Direct observation of geometric and sliding ferroelectricity in an amphidynamic crystal

Abstract

Sliding ferroelectricity is a recently observed polarity existing in two-dimensional materials. However, due to their weak polarization and poor electrical insulation in these materials, all available experimental evidence till now are indirect, with most based on transport properties in the nanoscale or piezoresponse force microscopy. We report the direct observation of sliding ferroelectricity, using a high-quality amphidynamic single crystal, (15-Crown-5)Cd${}_3$Cl${}_6$, which possesses a large band-gap and so allows direct measurement of P-E hysteresis. This coordination polymer is a van der Waals material, which is composed of inorganic stators and organic rotators as measured using XRD and NMR characterisation. From DFT calculations, we find that after the freezing of rotators an electric dipole is generated in each layer driven by the geometric mechanism, meanwhile a comparable ferroelectric polarization originates from the interlayer sliding. The net polarization of these two components can be directly measured and manipulated. Our finding provides insight into low-dimensional ferroelectrics, especially the controlling of synchronous dynamics of rotating molecules and sliding layers in solids.

21 pages, 5 figures

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• Switchable anomalous Hall effects in polar-stacked 2D antiferromagnet MnBi2Te4
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• Magnetic Antiskyrmions in Two-Dimensional van der Waals Magnets Engineered by Layer Stacking
• Large in-plane negative piezoelectricity and giant nonlinear optical susceptibility in elementary ferroelectric monolayers
• Phonon chirality manipulation mechanism in TMD interlayer-sliding ferroelectrics
• Ubiquitous van der Waals altermagnetism with sliding/moire ferroelectricity
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• Noncollinear ferroelectric and screw-type antiferroelectric phases in a metal-free hybrid molecular crystal
• Room-Temperature Noncolinear Ferroelectricity in van der Waals WO${}_2$Cl${}_2$ with a Wide Bandgap
• Sliding and superlubric moiré twisting ferroelectric transition in HfO2
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