Interaction of 2D Excitonic Complexes with their Environment

Abstract

Two-dimensional materials are one of the most intensively studied systems in the modern solid state physics. Among the broad variety of currently known 2D materials, monolayer transition metal dichalcogenides (TMDC) are especially interesting. These materials exhibit strong light-matter interactions due to the presence of various types of excitons – bound states of charged carriers. Since every atom of a 2D material belongs to the surface, excitons in TMDCs are strongly influenced by their environment. Therefore, in order to understand the physical properties of 2D excitons it is critical to understand how these excitons interact with their environment. In this work, we study one of the most prominent interaction mechanisms – electromagnetic coupling between 2D excitons and their environment. We start with investigating basic properties of excitons in pristine suspended TMDCs decoupled from the environment. We reveal the exciton types, determine their binding energies and uncover dissociation mechanisms. Then, we probe relatively simple interaction mechanism – resonant energy transfer between 2D excitons and their environment. We demonstrate that rate of such interactions can be controlled by changing the Fermi level of the 2D material. Finally, we investigate a more complex phenomenon – dynamic, or frequency-dependent, screening of excitons by environment. We develop a simple theoretical model to understand dynamic screening and then experimentally test our predictions.