Fig. 4: Theoretical calculations on ferroelectricity in GaSe.
From: Emergence of ferroelectricity in a nonferroelectric monolayer
a–c STEM images of distorted Q phase (a), non-distorted H phase (b), and distorted Q’ phase (c) of GaSe. The distorted Q’ phase is generated by intralayer sliding of the Q phase after the applied electric field polarization. The insets are enlarged images, respectively. d The geometric structure of the Q, H, and Q’ phases GaSe monolayer. The orange, dark green, and light green balls denote Ga atoms and Se atoms of the upper sublayer and bottom sublayer. The red and blue arrows represent the direction of polarization. e The differential charge density between the upper sublayer and bottom sublayer in real space (isosurface 0.0025 e/Bohr3, left panel) and corresponding planar averaged differential charge density (right panel) in the GaSe monolayer. The blue and pink colors represent electron accumulation and depletion regions, respectively. f The local potential of the Q phase along the z direction in monolayer. g The variation of OOP (blue dots) polarization is described by Se atom displacement, and the zero displacements are defined as the H phase. h The differential charge density between the topmost Q phase and the remaining layers in real space (isosurface 0.0001 e/Bohr3, left panel) and corresponding planar averaged differential charge density (right panel) in bilayer GaSe. The light blue and yellow colors represent electron accumulation and depletion regions, respectively. i The local potential of the Q phase along the z direction in the bilayer.
