Emergence of cubic ordered full-plane persistent spin textures in lead-free materials

The materials preserving a uniform spin configuration in the momentum space, known as persistent spin texture (PST), provide long carrier spin lifetimes through persistent spin-helix mechanism. However, most of the PSTs studied until now are attributed to the linear in $\mathbit{k}$ splitting and cease to exist locally around certain high-symmetry points of the first Brillouin zone (BZ). The PSTs with purely cubic spin splittings (PCS) have drawn attention owing to unique benefits in spin transport. Here, using relativistic first-principles calculations supplemented with $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ analysis, we report the emergence of PCS belonging to ${D}_3h$ point group, which is enforced by in-plane mirror and threefold rotation operations. In addition, the in-plane mirror symmetry operation sustains the PST in a larger region, i.e., full planes of BZ alongside giant spin splitting. The observed PSTs provide a route to nondephasing spin transport with larger spin Hall conductivity, thereby offering a promising platform for future spintronics devices.