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.

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• Electronic structure
• Spin-orbit coupling
• 2-dimensional systems
• Density functional theory
• First-principles calculations
• Tight-binding model