Floquet Physics in Atomically Thin 2D Semiconductors

Coherent interactions between light and matter can establish a versatile means to manipulate electronic bandstructures. This so-called ‘Floquet engineering’ is particularly interesting when applied to materials with inherently exceptional bandstructures, where it can enable quantum phase transitions or facilitate optical manipulation of coherent superpositions. However, a major limitation in previous works is determining if these processes are adiabatic, largely due to the absence of an established technique to measure coherent dynamics through the duration of the driving pulse. In this thesis, we explicitly excite and probe the coherent exciton dynamics in monolayer WS$_2$, a two-dimensional semiconducting transition metal dichalcogenide (TMDC). Multidimensional coherent spectroscopy (MDCS) is used to create the coherent superposition of inter-valley excitons, which are energetically degenerate but spin and momentum distinct, and probe the evolution of this coherence while using Floquet engineering to modify the bandstructure.