Origin of Rashba-Dresselhaus effect in the ferroelectric nitride perovskite LaWN3

First-principles electronic-structure calculations have been employed to investigate the Rashba-Dresselhaus spin splitting of bands in the recently predicted ferroelectric nitride perovskite ${\mathrm{LaWN}}_{3}$. Our first-principles results are supplemented with an effective $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ model analysis. A systematic study of orthorhombic and rhombohedral phases of this system reveals the importance of symmetry in realizing the nature of the splitting of bands around the time-reversal invariant $k$ points. Orthorhombic ${\mathrm{LaWN}}_{3}$ shows linear Rashba-Dresselhaus splitting where nonsymmorphic symmetries play an important role in enhancing the band splitting in the ${k}_{z}=\ensuremath{\pi}/c$ plane, while the rhombohedral phase shows the existence of a unique higher order Rashba-Dresselhaus term which mixes with the linear Rashba-Dresselhaus term to produce an unusual pattern of out-of-plane spin components in the spin texture.