Valleytronic, spintronic, and electronic devices primarily harness the valley, spin, and charge entities of an electron. Our study delves into the merger of these properties in Janus $MX{\mathrm{SiN}}_2$ ($M$ = Cr/Mo/W; $X$ = S/Se/Te) monolayers. Outperforming their pristine $M{\mathrm{Si}}_2{\mathrm{N}}_4$ monolayers, the Janus $MX{\mathrm{SiN}}_2$ monolayers exhibit concurrent vertical and horizontal electric polarization stemming from their unique geometry. The absence of out-of-plane mirror symmetry and inversion symmetry, in addition to strong spin-orbit coupling, leads to in-plane Rashba spin splitting (${\alpha }_R\sim 0.015$–0.624 eV Å), out-of-plane Zeeman-type valley spin splitting (${\mathrm{\Delta }}_{SO}^{c/v}\sim 4-374\mathrm{meV})$, and valley-contrasting Berry curvature (${\mathrm{\Omega }}_n\sim 6.22–13.30{\AA }^2)$ within the Janus $MX{\mathrm{SiN}}_2$ monolayer family. The tweaking of Rashba and valley spin splitting under biaxial strain is intricately influenced by changes in both the macroscopic charge distribution and the microscopic proportion of the atomic orbitals involved. Notably, at the Γ point of the highest valence band, the Rashba coupling is dominantly influenced by the out-of-plane atomic orbitals, while at the $K/K^{\prime }$ point of the highest valence band, the valley spin splitting is primarily controlled by the in-plane atomic orbitals. This work addresses the long-standing confusion of how orbital composition fundamentally influences spin-dependent phenomena. Further, this study identifies suitable Rashba descriptors like planar average potential difference (ΔΦ), the trace of the Born effective charge ($Z^{*}$), and the macroscopic static dielectric constant (${\varepsilon }_{11}$). Moreover, the Janus $MX{\mathrm{SiN}}_2$ monolayers exhibit moderate in-plane $d_{22}\sim 1.40–4.20\mathrm{pm}/\mathrm{V}$ and out-of-plane piezoelectricity $d_{31}\sim 0.16$–0.50 pm/V, governed by the electronegativity-difference ratio. This comprehensive exploration and integration of the valleytronic, spintronic, and piezoelectric properties serve as a foundation for self-sustained spin-based field-effect transistors, valley-coupled spin Hall effect, piezo-spintronics, etc., shaping the landscape of emerging technologies.

Close

PrevNext

View figure in article

• Piezoelectricity
• Rashba coupling
• Spin-orbit coupling
• Spintronics
• Strain
• Valley degrees of freedom
• Valleytronics
• 2-dimensional systems
• Monolayer films
• Density functional calculations