Highly efficient and tuneable spin-to-charge conversion through Rashba coupling at oxide interfaces (1609.06464v1)

Abstract: The spin-orbit interaction couples the electrons' motion to their spin. Accordingly, passing a current in a material with strong spin-orbit coupling generates a transverse spin current (spin Hall effect, SHE) and vice-versa (inverse spin Hall effect, ISHE). The emergence of SHE and ISHE as charge-to-spin interconversion mechanisms offers a variety of novel spintronics functionalities and devices, some of which do not require any ferromagnetic material. However, the interconversion efficiency of SHE and ISHE (spin Hall angle) is a bulk property that rarely exceeds ten percent, and does not take advantage of interfacial and low-dimensional effects otherwise ubiquitous in spintronics hetero- and mesostructures. Here, we make use of an interface-driven spin-orbit coupling mechanism - the Rashba effect - in the oxide two-dimensional electron system (2DES) LaAlO3/SrTiO3 to achieve spin-to-charge conversion with unprecedented efficiency. Through spin-pumping, we inject a spin current from a NiFe film into the oxide 2DES and detect the resulting charge current, which can be strongly modulated by a gate voltage. We discuss the amplitude of the effect and its gate dependence on the basis of the electronic structure of the 2DES.

• The paper demonstrates a tunable Rashba-induced inverse Edelstein effect that yields >10× spin-to-charge conversion efficiency over conventional methods.
• It employs advanced interface engineering via pulsed laser deposition and sputtering to create high-quality LAO/STO heterostructures with gate-voltage control.
• Temperature-dependent spin-pumping experiments at 7 K confirm the pivotal role of Rashba spin-orbit interactions in enabling robust spin-to-charge conversion.

Insights into Spin-to-Charge Conversion via Rashba Coupling at Oxide Interfaces

This paper investigates a novel approach to spin-to-charge conversion utilizing Rashba interactions at oxide interfaces. The paper focuses on utilizing two-dimensional electron systems (2DES) at LaAlO$_3$/SrTiO$_3$ (LAO/STO) interfaces to achieve superior conversion efficiency, leveraging the interface-driven Rashba effect. The objective is to demonstrate a significant increase in spin-to-charge conversion efficiency compared to traditional mechanisms such as the spin Hall effect (SHE).

Spin-orbit interactions (SOI) are instrumental in the conversion processes between spin and charge currents. While conventional SHE does not commonly exceed a 10% conversion efficiency, this research showcases a conversion efficiency at the LAO/STO interface that is more than an order of magnitude higher than previously reported values. A key novelty is the tunability of this efficiency via an applied gate voltage, facilitating control over the interfacial electronic structure and thereby modulating the spin-to-charge conversion properties.

Key Findings

1. Enhanced Efficiency: The reported inverse Edelstein effect (IEE) at the NiFe/LAO//STO interface displays a conversion efficiency far exceeding traditional systems, with a significant order of magnitude improvement compared to both SHE and existing Rashba interface systems such as Ag/Bi(111).
2. Interface Engineering: By employing a combination of pulsed laser deposition and sputtering techniques, the paper demonstrates effective formation of a high-quality 2DES with modifiable conversion efficiency through gate voltage application.
3. Temperature-Dependent Experiments: Spin-pumping experiments at low temperatures (7 K) highlight a clear spin-to-charge conversion signal, confirming the role of Rashba-induced IEE at the interface.
4. Gate-Voltage Modulation: The paper reveals that the conversion efficiency can be adjusted over more than an order of magnitude by applying a back-gate voltage, demonstrating a crossover in signal polarity with varying electron band occupancy levels at different dielectric constants and carrier densities.

Implications and Future Directions

The results emphasize the potential of oxide interfaces, specifically LAO/STO heterostructures, as rich platforms for spintronic applications. These interfaces offer possibilities beyond what ferromagnetic materials provide, by allowing for efficient modulation of spin transport properties using electric fields. Their robust spin-to-charge conversion capabilities can be exploited in the design of novel spin-based devices, possibly leading to advancements in low-power electronics and data storage solutions.

Future research should continue to explore other oxide interfaces and their underlying electronic structures to harness diverse spin-orbit interaction effects. Additionally, combining these interface systems with topological insulators could further amplify their spintronic functionalities, opening avenues for unprecedented device architectures. The theoretical exploration of multiband interactions and their spin-momentum locking properties also holds promise for refining the control and predictability of spin transport in such systems.

Overall, this paper provides a thorough examination of Rashba spin-orbit interactions at oxide interfaces, offering a valuable contribution to the field of spintronics with potential for broad applications in next-generation electronic devices.