Coupled spin-valley, Rashba effect and hidden persistent spin polarization in WSi${}_2$N${}_4$ family

Abstract

The new two-dimensional materials, MoSi${}_2$N${}_4$ and WSi${}_2$N${}_4$ are experimentally synthesized successfully and various similar structures are predicted theoretically. Here, we report the electronic properties with a special focus on the band splitting in WA${}_2$Z${}_4$ (A=Si, Ge; Z=N, P, As), using state-of-the-art density functional theory and many-body perturbation theory (within the framework of G${}_0$W${}_0$ and BSE). Due to the broken inversion symmetry and strong spin-orbit coupling effects, we detect coupled spin-valley effects at the corners of the first Brillouin zone (BZ). Additionally, we observe cubically and linearly split bands around the $\Gamma$ and M points, respectively. Interestingly, the in-plane mirror symmetry (${\sigma }_h$) and the reduced symmetry of arbitrary $k$-point, enforce the persistent spin textures (PST) to occur in full BZ. We induce the Rashba splitting by breaking the ${\sigma }_h$ through an out-of-plane external electric field (EEF). The inversion asymmetric site point group of the W atom introduces the hidden spin polarization in centrosymmetric layered bulk counterparts. Therefore, the spin-layer locking effect, namely, energy degenerate opposite spins spatially segregated in the top and bottom W layers, has been identified. Our low energy $k.p$ model demonstrates that the PST along the M-K line is robust to EEF and layer thickness, making them suitable for applications in spintronics and valleytronics.

References in corpus (8)

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• An Exact SU(2) Symmetry and Persistent Spin Helix in a Spin-Orbit Coupled System
• Uncovering and tailoring hidden Rashba spin-orbit splitting in centrosymmetric crystals
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• Defect-induced large spin-orbit splitting in the monolayer of PtSe${}_2$
• Origin of Rashba spin-splitting and strain tunability in ferroelectric bulk CsPbF${}_3$
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Cited by in corpus (6)

• Emergence of Rashba splitting and spin-valley properties in Janus MoGeSiP2As2 and WGeSiP2As2 monolayers
• Manipulation of valley and spin properties in two-dimensional Janus WSiGeZ${}_4$ (Z=N,P, As) through symmetry control
• Probing the uniaxial strain-dependent valley drift and Berry curvature in monolayer MoSi${}_2$N${}_4$
• Correlation-driven topological transition in Janus VSiGeP2As2
• Emergence of Rashba spin valley state in two-dimensional strained bismuth oxychalcogenides Bi${}_2$O${}_2$Se
• (110) Facet of MgTe Zinc Blende Semiconductor: A Holy Grail for Modern Spintronics