An unexpected vortex field by twist
Twisted bilayer two-dimensional (2D) materials have emerged as a versatile platform for exploring quantum phenomena absent in their bulk counterparts, primarily due to reduced dimensionality and strong quantum confinement. While extensive research has focused on electronic structure modification and flat-band formation in twisted bilayers, the spatially varying electric field, particularly the polarized electric field at large twist angles, remains largely unexplored. This highlight examines the recent discovery of topological electric field structures in twisted bilayer molybdenum disulfide (MoS2) by Ly, Zhao, and Yang. Using four-dimensional scanning transmission electron microscopy (4D-STEM) and theoretical calculations, they uncovered topological vortex polarization domains corresponding to periodic Moiré patterns at varying twist angles. The study reveals twist-angle-dependent polar vortex textures, ranging from intricate vortex patterns to twelve-fold quasicrystal polar domains, with chiral features exhibiting clockwise and anti-clockwise swirling patterns in AB and BA regions, respectively. At a twist angle of 30°, an incommensurate quasicrystal structure with 12-fold rotational symmetry emerges, featuring rich polar vortex patterns that can be precisely manipulated via interlayer sliding at the picometer scale. First-principles calculations indicate that these in-plane polar vortex domains arise from twist-induced interfacial charge redistribution, with a minor contribution from in-plane ionic displacements. These findings elucidate the correlation between local atomic structures and 3D spatial electric field distributions, opening new avenues for tailoring polarization at the nanoscale.