March 1, 2023
Screening in Low-Dimensional Systems: Understanding its Influence on Quasiparticle and Optical Properties from First Principles
The optoelectronic properties of two-dimensional (2D) semiconductors are highly sensitive to the surrounding dielectric environment, a direct result of the intrinsic weak and highly non-local dielectric screening in low-dimensional systems. In this seminar, I will discuss two types of screening: free charged carrier screening and non-local adsorbate/substrate screening, which are particularly relevant in experimentally grown 2D transition metal dichalcogenides (TMDs) and render the measurement and interpretation of their electronic and optical spectra non-trivial. First-principles calculations can guide understanding of screening effects on optoelectronic properties of low-dimensional systems. I will first introduce the state-of-the-art ab initio GW plus Bethe Salpeter equation (GW+BSE) approach used to accurately predict one and two particle excitations, respectively. I will then show how the electronic and optical properties of a monolayer MoTe2 are modified due to the presence of free carriers, for experimentally-achievable carrier density. Eventually, I will discuss the energy level alignment and optical response of an organic-inorganic bilayer system, formed by a monolayer TMD decorated with PTCDA molecular adsorbates.
Dr. Aurelie Champagne is a postdoctoral researcher in the group of Jeffrey B. Neaton at the Lawrence Berkeley National Laboratory. In 2020, she received her Ph.D. in science engineering and technology from the Institute of Condensed Matter and Nanosciences at UCLouvain (Belgium) where she studied the physical properties of a novel family of two-dimensional materials, MXenes, combining experiments and ab initio calculations. Aurelie Champagne’s current research interest includes the development and application of theoretical models to predict the electronic, optical, and transport properties in low-dimensional materials, with foreseen applications in optoelectronic and energy-related devices.