Polymorphic Ferroelectricity in Artificially Stacked MoS₂ Interfaces

Original ferroelectricity has been observed in van der Waals (vdW) layered materials, where atomic layer lattice sliding can break the lattice inversion symmetry and induce ferroelectricity. While ferroelectricity in conventional bulk ferroelectric materials, driven by atomic (ionic) displacement for electric polarization, is stable at low temperatures, ferroelectricity in vdW materials has exhibited inconsistent temperature dependences, and its various origins reflecting clean vdW interfaces remain to be clarified. In this study, we demonstrate the unique temperature characteristics of polymorphic ferroelectricity in artificially stacked MoS2 interfaces, probed by transport experiments with edge contacts at various temperatures. In artificially stacked systems with MoS2 multilayers, two types of interface lattice stacking orders can be formed: rhombohedral (R) and hexagonal (H) stacking orders. In R-stacked MoS2, ferroelectricity occurs above a critical temperature T = 210 K, and charge trap behaviors are observed below the critical temperature. However, in H-stacked MoS2, charge trap behaviors dominate the transport above T = 210 K, while ferroelectricity is observed below the critical temperature. The nontrivial temperature dependence of polymorphic ferroelectricity in the R- and H-stacked vdW interfaces can be explained by the distinct roles of thermal energy in the atomic layer lattice sliding and moiré band splitting, paving the way toward advanced applications of polymorphic ferroelectric devices.