Mitch Conway, Swinburne
Coherent optical manipulation of electronic bandstructures via Floquet Engineering is a promising means to control quantum systems on an ultrafast timescale. However, the ultrafast switching on/off of the driving field comes with questions regarding the validity of the Floquet formalism, which is defined for an infinite periodic drive, and to what extent the transient changes can be driven adiabatically.
Using multidimensional coherent spectroscopy, we explicitly excite, control, and probe a coherent superposition of excitons in the K and K’ valleys in monolayer WS2. With a circularly polarized, red-detuned, pump pulse, the degeneracy of the excitons can be lifted and the phase of the coherence rotated.
We demonstrate phase rotations that exceed pi, and show that the total phase rotation depends on the total pump fluence in pump duration-dependent measurements. Finally, we will discuss some preliminary measurements with a blue-detuned pump, in a regime where monolayer TMDCs have been predicted to undergo a topological phase transition.
About the presenter
Mitchell Conway is currently a research associate working with Dr Jeff Davis’s ultrafast spectroscopy group at Swinburne University of Technology. Mitch recently completed his PhD project working on modifying the electronic band structure of 2D materials by driving non-equilibrium states to realise 2D Floquet topological insulators. This work has contributed to Research Theme 3 light-transformed materials.