Undulation-induced moir\'e superlattices with 1D polarization domains and 1D flat bands in 2D bilayer semiconductors

TL;DR

This paper demonstrates how undulations in 2D bilayer semiconductors induce 1D polarization domains and flat bands, revealing a new way to engineer electronic properties through bending and shear patterns.

Contribution

It introduces the concept of 'curvytronics' by showing how undulation-induced shear and polarization create 1D moiré patterns and flat bands in 2D bilayer materials.

Findings

Undulation induces 1D polarization domains and flat bands.

Shear patterns create localized electronic states and 1D quantum-well-like bands.

Curvytronics offers a new approach to design electronic phases in 2D materials.

Abstract

Two-dimensional (2D) materials have a high F\"oppl-von K\'arm\'an number and can be easily bent, much like a paper, making undulations a novel way to design distinct electronic phases. Through first-principles calculations, we reveal the formation of 1D polarization domains and 1D flat electronic bands by 1D bending modulation to a 2D bilayer semiconductor. Using 1D sinusoidal undulation of a hexagonal boron nitride (hBN) bilayer as an example, we demonstrate how undulation induces nonuniform shear patterns, creating regions with unique local stacking and vertical polarization akin to sliding-induced ferroelectrics observed in twisted moir\'e systems. This sliding-induced polarization is also observed in double-wall BN nanotubes due to curvature differences between inner and outer tubes. Furthermore, undulation generates a shear-induced 1D moir\'e pattern that perturbs electronic states, confining them into 1D quantum-well-like bands with kinetic energy quenched in modulation direction while dispersive in other directions (1D flat bands). This electronic confinement is attributed to modulated shear deformation potential resulting from tangential polarization due to the moir\'e pattern. Thus, bending modulation and interlayer shear offer an alternative avenue, termed "curvytronics", to induce exotic phenomena in 2D bilayer materials.