Manipulation and Non-Linear Propagation of Excitonic Complexes in 2D Materials

Two-dimensional transition metal dichalcogenides offer an excellent platform to study non-linear dynamics of tightly-bound exciton quasiparticles. The properties of the excitons and their optical response change drastically in the presence of free charges, leading to emergence of many-body states described as trions or Fermi polarons. The physics of such Bose-Fermi quasiparticle mixtures have attracted a lot of interest in the scientific community and motivated the development of methods to control them on ultrafast time-scales. In addition, excitonic complexes are known to be mobile both in monolayers and heterostructures, with the transport of optical excitations playing a central role from both fundamental and technological perspectives.<br/>The first part of the talk will be focused on the use of intense THz pulses to transiently modify light-emission of exciton-electron ensembles in a monolayer semiconductor. We demonstrate a near complete, THz-induced trion-to-exciton conversion by monitoring time resolved photoluminescence after optical excitation. It offers new pathways to manipulate exciton-electron mixtures in monolayer semiconductors, triggering a non-linear optical response by low-energy photons on picosecond timescales. In the second part, I will discuss linear and non-linear propagation of interlayer excitons in atomically reconstructed heterobilayers for an extended density range up to the Mott transition. Key results include demonstration of rapid exciton diffusion in absence of disorder- and Moiré-induced localization, role of the exciton-exciton interactions, and effectively negative diffusivity in the regime of dissociated excitons and dense electron-hole plasma.