Strong Bloch-Floquet effects driven by excitonic fields in monolayer transition metal dichalcogenides from a time-dependent GW approach

A long-sought goal in condensed-matter physics is to create nontrivial phases of matter by optically driving materials out of equilibrium. Within the Bloch-Floquet formalism, a system driven by a perturbation with period T experiences a coupling of bands separated by energies multiple of ?(2π/T) and proportional to the intensity of the external field. Although most experimental realizations of Bloch-Floquet physics have been realized with strong optical fields, recent theoretical works have proposed the utilization of other bosonic fields, such as phonons, magnons, and excitons, as external periodic driving fields. In this work, we present first-principles calculations of Bloch-Floquet effects in a transition metal dichalcogenide (TMD) monolayer using a recently develop time-dependent GW method. Contrary to the optically driven case, we observe strong band renormalizations and hybridization effects even for moderate exciton concentrations. We explain this uniquely strong effect in 2D materials in light of their strong exciton binding energy, and efforts towards the experimental interpretation of such a signal from time-resolved angle-resolved photoemission spectroscopy (TR-ARPES). We also connect our work with recent discussions regarding non-equilibrium excitonic insulators and condensates.