Across-Layer Sliding Ferroelectricity in Graphene-Based Heterolayers: Asymmetry of Next Neighbor Interlayer Couplings

Although most two-dimensional (2D) materials are non-ferroelectric with highly symmetric lattices, symmetry breaking may take place in their bilayers upon certain stacking order, giving rise to so-called sliding ferroelectricity where the vertical polarizations can be electrically reversed via interlayer translation. However, it is not supposed to appear in systems like graphene bilayer with centro-symmetry at any stacking configuration, and the origin of the recently reported ferroelectricity in graphene bilayer intercalated between h-BN (Nature 2020, 588, 71) is still unclear. Here we propose a model of across-layer sliding ferroelectricity that arises from the asymmetry of next neighbor interlayer couplings. The vertical polarizations in intercalated centro-symmetric 2D materials like graphene bilayer can be switched via multilayer sliding, and the observed ferroelectric hysteresis can be clarified. Moreover, such ferroelectricity can exist in a series of other heterolayers with quasi-degenerate polar states, like graphene bilayer or trilayer on BN substrate, or even with a molecule layer on surface where each molecule can store 1 bit data independently, resolving the bottleneck issue of sliding ferroelectricity for high-density data storage.