Coupled Spin-Valley, Rashba Effect, and Hidden Spin Polarization in WSi₂N₄ Family

Using first-principles calculations, we report the electronic properties with a special focus on the band splitting in the WSi₂N₄ class of materials. Due to the broken inversion symmetry and strong spin-orbit coupling, 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 Γ and M points, respectively. The in-plane mirror symmetry (σ) and reduced symmetry of the arbitrary -point, enforce the persistent spin textures (PST) to occur in full BZ. We induce the Rashba splitting by breaking the σ 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. Low energy models demonstrate that the PST along the M-K line is robust to EEF and layer thickness, making them suitable for applications in spintronics and valleytronics.