Room-Temperature Ferroelectricity in 1 T′ - ReS2 Multilayers

van der Waals materials possess an innate layer degree of freedom and thus are excellent candidates for exploring emergent two-dimensional ferroelectricity induced by interlayer translation. However, despite being theoretically predicted, experimental realization of this type of ferroelectricity is scarce at the current stage. Here, we demonstrate robust sliding ferroelectricity in semiconducting 1T′-ReS2 multilayers via a combined study of theory and experiment. Roomerature vertical ferroelectricity is observed in two-dimensional 1T′-ReS2 with layer number N≥2. The electric polarization stems from the uncompensated charge transfer between layers and can be switched by interlayer sliding. For bilayer 1T′-ReS2, the ferroelectric transition temperature is estimated to be ∼405 K from the second harmonic generation measurements. Our results highlight the importance of interlayer engineering in the realization of atomic-scale ferroelectricity.