Fig. 1: Polarization flipping in a 2D vdW bilayer material via intralayer movement or interlayer sliding, and related symmetries.
From: Non-synchronous bulk photovoltaic effect in two-dimensional interlayer-sliding ferroelectrics
a A 2D system with positive out-of-plane polarization +P. b The polarization is reversed to –P by atom displacements in each monolayer, and the black arrow means the movement of the cations relative to the anions. c The polarization is reversed by interlayer sliding and the black arrows mean the interlayer sliding direction. d Three basis vectors and their transformations under e inversion symmetry f horizontal mirror symmetry. The black rectangles denote the bilayer unit cells in (a)-(c), and the gray rectangles denote the monolayer unit cells.
