LAUSR

First-principles simulations are conducted to predict that ferroelectric nitride perovskite $\mathrm{LaW}{\mathrm{N}}_{3}$ not only exhibits large spin splittings (2.7 eV \AA{}) but also possesses unique spin textures for some of its conduction levels. Such spin splittings around the $\mathrm{\ensuremath{\Gamma}}$ and $L$ points cannot be interpreted as a typical mixture of Rashba or Dresselhaus configurations but rather require the development of four-band $\mathbit{k}\ifmmode\bullet\else\textbullet\fi{}\mathbit{p}$ models with high-order terms. We further identify that, for some bands, spin splittings can be greatly contributed by the pure orbital degree of freedom (PODF), a unique character of our four-band Hamiltonian compared to the traditional two-band version. The concept of PODF-enhanced spin splittings paves a way for designing materials with large spin splittings. Moreover, the energy levels possessing such large splittings and complex spin textures can be brought close to the conduction-band minimum by applying epitaxial strain.