Anisotropic Behavior of Excitons in Single Crystal {\alpha}-SnS

TL;DR

This study analyzes the anisotropic dielectric properties of single crystal { extalpha}-SnS, revealing prominent excitonic features along specific crystallographic directions due to orbital anisotropy, using first-principles calculations.

Contribution

It provides a detailed first-principles analysis of anisotropic excitonic behavior in { extalpha}-SnS, linking dielectric anisotropy to orbital characteristics.

Findings

Pronounced excitonic feature along the armchair axis at low temperatures.

Anisotropic dielectric properties are due to p orbital anisotropy.

The py orbital at the saddle point causes the dominant excitonic feature.

Abstract

We investigate analytically the anisotropic dielectric properties of single crystal {\alpha}-SnS near the fundamental absorption edge by considering atomic orbitals. Most striking is the excitonic feature in the armchair- (b-) axis direction, which is particularly prominent at low temperatures. To determine the origin of this anisotropy, we perform first-principles calculations using the GW0 Bethe-Salpeter equation (BSE) including the electron-hole interaction. The results show that the anisotropic dielectric characteristics are a direct result of the natural anisotropy of p orbitals. In particular, this dominant excitonic feature originates from the py orbital at the saddle point in the {\Gamma}-Y region.