P4: Many-body Optics of TMDs and Black Phosphorus

Supervision:Christopher Gies, Tim Wehling

Motivation and state of the art: In the wake of graphene, a class of new materials has emerged that only consist out of a single or few layers of atoms, but possess a direct band gap. Despite being atomically thin, they strongly interact with light, making them promising candidates for active materials in future generations of optoelectronic devices. Amongst these new semiconducting materials are transtition-metal dichalcogenides (TMDs) with band gaps in the visible range, and black phosphorus (BP) with a band gap in the infrared. Being atomically thin, TMDs and BP react sensitively to their environment, e.g. in the form of a substrate or heterostructure, and strain, which can be used to tailor and control their macroscopic properties. Emission and absorption of light is strongly determined by the Coulomb interaction, which correlates charge carriers (electrons and holes) into excitons and other species of semiconductor excitations.

Own work:We have developed an interdisciplinary approach that uses semiconductor many-body methods on the basis of material-realistic input from ab-initio G0W0 band-structure calculations and Coulomb matrix elements. We apply and advance these methods to describe optical properties taking into account excited carriers in the band structure. Graduate work in this project will strongly benefit from the challenge of bringing together expertise in different theoretical methods.

Aims and work plan: In the last year, investigations of many-body effects due to excited carriers were in the focus of TMD research. In P4 we aim at developing an understanding of the optical properties of these new materials under the influence of excited carriers and under device-relevant excitation conditions. We will investigate exciton and trion formation, dephasing of optical transitions (with P5), model non-equilibrium pump-probe experiments (with P5), study substrate effects (with P2), and develop new methods (with P1 and P9) to approach the complex topic of heterostructures of different atomically thin functional materials, with the goal to understand fundamental optical properties and to reveal application potential for future photofunctional devices.