Unraveling intrinsic flexoelectricity in twisted double bilayer graphene

Abstract

Moiré superlattices of two-dimensional (2D) materials with a small twist angle are thought to exhibit appreciable flexoelectric effect, though unambiguous confirmation of their flexoelectricity is challenging due to artifacts associated with commonly used piezoresponse force microscopy (PFM). For example, unexpectedly small phase contrast ($\sim$$8^{\circ }$) between opposite flexoelectric polarizations was reported in twisted bilayer graphene (tBG), though theoretically predicted value is $180^{\circ }$. Here we developed a methodology to extract intrinsic moiré flexoelectricity using twisted double bilayer graphene (tDBG) as a model system, probed by lateral PFM. For small twist angle samples, we found that a vectorial decomposition is essential to recover the small intrinsic flexoelectric response at domain walls from a large background signal. The obtained three-fold symmetry of commensurate domains with significant flexoelectric response at domain walls is fully consistent with our theoretical calculations. Incommensurate domains in tDBG with relatively large twist angles can also be observed by this technique. Our work provides a general strategy for unraveling intrinsic flexoelectricity in van der Waals moiré superlattices while providing insights into engineered symmetry breaking in centrosymmetric materials.

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Cited by in corpus (9)

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• Symmetry breaking and anomalous conductivity in a double moiré superlattice
• Energetic stability and spatial inhomogeneity in the local electronic structure of relaxed twisted trilayer graphene
• Layer-dependent electromechanical response in twisted graphene moiré superlattices
• Moiré Synergy: An Emerging Game Changer by Moiré of Moiré
• Quantifying the local mechanical properties of twisted double bilayer graphene
• Quantum geometric moment encodes stacking order of moiré matter
• Hexagonal network of photocurrent enhancement in few-layer graphene/InGaN quantum dot junctions
• Second-Order Synaptic Memory using Inherent Plasticity of Moiré Superlattices