Tracking Polarization Structure in PtTe₂ at Three-Dimensional Atomic Resolution

Spontaneous polarization due to symmetry breaking in the transition metal ditellurides (MTe₂) family exhibits intriguing sliding ferroelectricity. Although theoretical predictions of MTe₂ ferroelectric metals with noncentrosymmetric stacking have been reported, the realization of such polarization structure remains a challenge. Here, we demonstrate the synthesis of PtTe₂ with non-centrosymmetric stacking layers, in contrast to bulk AA stacking, achieved within a scanning transmission electron microscope (STEM) by irradiating amorphous Pt_xTe_y thin films with an electron beam probe. Cross-sectional STEM imaging combined with first-principles calculations reveals that the diverse stacking configurations due to an intralayer π-stacking system break centrosymmetry in PtTe₂, giving rise to the out-of-plane polarization. Three-dimensional atomic positions identified by the atomic electron tomography method further demonstrate the local distortions associated with the non-centrosymmetric stacking layers in PtTe₂. The understanding of the atomic origin of polarization in PtTe₂ is of significant importance for developing devices that integrate ferroelectricity with metallicity.