Symmetry breaking induces room-temperature interface ferroelectricity in two-dimensional metastable mosaic-like heterostructures.

Metastable structures exhibiting unique properties hold significant potential for electronic applications. However, their inherent tendency to transform into thermodynamically more stable phases presents substantial challenges, as the stabilization of such metastable phases typically necessitates extreme conditions and complex synthesis strategy. Here, we demonstrate the synthesis of a metastable SmO2/Sm2O3 mosaic-like lateral heterostructure using molten eutectic salt. While both SmO2 and Sm2O3 are individually centrosymmetric, interfacial symmetry breaking at the junction simultaneously suppresses screw symmetry and inversion symmetry, resulting in a locally non-centrosymmetric configuration with broken spatial inversion. This structural asymmetry induces an intrinsic built-in dipole, a nonlinear optical response, and room-temperature interface ferroelectric polarization. Furthermore, vertically oriented interfaces provide confined pathways for directional ion transport, suppressing non-directional diffusion. Memristors based on the metastable heterostructure exhibit high performance, characterized by a maximum on/off ratio exceeding 109, switching speeds as fast as 47.3 ns, and retention times surpassing 104 s. The switching mechanism is consistent with field-driven oxygen vacancy migration along the vertical heterointerface, regulated by reversible oxygen adsorption and desorption at the electrode. This work offers a potential route for developing high-performance memristors leveraging metastable oxide heterointerfaces with coupled ferroelectric-like polarization and resistive switching functionalities.