Polymorphic Ferroelectricity in Artificially Stacked\nMoS<sub>2</sub> Interfaces

Original ferroelectricity has been\nobserved in van der Waals (vdW)\nlayered materials, where atomic layer lattice sliding can break the\nlattice inversion symmetry and induce ferroelectricity. While ferroelectricity\nin conventional bulk ferroelectric materials, driven by atomic (ionic)\ndisplacement for electric polarization, is stable at low temperatures,\nferroelectricity in vdW materials has exhibited inconsistent temperature\ndependences, and its various origins reflecting clean vdW interfaces\nremain to be clarified. In this study, we demonstrate the unique temperature\ncharacteristics of polymorphic ferroelectricity in artificially stacked\nMoS<sub>2</sub> interfaces, probed by transport experiments with edge\ncontacts at various temperatures. In artificially stacked systems\nwith MoS<sub>2</sub> multilayers, two types of interface lattice stacking\norders can be formed: rhombohedral (R) and hexagonal (H) stacking\norders. In R-stacked MoS<sub>2</sub>, ferroelectricity occurs above\na critical temperature <i>T</i> = 210 K, and charge trap\nbehaviors are observed below the critical temperature. However, in\nH-stacked MoS<sub>2</sub>, charge trap behaviors dominate the transport\nabove <i>T</i> = 210 K, while ferroelectricity is observed\nbelow the critical temperature. The nontrivial temperature dependence\nof polymorphic ferroelectricity in the R- and H-stacked vdW interfaces\ncan be explained by the distinct roles of thermal energy in the atomic\nlayer lattice sliding and moiré band splitting, paving the\nway toward advanced applications of polymorphic ferroelectric devices.