Universal superlattice potential for 2D materials from twisted interface inside h-BN substrate

Abstract

Lateral superlattices in 2D materials provide a powerful platform for exploring intriguing quantum phenomena, which can be realized through the proximity coupling in forming moiré pattern with another layer. This approach, however, is invasive, material-specific, and requires small lattice mismatch and suitable band alignment, largely limited to graphene and transition metal dichalcogenides (TMDs). Hexagonal boron nitride (h-BN) of antiparallel (AA′) stacking has been an indispensable building block, as dielectric substrates and capping layers for realizing high-quality van der Waals devices. There is also emerging interest on parallelly aligned h-BN of Bernal (AB) stacking, where the broken inversion and mirror symmetries lead to out-of-plane electrical polarization. Here we show the that laterally patterned electrical polarization at a nearly parallel interface within the h-BN substrate can be exploited to create noninvasively a universal superlattice potential in general 2D materials. The feasibility is demonstrated by first principle calculations for monolayer MoSe2, black phosphorus, and antiferromagnetic MnPSe3 on such h-BN. The potential strength can reach 200 meV, customizable in this range through choice of distance of target material from the interface in h-BN. We also find sizable out-of-plane electric field at the h-BN surface, which can realize superlattice potential for interlayer excitons in TMD bilayers as well as dipolar molecules. The idea is further generalized to AB-stacked h-BN subject to torsion with adjacent layers all twisted with an angle, which allows the potential and field strength to be scaled up with film thickness, saturating to a quasi-periodic one with chiral structure.

Analytical Theory of Near-Field Electrostatic Effects in Two-Dimensional Materials and van der Waals Heterojunctions

“…a is 2.51 Å, 3.13 Å, and 3.21 Å for h-BN, h-AlN, and h-GaN, respectively. We note that the out-of-plane e −4πd √ 3a decay for h-BN has been previously reported in the literature [35].…”

“…2(b,c). The out-of-plane decay constant is also much weaker (β = 1.19 Å−1 ), in accordance with the larger inplane lattice parameters [12,[35][36][37]. This is in agreement with previous works [35][36][37] and suggests that the electrostatic potential at such distances can be well approximated by a functional form V (x, y, d) f (x, y)e −βd , with f (x, y) depending on the atomic positions and β depending on the lattice parameter and symmetry, which we now derive.…”

“…With the discovery of exotic phenomena in moiré systems [22][23][24][25], accurate continuum models of the interlayer interactions and structural relaxations that connect macroscopic geometric descriptors to microscopic effective low-energy Hamiltonians have been proposed [26][27][28][29], leading to plethora of predictions of exotic electronic states [30][31][32][33][34]. However, while the nearfield electrostatic potential has been extracted from density functional theory (DFT) [35], to the best of our knowledge, no simple closed form of the near-field interactions experienced in 2D materials assemblies or moiré structures has been proposed.…”

Identifying the Transition Order in an Artificial Ferroelectric van der Waals Heterostructure

“…In recent years, novel atomically thin ferroelectric semiconducting materials have been synthesized and are generically known as group-IV monochalcogenide monolayers, which exhibit stable ferroelectrics at the monolayer level. − However, these materials usually suffer from lack of chemical stability, making their potential applications in memory challenges. Unlike conventional epitaxial growth, van der Waals (vdW) integration offers an alternative strategy to tailor and engineer crystal symmetry by simply stacking and rotating different building blocks, − as exemplified by two-dimensional (2D) twist electronics. − Recently, artificial ferroelectrics created by tearing-and-stacking bipartite honeycomb 2D materials have been theoretically predicted and experimentally realized in the parallel hexagonal boron nitride (hBN) bilayer system − and very recently in semiconducting transition metal dichalcogenides (s-TMDs). , For these materials, the ferroelectric phase transitions have not yet been carefully studied, and the phase transition order has not been identified experimentally.…”

Spatially Resolved Polarization Manipulation of Ferroelectricity in Twisted hBN

“…Another exciting property, ferroelectricity, was recently realized in twistronics. Ferroelectric domains can be developed by placing two layers of hexagonal boron nitride (hBN) together with a small rotation [ 5–8 ] and detected using piezo force microscopy (PFM), [ 9–11 ] electrostatic force microscopy, [ 12,13 ] or nano‐infrared microscopy. [ 11 ] Besides hBN, other 2D transitional metal dichalcogenides with a small twist are also being actively explored owing to their ferroelectricity.…”