).

3. Quantitative Metrics and Material Benchmarking

IREE efficiency is encapsulated by the Edelstein length $\alpha_R$3, typically extracted by relating the output charge current $\alpha_R$4 to the injected spin current $\alpha_R$5: $\alpha_R$6 Values of $\alpha_R$7 for prototypical systems:

Material/Interface	$\alpha_R$8 (nm)	Reference
Bi/Ag (metallic interface)	0.1–0.3	(Jungfleisch et al., 2015, Matsushima et al., 2017, Shen et al., 2013)
SrTiO$\alpha_R$9/LaAlO$\boldsymbol{k}$0 (oxide 2DEG)	0.6–1.1	(Song et al., 2016)
MoSe$\boldsymbol{k}$1/PtSe$\boldsymbol{k}$2 (TMD/TMD)	0.2–0.3	(Massabeau et al., 2024)
Cu/Bi (semimetallic)	$\boldsymbol{k}$3	(Isasa et al., 2014)
TaP (Weyl semimetal)	0.3	(Mendes et al., 2022)
Monolayer OsBi$\boldsymbol{k}$4 (giant IREE)	2.6–3.2	(Song et al., 2021)

The measured $\boldsymbol{k}$5 is set by interfacial $\boldsymbol{k}$6 and $\boldsymbol{k}$7, but is also strongly affected by interface quality, Fermi level position, and disorder (Zulkoskey et al., 2019, Isasa et al., 2014). Notably, topologically nontrivial and hybridized Rashba systems (e.g., OsBi$\boldsymbol{k}$8) can achieve “giant” IREE, with efficiencies an order of magnitude above classical Rashba systems (Song et al., 2021).

4. Microscopic Mechanisms and Modeling Frameworks

The IREE originates from the conversion between nonequilibrium spin populations and charge currents due to the Rashba SOC-induced spin texture. The underlying mechanisms have been analyzed via:

• Drift–diffusion and SU(2) gauge theories: These yield closed-form relations for the SU(2)-covariant spin and charge continuity equations and define the conversion length $\boldsymbol{k}$9 in terms of $\hat{\boldsymbol{z}}$0, relaxation times, and density of states (Shen et al., 2013).
• Boltzmann-kinetic approaches: Provide explicit solutions for steady-state currents under realistic boundary conditions, supporting self-consistent extraction of $\hat{\boldsymbol{z}}$1 and elucidating parameter dependence on $\hat{\boldsymbol{z}}$2, $\hat{\boldsymbol{z}}$3, and sample dimensions (Gaiardoni et al., 5 Jan 2026, Gaiardoni et al., 26 Mar 2025, Yama et al., 2023).
• Kubo/Bastin response: Enable inclusion of multiband and anisotropic effects, finite temperature, spin textures, and Fermi-level dependencies, and clarify the role of interfacial band hybridization and electron–phonon scattering (Massabeau et al., 2024, Song et al., 2021, Zulkoskey et al., 2019).
• Nonlinear/adiabaticity regimes: At fields or currents beyond linear response, the IREE efficiency can be suppressed by nonadiabatic spin evolution; Onsager reciprocity is retained even in strongly nonlinear regimes (Vignale et al., 2015).

Enhancement mechanisms include band-structure effects (hybridization-induced constructive chirality), interface confinement (density-of-states singularities), and anisotropic effective masses or Rashba couplings (Song et al., 2021, Zulkoskey et al., 2019, Gaiardoni et al., 26 Mar 2025).

5. Distinctions from Related Spin–Charge Conversion Effects

While often compared to the bulk inverse spin Hall effect (ISHE), the IREE is fundamentally distinct in its interfacial nature and symmetry, microscopic origin, and ultrathin spatial extent:

• Location and mechanism: ISHE is a bulk phenomenon relying on band-internal SOC and spin-dependent scattering; IREE is confined to $\hat{\boldsymbol{z}}$4 nm interfacial regions where $\hat{\boldsymbol{z}}$5 is maximized by inversion symmetry breaking (Ovalle et al., 12 Nov 2025, Nakayama et al., 2016).
• Symmetry and sign control: IREE enables sign reversal by stacking/inversion (Bi/Ag vs Ag/Bi), ferroelectric polarization (in TMD/ferroelectric heterostructures), and Fermi-level tuning, impossible in conventional ISHE (Massabeau et al., 2024, Matsushima et al., 2017).
• Physical observables: IREE yields a charge current directly proportional to the interfacial spin accumulation or spin current, rather than its gradient, and dominates over ISHE in thin Rashba systems (Ovalle et al., 12 Nov 2025).
• Enhancement via band hybridization and dimensionality: IREE efficiency can be dramatically increased in systems with nontrivial spin textures or confined density of states, as shown in OsBi$\hat{\boldsymbol{z}}$6 and at Rashba 3D/2D interfaces (Song et al., 2021, Zulkoskey et al., 2019).

6. Technological Implications and Prospects

IREE-based devices have enabled:

• Efficient, low-power spin detection and spin current sources in 2D and interface-based spintronic circuits (Jungfleisch et al., 2015, Song et al., 2016);
• Rectification and THz emission circuitry with gate and ferroelectric control for high-speed communication technology (Massabeau et al., 2024, Zhou et al., 2018);
• Room-temperature operation in oxide, metallic, and Weyl semimetal platforms, greatly expanding integrability and design flexibility (Mendes et al., 2022, Song et al., 2016);
• Design of on-demand, sign-tunable and even non-volatile spin–charge conversion elements by stacking sequence or ferroelectricity (Massabeau et al., 2024, Matsushima et al., 2017).

Limiting factors include interfacial disorder, spin relaxation, and Fermi level positioning; optimal device engineering leverages atomically abrupt interfaces, band-structure design, and electrostatic gating.

7. Open Challenges and Future Directions

Major challenges include:

• Quantitative disentanglement of IREE from parallel ISHE and magnetoresistive artifacts, requiring careful modeling and multi-terminal geometries (Matsushima et al., 2017, Nakayama et al., 2016);
• Unified theoretical frameworks for multi-band, anisotropic, and topological systems, going beyond single-band drift–diffusion;
• Exploration of strong-interaction and low-dimensional regimes, with possible enhancements from moiré superlattices, interfacial superconductivity, and field-tunable coupling (Massabeau et al., 2024);
• Integration with other spin–orbit effects (e.g., orbital–to–charge conversion) and with quantum information protocols.

Continued advances in material synthesis, interface chemistry, and first-principles modeling are anticipated to further enhance the efficiency, controllability, and integration of IREE-based technologies. The effect’s flexibility and robustness position it as a cornerstone mechanism in next-generation spin–orbitronics and THz sources.