原子層二次元半導体の励起子状態と光学特性の計算

概要

令和 4 年度

京都大学化学研究所 スーパーコンピュータシステム 利用報告書
原子層二次元半導体の励起子状態と光学特性の計算

Simulation of exciton states and optical properties in atomically thin semiconducting materials
Optical Nano-science group, Institute of Advanced Energy, Kyoto University
Wang Haonan
研究成果概要
The supercomputer system has been used for the ab initio simulation on the linear and
nonlinear optical properties of thin layer SnS. Among the two-dimensional group IV
monochalcogenides, tin monosulfide (SnS) has drawn much attention due to its superior optical
and electronic properties. The monolayer SnS with the lack of inversion symmetry and in-plane
anisotropy shows potential in the application of piezoelectric nanogenerators. The inversion
symmetry and in-plane anisotropy has been evaluated by linear and nonlinear optical methods.
However, the novel optical properties arising from inversion symmetry and in-plane anisotropy
have not been fully understood in bilayer and thick layer SnS with various stacking structures.
Herein, we intend to investigate the linear and nonlinear optical properties of SnS by ab initio
simulation method.
Here, Quantum Espresso and Yambo code have been used in the supercomputer system for the
ab initio simulation studies [1,2]. The bilayer SnS with four different stacking structures
including AA stacking, AB stacking (α- and ’-type), and AC stacking are simulated. We have
calculated the optical absorption spectra of bilayer SnS with consideration of many-body effect
by solving Bethe-Salpeter equations. The absorption spectra clearly change according with the
in-plane electric-field direction, which suggests the strong anisotropic wavefunction distribution
of exciton states. The second harmony generation (SHG) susceptibility is also calculated under
various field directions. We have also simulated the polar-pattern of SHG intensity in AB
stacking bilayer SnS in the parallel and perpendicular detected configuration. The strong and
anisotropic SHG intensity also implies the anisotropic piezoelectricity. These results could
provide useful information towards the application of SnS in piezoelectric devices.
[1] P. Giannozzi et al., J. Phys.: Cond. Mat. 29, 465901 (2017).
[2] D. Sangalli et al., J. Phys.: Cond. Mat. 31, 325902 (2019). ...