The focus of the III-V spectroscopy group, led by C. Schneider, is set on the investigation of light-matter coupled systems. Of particular interest are microcavities with integrated low dimensional materials, such as semiconductor quantum dots, quantum wells, or novel monolayer materials. The activities are thus subdivided into the field of Polaritonics, and quantum optics with semiconductor quantum dots, and spectroscopy of novel two-dimensional semiconductors.
High quality microcavities with embedded quantum wells allow for investigation of strong coupling between excitons and photons. This light-matter hybridization gives rise to new quasiparticles, the so-called exciton polaritons. Their energy momentum dispersion E(k) can be measured directly by angle resolved spectroscopy. Polaritons are bosons and can undergo a condensation process at rather high temperatures (up to ~ 100 K in GaAs). III-V semiconductors offer the unique possibility to excite these condensates not only optically but also electrically. Our current research interests include optimization of electrically driven polariton condesates, detailed studies of their coherence properties, and the fabrication of advanced polaritonic devices.
The potential landscapes of microcavity polaritons can be engineered by means of nanotechnology. In our group, we study the behaviour of these hybrid particles in complex lattices, which carry the potential to emulate complex quantum systems in a controlled manner. As a simple example, we can arrange sites with localized polaritons in square lattice structures, and observe the evolution of a distinct band structure resulting from site-to-site evanescent coupling of the localized polariton mode wavefunctions.
Quantum Dot spectroscopy
Solid state quantum dots (QDs) are promising sources of single and indistinguishable photons which are the key to applications e.g. in quantum information science or linear optical quantum computing. Furthermore, QDs are a suitable platform for a spin-photon-interface due to their ability to store a single electron or hole spin after a charged exciton complex radiatively decays.
In our group, we investigate the emission properties of III/V-QDs which are often embedded in microcavities. Due to the coupling of the QD to the optical mode, one can either achieve an enhancement of the spontaneous emission when the QD is in the weak coupling regime or study light-matter interaction of strongly coupled QD-cavity systems.
One of the primary targets of our QD activities is the realization and demonstration of an ultimately bright and coherent single photon source, based on coupled quantum dot-microcavity systems. Such a source, which emits exactly one single photon with Fourier limited bandwidth per excitation pulse will open entirely new pathways in quantum photonics.
Transition metal dichalcogenides (TMD), such as MoS2, MoSe2 and WSe2 exhibit an indirect bandgap in bulk material, yet they become direct bandgap semiconductors in the monolayer limit. Simlilar to graphene, such atomic monolayers can be produced by simple exfoliation techniques. The unique combination of huge exciton binding energies, large Bohr radii and peculiar spinor properties explains the rising interest in this new class of semiconductors. In our group, we investigate the possibilities to exploit these properties for high temperature polaritonics. We furthermore study exciton localization in such monolayer crystals with respect to their application as novel solid state single photon sources.