Excitonic self-driven Floquet effects in ultrafast pump-probe and magneto-optical spectroscopy

Periodic driving renormalizes materials’ electronic structure into Floquet quasi-stationary states observable in optical and electron photoemission spectra. In excitonic materials, optical pumping creates a large population of coherent excitons, which not only modifies the material's optical properties but also creates a non-equilibrium electrion self-energy. This self-energy can acts as a quasi-periodic driving field persisting even after the initial pump pulse is gone, leading to a self-driven exciton Floquet effect. This effect manifests in a camel backing in the electronic bandstructure, which is predicted to be visible in time-resolved angle-resolved photoemission spectroscopy (TR-ARPES). In this work, we propose an alternative probe of the self-driven exciton Floquet effect through ultrafast transient absorption and magneto-optical spectroscopy. We utilize the first-principles time-dependent adiabatic GW (TD-aGW) approach to calculate the time-resolved transient absorption spectrum of monolayer MoS₂. Importantly, we notice that the exciton self-driven Floquet effects renormalize the magnetic response of excitons, suggesting a novel mean to characterize non-equilibrium coherent effects in pump-probe spectroscopy.