Exciton-driven Floquet engineering from first principles

Floquet engineering uses periodic driving to tailor electronic structures and material properties out of equilibrium. Excitons offer a distinct route to this control: their electron-hole dynamics can act as an internal drive, enabling Floquet engineering beyond direct laser dressing. A microscopic description of this regime requires simultaneous access to excitonic dynamics and their momentum-resolved photoemission signatures, which remains challenging in realistic materials. Here we develop an efficient first-principles framework combining real-time time-dependent density functional theory with a modified long-range-corrected exchange-correlation kernel, Floquet-band analysis, and time- and angle-resolved photoemission simulations. Using monolayer hexagonal boron nitride as a benchmark, we capture a subgap excitonic resonance and show that the resulting oscillatory excitonic field generates clear Floquet sidebands and band renormalization, even without temporal overlap between pump and probe pulses. Our approach establishes a practical and computationally efficient route for predicting nonequilibrium Floquet phenomena driven by collective excitations in quantum materials.