Sliding ferroelectricity in van der Waals 2D materials: associated physics and future opportunities



As the 100th anniversary of the discovery of ferroelectricity approaches, so-called slippery ferroelectricity has been proposed and recently confirmed in a series of experiments that have generated remarkable interest. Such ferroelectricity widely exists and only exists in two-dimensional (2D) van der Waals stacked layers, where the vertical electrical polarization is switched by inter-layer slip in the plane. Conversely, inter-layer slip and the wall of the “ripplocation” domain can be driven by an external vertical electric field. The unique combination of intralayer stiffness and interlayer slippage of van der Waals 2D layers greatly facilitates such switching while maintaining environmental and mechanical robustness under ambient conditions. From this perspective, we discuss the progress and future opportunities of this behavior. The origin of such ferroelectricity as well as a general rule for judging its existence are summarized, where the vertical stacking sequence is crucial for its formation. This discovery expands 2D ferroelectrics from very few candidate materials to most of the known 2D materials. Their low switching barriers allow high speed data writing with low power cost. Associated physics such as Moiré ferroelectricity, ferroelectric nonlinear anomalous Hall effect and multiferroic coupling are discussed. For 2D valleytronics, the nontrivial band topology and superconductivity, their possible couplings with sliding ferroelectricity via certain stacks or Moiré ferroelectricity are also of interest. We provide critical reviews on current challenges in this emerging field.


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