Manipulation of the large Rashba spin splitting in polar two-dimensional transition metal dichalcogenides (1606.07985v2)

Abstract: Transition metal dichalcogenide (TMD) monolayers MXY (M=Mo, W, X(not equal to)Y=S, Se, Te) are two-dimensional polar semiconductors. Setting WSeTe monolayer as an example and using density functional theory calculations, we investigate the manipulation of Rashba spin orbit coupling (SOC) in the MXY monolayer. It is found that the intrinsic out-of-plane electric field due to the mirror symmetry breaking induces the large Rashba spin splitting around the Gamma point, which, however, can be easily tuned by applying the in-plane biaxial strain. Through a relatively small strain (from -2% to 2%), a large tunability (from around -50% to 50%) of Rashba SOC can be obtained due to the modified orbital overlap, which can in turn modulate the intrinsic electric field. The orbital selective external potential method further confirms the significance of the orbital overlap between W-dz2 and Se-pz in Rashba SOC. In addition, we also explore the influence of the external electric field on Rashba SOC in the WSeTe monolayer, which is less effective than strain. The large Rashba spin splitting, together with the valley spin splitting in MXY monolayers may make a special contribution to semiconductor spintronics and valleytronics.

Rashba Spin Orbit Coupling Tunability in MXY Monolayers: A Case Study on WSeTe

The paper "Manipulation of the large Rashba spin splitting in polar two-dimensional transition metal dichalcogenides" investigates the modulation of Rashba spin orbit coupling (SOC) in polar two-dimensional transition metal dichalcogenides (TMDs) with a focus on the WSeTe monolayer. Utilizing density functional theory (DFT) calculations, the authors explore how varying biaxial strain and external electric fields affect the intrinsic Rashba SOC, with implications for semiconductor spintronics and valleytronics.

Rashba SOC in MXY Monolayers

TMD monolayers comprising transition metals (M = Mo, W) and chalcogen atoms (X ≠ Y = S, Se, Te), denoted as MXY, exhibit unique electronic and spin properties. These materials inherently lack inversion symmetry, inducing significant SOC effects that are essential for applications in spintronic devices. The authors particularly focus on Rashba SOC, which arises from the structural inversion asymmetry and out-of-plane electric fields in these monolayers, providing an additional tuning mechanism for SOC through external stimuli.

Numerical and Theoretical Insights

1. Intrinsic Electric Field and Rashba SOC: The paper finds that the intrinsic out-of-plane electric field, a result of mirror symmetry breaking in WSeTe, gives rise to notable Rashba SOC around the Γ point. This intrinsic field can be modulated by mechanical deformations like biaxial strain, affecting the electronic and spin structure of the monolayer.
2. Biaxial Strain Effects: The application of small biaxial strains (ranging from -2% to 2%) exhibits considerable tunability of the Rashba SOC (approximately ±50%). This effect is primarily due to the way strain alters orbital overlaps—especially between W-dz² and Se-pz orbitals—thereby influencing the intrinsic electric field and subsequently the SOC. This tunability could be particularly advantageous for tailoring spintronic device functionalities.
3. Role of Orbital Overlaps: Employing the orbital selective external potential (OSEP) method, the authors underscore the significance of orbital overlap modification in SOC manipulation. Adjusting the energy levels of W-dz² orbitals directly affects Rashba SOC, emphasizing that targeted electronic modifications can tailor spin properties effectively.
4. Comparison with Electric Field Influence: The paper also examines the impact of external electric fields on Rashba SOC. Unlike biaxial strains, electric fields have minimal influence on SOC due to the screening effect, primarily affecting surface states rather than deeper atomic states, particularly the W atom's d-orbitals.

Implications and Future Directions

The work significantly enhances the understanding of Rashba SOC modulation in TMD monolayers, proposing avenues for fine-tuning spintronic device properties through mechanical and electrical controls. While the demonstrated strain-induced tunability is substantial, further investigation into other TMD compositions could reveal new materials with even more prominent effects, broadening the practical applications within spintronic and valleytronic devices.

Conclusion

The paper provides a comprehensive analysis of the Rasbha SOC tunability in WSeTe monolayers, highlighting the role of mechanical strain and intrinsic electric fields. By demonstrating substantial Rashba SOC modulation, this research paves the way for future explorations into TMD-based devices with enhanced spintronic functionality, thereby contributing to the broader field of semiconductor device engineering.