Effective nodal topological superconductivity driven by s -wave pairing and the ferromagnetic proximity effect in materials with persistent spin textures

Nodal topological superconductivity (NTSC) with flat Majorana boundary modes connecting gapless nodal points represents a nontrivial superconductivity (SC) phase capable of fault-tolerant topological quantum computing. In addition to unconventional SC with nodal pairing gap, two-dimensional (2D) NTSC has been effectively achieved from conventional $s$-wave SC by applying a magnetic field to symmetry-protected out-of-plane persistent spin texture (PST). Here we demonstrate that the effective NTSC can be alternatively achieved from in-plane PST under the ferromagnetic proximity effect, where the gapless nodal points within the SC gap remain robust at the entire energy range of the PST-enforced nodal line electronic states. This discovery positions (110)-oriented GaAs/AlGaAs and InAlAs/InGaAs quantum wells with extrinsic in-plane PST as ready-made NTSC platforms. Meanwhile, we propose that intrinsic in-plane PST is available in 2D stoichiometric materials with ${C}_2v$ or ${D}₂$ point group symmetry by balancing different antisymmetric spin-orbit coupling effects. Our first-principles calculations indicate the balance is readily struck in monolayer $X\mathrm{ThB}{\mathrm{r}}₆$ ($X=\mathrm{Ca}$, Sr, Ba) with ${C}_2v$ symmetry, while ${D}₂$ symmetry enforced in-plane PST is identified in $\mathrm{Au}{\mathrm{O}}₂\mathrm{Br}$ and $\mathrm{Cu}{\mathrm{O}}₂\mathrm{F}$ monolayers. This work not only expands the theoretical framework of effective NTSC, enabling its implementation in experimentally prepared quantum wells, but it also introduces a feasible route to achieve intrinsic in-plane PST in 2D stoichiometric compounds for device miniaturization.