Samuel Brem has developed theoretical models and computer simulations to explore the properties and dynamics of excitations in two-dimensional quantum materials.
Photo: Helén Rosenfeldt
Samuel Brem, Physics
Title of thesis: "Microscopic theory of exciton dynamics in two-dimensional materials"
When a material is illuminated with light, electrons jump from their ground state to an excited level and leave a “hole” behind. This hole is positively charged and attracts the negative electron. In atomically-thin films of transition metal dichalcogenides (TMDs), a new class of quantum materials, the forces between electrons and holes are so strong that they start to orbit each other and form extremely stable pairs, so-called excitons. The concept of excitons was already introduced by Yakov Frenkel in 1931 but just the recent development of atomically-thin TMDs has brought excitons into the focus of material research. These 2D materials have the potential to revolutionize the electronics industry by enabling new nanoscale device concepts. However, the key to technological applications of TMDs is a fundamental understanding of excitons.
In this work we have developed a theoretical model of excitons in TMDs. We provide microscopic insights into the motion of excitons and their interaction with light or crystal vibrations. In particular, we identify the impact of hidden so-called dark states. We also show how exciton properties change when two different TMDs are stacked. Here, we discuss how the resulting super periodic crystal structure, the moire pattern, can trap excitons into an array of light emitters. We applied our theoretical models to explain a large variety of experiments and gained microscopic insights into the dynamics of excitons in 2D quantum materials.
Main Supervisor: Ermin Malic
Examiner: Jari Kinaret
Faculty Opponent: Professor Wang Yao, University of Hong Kong
PJ, seminar room, NOTE! Entrance via Fysikgården 2 for external visitors
23 November, 2020, 09:00
23 November, 2020, 11:00