The Rashba effect, characterized by spin splitting in band structures and helical spin textures, plays a pivotal role in various spintronics. However, the nonvolatile modulation of the Rashba splitting magnitude ${\alpha }_R$ in a single material, which potentially gives rise to novel spintronics, still remains unrealized. Here by using density-functional-theory calculations, we theoretically demonstrate the quadruple-well ferroelectrics (FEs) ${\left(\mathrm{Pt},\mathrm{Pd}\right)}_2\mathrm{S}{\mathrm{n}}_2\mathrm{T}{\mathrm{e}}_6$, featured by four stable FE states, $\pm \mathrm{high}$- and $\pm \mathrm{low}$-polarization states ($\pm \mathrm{HP}$ and $\pm \mathrm{LP}$ states), and enable the nonvolatile interconversion between strong and weak Rashba splitting mediated by the HP-LP transformation. Given that the band anticrossing, the typical feature of topologically nontrivial band structures, is associated with the strong Rashba splitting, such HP-LP transformation also enables the topological phase transition between a topological insulator and a conventional semiconductor. The intercoupling between ferroelectricity, Rashba splitting, and band topology provides a unique mechanism for modulating the ${\alpha }_R$ and topological characteristics in a nonvolatile way, paving ways for various novel spintronics and topological electronics.

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• Ferroelectricity
• Spin-orbit coupling
• Topological order
• 2-dimensional systems
• First-principles calculations