Signature of Diabatic Transition of Dressed Excitons in Monolayer $\mathbf{WSe}_{\mathbf{2}}$

Under intense periodic driving by light, an electronic system is photon-dressed, leading to a strong modification of its energy structure depending on the light intensity. Such concept of photon-dressed states, in other words Floquet states, is considered as a promising way to manipulate material properties in ultrafast time scale [1]. So far, there have been many reports on characteristic energy structure changes of Floquet states in solids [2]–[4]. However, in real experiments, where ultrashort pulses are usually used, the above Floquet picture becomes an approximate one, and we need to consider the dynamics of Floquet states in both the adiabatic and non-adiabatic regime [5], [6]. Such dynamical aspects of Floquet state have not been experimentally investigated well.