First-principles study on Giant Hidden Rashba Effects in novel Two-Dimensional Si₂Bi₂

In contrast to the general view in spin-orbit interaction, it was reported that even in materials with centrosymmetry may have hidden Rashba spin-orbit coupling (the R-2 effect) resulting in spatial spin splitting. However, not only its underlying fundamental physics been still unclear, but the search for materials exhibiting the R-2 interaction has also been very limited. Here, through first-principles density functional theory and model Hamiltonian calculations, we investigate giant spin-layer locking observed in novel two-dimensional materials Si₂Bi₂. The local symmetry breaking produces opposite out-of-plane dipole moments at the top and bottom atomic sublayers leading to the R-2 spin layer locking as well as hidden orbital Rashba effects. Interestingly, we further reveal that the competition between the sublayer-sublayer interaction and the spin-orbit coupling plays a crucial role in determining the R-2 spin layer locking.