Extremely flat band in antiferroelectric bilayer α-In₂Se₃ with large twist-angle

Abstract

The moiré-pattern with slightly interlayer-twisted bilayer two-dimensional (2D) materials has recently been receiving substantial attention. One of the major characters for these intriguing structures is the appearance of low-energy ultra-flat bands and thus a package of new physics associated with strong electron correlation emerges. However, such new physics may become vague unless the twist-angle θ is sufficiently small such as θ ∼ 1°, making practical applications and control-flexibility hard to handle. In this work, we explore the possible flat-band moiré physics in recently concerned 2D bilayer α-In2Se3 which is antiferroelectric with sublayer out-of-plane (OP) polarizations, addressing the potential role of polarization-bound charges in modulation of electron–electron correlation and interlayer hybridization, based on the extensive first-principles calculations. On one hand, it is found that the low energy band becomes extremely flat in the bilayer α-In2Se3 moiré-pattern with relatively large twist-angle, e.g. θ = 13.17°, which is more easily accessible experimentally. On the other hand, the impact of the sublayer OP polarizations on the band structure is asymmetric, and the flattening effect is much more remarkable for the end-to-end polarization alignment but weaker for the head-to-head alignment. This work thus opens a broad roadmap for technological access to artificial fabrication of novel moiré-patterned 2D materials by means of low-dimensional ferroelectricity.

Small twist, big miracle—recent progress in the fabrication of twisted 2D materials

“…θ = 13.17°, due to the appearance of moiré-patter. 157 Afterwards, a similar situation was also observed in the twisted bilayer InSe, 158 in which the bandwidth can be suppressed to be less than 10 meV at θ = 9.43°. Recently, Chen et al proved that the two Fe 3 GeTe 2 layers can implement an antiferromagnetic–ferromagnetic phase transition by constructing an interlayer rotation, 159 providing a feasible method to tune the interlayer magnetic ordering of 2D compounds.…”

Transport through quantum anomalous Hall bilayers with lattice mismatch

“…For example, a graphene bilayer, even regularly stacked as a periodic lattice, has possessed electronic structures and transport properties significantly different from those of a monolayer one [14]. By twisting bilayers into generic non-commensurate or quasi-periodic lattices, more nontrivial physics emerge, including strong correlation, superconductivity and nontrivial topology [15][16][17][18][19].…”

Theory of polar domains in moiré heterostructures

“…It has also been suggested that MPDs are antiferroelectric [56,57]. Although in 3R-stacked homo-bilayers the domains have opposite orientation and the polarization averages to zero, the classical definition of antiferroelectricity refers to anti-aligned adjacent dipoles, not adjacent domains, analogous to an antiferromagnet.…”