Room-Temperature Noncollinear Ferroelectricity in van der Waals WO_{2}Cl_{2} with a Wide Bandgap.

Low-dimensional ferroelectrics are attractive for their promising prospects in nanoelectronics. Compared with widely used ferroelectric perovskites, most low-dimensional ferroelectrics exhibit several inborn weaknesses such as small bandgaps (mostly <2  eV, i.e., semiconductorslike) or faint polarizations (e.g., <1  μC/cm^{2} for sliding ferroelectrics even if their bandgaps can be large). Here we experimentally demonstrate the room-temperature ferroelectricity of van der Waals WO_{2}Cl_{2}. The well-tested d^{0} rule inherited from ferroelectric perovskites leads to a large dipole (∼3  eÅ) from the off-center displacement of W^{6+} ion and a wide bandgap of 2.80 eV. Its ferroelectricity is proved by multiple characterizations including second harmonic generation, piezoresponse force microscopy, and ferroelectric hysteresis loops. More interestingly, the exotic noncollinear dipole order is directly observed at the atomic level by integrated differential phase contrast scanning transmission electron microscopy. Our Letter paves an alternative route for low-dimensional ferroelectrics to pursue excellent ferroelectric performance and distinct physics of polarity.