Doping charges into noncoplanar spiral textures provide opportunities for the development of multifunctional memory devices. Here, we demonstrate that two-unit-cell-thick twisted bilayer ${\mathrm{SrTiO}}_3$ undergoes ferroelectric-to-magnetic ferroelectric and semiconducting-to-half-metallic transitions, thereby reviving and stabilizing the topological order inherent in twisted perovskite. The underlying mechanism for realizing the transitions is attributed to a quasi-two-dimensional electron gas localized around Ti atoms. Ti displacements occur along the out-of-plane polar direction, while the in-plane square-planar ${\mathrm{TiO}}_4$ cage retains fourfold rotation $\left(C_4\right)$ symmetry with the degenerate $d_{xz}$ and $d_{yz}$ orbitals. Doubly degenerate orbitals accommodate ultrahigh electron-doping concentrations, leading to the coexistence of half-metallicity and layer-antiferromagnetic order. The ground-state magnetic phase diagram is established, and the transition temperature is evaluated as a function of doping concentration. Furthermore, significant ionic displacements break inversion symmetry and permit a shear piezoelectric response. The twisted structure belongs to the point group 422, which restricts the piezoelectric tensor to pure face-shear components. These findings provide an intrinsic mechanism for achieving skyrmion patterns, half-metallicity, magnetism, and piezoelectric responses in ultrathin twisted bilayer perovskite.

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• Charge
• Density of states
• Doping effects
• Electronic structure
• Magnetism
• Piezoelectrics
• Skyrmions
• Half-metals
• Multiferroics
• Perovskites
• Twisted heterostructures
• DFT+U
• First-principles calculations