Research goals

(a) Schematic illustration of graphene bandstructure including the scattering process leading to the carrier multiplication (CM). (b) Van der Waals heterostructure (Nature 499, 419 (2013)). (c) Hybrid nanostructure consisting of functionalized graphene.
(a) Schematic illustration of graphene bandstructure including the scattering process leading to the carrier multiplication (CM). (b) Van der Waals heterostructure (Nature 499, 419 (2013)). (c) Hybrid nanostructure consisting of functionalized graphene.

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) nanomaterials including graphene and transition metal dichalcogenides (TMDs) into the focus of current research. They represent a new class of materials that are characterized by a wide range of exceptional optical, electronic, mechanical, chemical, and thermal properties suggesting technological application in next-generation flexible and transparent nanoelectronic devices.

 

Graphene exhibits an unique electronic bandstructure with linear bands and no bandgap at the Dirac point. This results in novel relaxation channels for excited electrons that can e.g. lead to the appearance of the technologically relevant carrier multiplication (CM), cf. Fig. (a). The advantage of TMDs with molybendum disulfide (MoS2) as their most prominent representative lies in the direct bandgap, the strong exciton physics, and the possibility of vertical stacking to van der Waals bound heterostructures, cf. Fig. (b).  Since graphene and TMDs consist of single atom layers, they show a high sensitivity to changes in their surrounding, which makes them ideal candidates for chemical sensors, cf. Fig. (c).

 

The applied density matrix formalism offers tools to reveal the optical finger print of different atomically thin 2D materials. Furthermore, it allows us to microscopically track the way of optically excited carriers towards equilibrium  – resolved in time, momentum, and angle. The comparison with modern high-resolution experiments leads to new insights into the underlying elementary processes.

We are interested in particular in the following topics:

  • Optical fingerprint of atomically thin materials including graphene and transition metal dichalcogenides
  • Ultrafast carrier relaxation dynamics driven by carrier-carrier, carrier-phonon, and carrier-photon scattering
  • Exciton dynamics in TMDs
  • Exciton-molecule interaction in molecule-functionalized nanomaterials
  • Elementary processes behind photo-emission, photo-amplification, and photo-detection
  • Terahertz dynamics close to the Dirac point in graphene
  • Magneto-optics and inter-Landau-level dynamics in Landau-quantized graphen