Optical properties of atomically thin transition metal dichalcogenides: Observations and puzzles

TL;DR

This paper reviews recent experimental findings on the optical properties of atomically thin transition metal dichalcogenides, highlighting current understanding, open questions, and phenomena related to valley physics and single photon emitters.

Contribution

It provides a comprehensive overview of experimental observations and discusses the limitations of existing models in explaining the optical behavior of these materials.

Findings

Observation of valley-related phenomena in magnetic fields

Detection of single photon emitters in layered materials

Identification of open questions in optical properties understanding

Abstract

Recent results on the optical properties of mono- and few-layers of semiconducting transition metal dichalcogenides are reviewed. Experimental observations are presented and discussed in the frame of existing models, highlighting the limits of our understanding in this emerging field of research. We first introduce the representative band structure of these systems and their interband optical transitions. The effect of an external magnetic field is then considered to discuss Zeeman spectroscopy and optical pumping experiments, both revealing phenomena related to the valley degree of freedom. Finally, we discuss the observation of single photon emitters in different types of layered materials, including wide band gap hexagonal boron nitride. While going through these topics, we try to focus on open questions and on experimental observations, which do not yet have a clear explanation.