Across‐Layer Sliding Ferroelectricity in 2D Heterolayers

Abstract

Although the monolayers of most 2D materials are non-ferroelectric with highly symmetric lattices, symmetry breaking may take place in their bilayers upon some stacking configuration, 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 (Nature 2020, 588, 71) in graphene bilayer intercalated between h-BN remains mysterious. Here, a type of across-layer sliding ferroelectricity that arises from the asymmetry of next-neighbor interlayer couplings is proposed. The first-principles evidence is shown that the vertical polarizations in intercalated centro-symmetric 2D materials like graphene bilayer can be switched via multilayer sliding, which is likely to be the origin of the observed ferroelectric hysteresis. Moreover, such ferroelectricity may exist in a series of other heterolayers with quasidegenerate 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.

Moiré Synergy: An Emerging Playground by Coupled Moirés

“…For decades, ferroelectricity and ferromagnetism had been considered as collective phenomena in bulky materials, until the recent boom of vdW materials and their heterostructures, especially the unconventional ferroelectricity − ,,, and ferromagnetism in moiré superlattices of nonferroic layers. It is exciting if we could integrate both ferroelectric and ferromagnetic moirés into multiferroic devices through the coupled-moiré schemes.…”

“…The prominent interlayer interactions , make the constituent atomic orbitals interfere constructively to manifest a superlattice of much larger wavelengths than the component lattice parameters, so that the energy band edges significantly flatten in the reciprocal space, nourishing a plethora of exotic quantum phenomena, such as superconductivity, correlated insulators, orbital magnetism, and unusual ferroelectricity . Notably, following the theoretic establishment of 2D ferroelectricity induced by interlayer translation, the experimental demonstrations of sliding ferroelectricity in various 2D stacks have boomed in the past few years. − …”

Stacking Order Engineering of Two-Dimensional Materials and Device Applications

“…Figure 7a shows the observed ferroelectric switching in a device with the top and bottom graphene rotated by ∼30°, 116 and Figure 7b,c shows the across-layer sliding model (b) and proposed switching pathway (c). 118…”

Phonon Chirality Manipulation Mechanism in Transition-Metal Dichalcogenide Interlayer-Sliding Ferroelectrics

“…Surprisingly, a unique ferroelectric mechanism was proposed in 2017sliding ferroelectricity . The 2D interlayer-sliding ferroelectric material is composed of a monolayer material without ferroelectric polarization, and ferroelectric state switching is caused by sliding between the upper and lower layers. − The concept has received intense attention from researchers and was recently demonstrated experimentally by Yasuda et al and Stern et al…”