Title: Tunable Exciton-polaritons in Band Gap Engineered Hexagonal Boron Nitride
When: Friday, April 26, 2024, 12:30
Place: Department of Theoretical Condensed Matter Physics, Faculty of Sciences, Module 5, Seminar Room (5th Floor)
Speaker: Pedro Antonio Correia Ninhos, Center for Polariton-driven Light-Matter Interactions (POLIMA), University of Southern Denmark.
Monolayer hexagonal boron nitride (hBN), is one of the most promising 2D materials for optoelectronics, since as a large band gap semiconductor, it displays an intense absorption in the ultraviolet range. Due to the reduced thickness of 2D materials, they show a reduced dielectric screening, which makes it possible for formation of excitons with bigger excitonic binding energies compared to 3D semiconductors. Studies on the optical properties of hBN can be found in the literature, but there is the need for ways of controlling its excitonic properties. In the first part of the presentation, we suggest a form of tuning the excitonic binding energies by applying a one-dimensional periodic potential on top of hBN. In this way, we form a superlattice structure that has distinct electronic properties from the original lattice. It leads to the renormalization of the gap and of the electron and hole effective masses. We have seen that increasing the period of the potential increases the anisotropy of the dispersion, which results in the red-shift of the excitonic levels. We computed as well the optical conductivity, and have observed that the intensity of the peaks in the conductivity increases as the frequency of the peaks red-shift. We determine the dispersion relation of the exciton-polaritons that arise from the coupling of the exciton with light. In the second part of the presentation, we derive the Bethe-Salpeter equation, and from it the Wannier equation, and discuss the validity of the methods presented.
