Wednesday, 19 April 2017
Dr Christopher Gies
Institute for Theoretical Physics
University of Bremen
"Tailoring Optical Properties of New Atomically Thin Semiconductors"
Atomically thin layers of transition-metal dichalcogenides, such as MoS2 have emerged in the wake of graphene as new class of optically active materials. Unlike graphene, they possess a direct band gap at the K valley of the band structure. Their fundamental optically active excitation is an electron-hole pair at the K valley, the excitonic properties of which are determined by the Coulomb interaction between them. However, most interaction lines do not pass the material itself, but lie outside of the thin layer, giving rise to an exciton binding energy in the range of 0.5 eV. This enables the external manipulation of the interaction and leads to the interesting prospect of creating nanostructures in a non-invasive way. Possible applications range from display technologies to the quantum-optical regime of single-photon sources. Optical properties further depend on the presence of excited carriers in the bands, where they lead to screening and phase-space filling effects. I will discuss absorption and photoluminescence properties of these fascinating materials on the basis of experiments and microscopic theory. Our approach combines abinitio electronic properties with semiconductor many-body calculations of optical transitions beyond the reach of typical GW/BSE methods.
WHEN: Monday 24 April 2017
WHERE: Room 314, Science 3 Building
TIME: 3.00 pm–4.00 pm
All interested are welcome to attend
Light refreshments to follow in Common Room