# Multiple Linear Dichroism Inversions in SnO Monolayers for Polarization-Sensitive UV Photodetection: An Ab Initio Investigation

## TL;DR

This paper investigates how the unique structure of SnO monolayers leads to unusual light absorption properties, making them promising for polarization-sensitive UV photodetection.

## Contribution

The paper reveals multiple linear dichroism inversions in SnO monolayers due to their reduced symmetry and anisotropic electronic structure.

## Key findings

- SnO monolayers exhibit in-plane anisotropy affecting electronic states and optical absorption.
- Multiple linear dichroism inversions are observed between 200 and 400 nm wavelengths.
- Optical dichroism can be used to study the ferroelastic-to-paraelastic transition in SnO monolayers.

## Abstract

Tin monoxide (SnO)
undergoes a phase transition from litharge-like
tetragonal (space group P4/nmm)
to orthorhombic geometry (layer group pmmn) in passing
from multilayer to monolayer crystals. By means of ab initio ground
and excited-state methods, we explore the impact of the reduced pmmn spatial symmetry on the electronic and optical properties
of SnO monolayers. As a consequence of the in-plane anisotropy, the
electronic states of the band edges show asymmetric projections onto
the px and py atomic orbitals along orthogonal directions in the Brillouin zone.
This results in optical absorption and exciton properties that are
highly sensitive to the direction of in-plane polarized light. In
contrast to typical linear dichroic materials, which generally favor
the absorption of one polarization over the orthogonal one across
a wide frequency range, we show that SnO monolayers display linear
dichroism inversion. Here, the energy ordering of the exciton states
causes the two orthogonal polarizations to be absorbed with different
intensities depending on the light frequency. We observe multiple
inversions of the linear dichroism across wavelengths from 200 to
400 nm. These properties make SnO monolayers promising candidates
for further exploration of low-symmetry, two-dimensional materials
for advanced applications in polarization-sensitive nanoscale devices.
In addition, we propose utilizing optical dichroism measurements as
a means to probe the recently predicted ferroelastic-to-paraelastic
transition of SnO monolayers.