The continuing trend to miniaturization of devices in modern technology faces fundamental physical limits of applied materials. The search for novel structures with new functionalities has brought atomically thin two-dimensional (2D) materials into the focus of current research. The most prominent respresentatives of this class of materials are graphene and transition metal dichalcogenides (TMDs). They show a wide range of exceptional optical and electronic properties suggesting technological application in next-generation of opto-electronic devices including lasers, photodetectors, and solar cells.
The rapidly growing research on these materials has revealed many fascinating features, however, most of the underlying many-particle phenomena have not been entirely understood yet. The main goals of the proposed project are (i) to provide fundamental insights into the coupled dynamics of excitons, electrons, phonons, and photons in graphene, TMD materials and related heterostructures and (ii) to exploit the gained knowledge to concretely model novel technological concepts based on these materials (such as photodetectors, lasers, molecule and strain sensors).
After an optical excitation, electrons are lifted from the valence up into the conduction band. These non-equilibrium electrons interact among each other as well as with the lattice transferring parts of their excess energy into lattice vibrations (phonons). On their way to an equilibrium distribution, they can accumulate close to the band minimum, however the probability for radiative recombination is very high resulting in light emission (photons). In TMD materials, the Coulomb interaction is so strong, that excitons as new quasi-particles are formed. They are electron-hole pairs with binding energies in the range of up to 1 eV. As a result, they are stable at room temperature and therefore excitonic effects dominate the optical response and the non-equilibrium dynamics in these materials.
Based on a quantum mechanic theory, we will investigate electron-electron, electron-phonon, and electron-photons interactions in graphene as well as exciton-phonon, exciton-exciton, and exciton-photon coupling in TMD materials and related heterostructures. The core of the theoretical model are Bloch equations, a couples system of differential equations allowing us to to resolve the non-equilibrium dynamics of optically excited electrons and excitons in time and energy. With the gained insights, we will be able to investigate the possibility to predict novel technological concepts in particular in the field of light, molecule and strain sensors. As a result, the proposed project is of great interest for both fundamental and application-oriented research.