Fig. 1: Crystal structure and band structure of layered SiP2.
From: Unconventional excitonic states with phonon sidebands in layered silicon diphosphide
a, Schematic layered structure of SiP2 (Pnma, group number 62). The x,y,z coordinate system is defined according to the crystal structure, as shown in the bottom-left corner. The blue shading highlights the PB–PB chains formed by the PB atoms along the y direction of the crystal lattice, which play a critical role in generating quasi-1D electronic and excitonic states. b–d, Top view (b) and cross-sectional (c,d) STEM–ADF images of SiP2 viewed along the y axis (c) and x axis (d). Green and cyan dashed rectangles represent the periodic lattice with ABAB stacking order of SiP2 layers. Scale bars, 1 nm. e, Electronic band structure of bulk SiP2 calculated from the GW method. The inset shows the first BZ of bulk SiP2. SiP2 is a semiconductor with an indirect band gap of 2.14 eV. The valence band maximum is at the Γ point, and the conduction band minimum is located along the Γ–Y direction. The conduction band minimum state does not contribute to the formation of the A exciton due to the large direct interband transition energies at this location. f, Charge density distribution of the conduction band edge (left) and valence band edge (right) in real space. The isosurface of the plot is 0.02 e Å−3.
