Interface Transparency and Rashba Spin Torque Enhancement in WSe₂ Heterostructures

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Rashba spin current generation is crucial for spintronics, typically occurring at interfaces between ferromagnets and transition metal dichalcogenides (TMDs) due to broken inversion symmetry.
• Epitaxial films on 2D materials can exhibit transparency, where substrate interface effects are not fully screened, but this hasn't been explored for Rashba effects.
• Spin-orbit torque (SOT) is a key phenomenon in spintronics, enabling manipulation of magnetic states via spin currents.

Purpose of the Study:

• To investigate the effect of inserting low layer count tungsten diselenide (WSe2) films on Rashba spin current generation and spin transfer torques in ferromagnet heterostructures.
• To determine if the transparency effect observed in 2D material heterostructures can enhance interfacial phenomena like Rashba spin-orbit torques.
• To explore the potential of WSe2 as an interfacial 'scattering promoter' without negatively impacting interface polarization.

Main Methods:

• Fabrication of heterostructures comprising permalloy (Py) and varying layers (up to two monolayers) of WSe2.
• Measurement and characterization of spin transfer torques and spin-orbit torques (SOT) in these engineered heterostructures.
• Analysis of the impact of WSe2 insertion on interface polarization and spin current generation efficiency.

Main Results:

• Insertion of up to two monolayers of WSe2 into Py heterostructures resulted in a significant enhancement of spin transfer torques by up to 3 times.
• The fieldlike Rashba spin-orbit torque (SOT), indicative of interface polarization, remained unchanged after WSe2 insertion.
• Low layer count WSe2 films acted as effective 'scattering promoters' at the interface, enhancing spin torque without quenching the inherent polarization.

Conclusions:

• Low layer count transition metal dichalcogenides, specifically WSe2, can be utilized to enhance spin transfer torques in Rashba systems.
• The observed enhancement is attributed to WSe2's role as an interfacial scattering promoter, boosting spin torque efficiency without compromising interface polarization.
• These findings open new possibilities for designing advanced spintronic devices by leveraging interfacial engineering in 2D material heterostructures.