Creating Bloch-Floquet states with partially coherent driving fields

In the field of Floquet engineering, one seeks to control material properties on ultrafast timescales by driving the system with a time-periodic external electromagnetic field. Such periodic perturbations break the continuous time symmetry and lead to the formation of replicas of energy bands – analogous to the broken spatial translation symmetry in crystals. Through manipulating the frequency and intensity of the driving field, it is possible to engineer unusual properties of matter, ranging from photo-driven magnetism and superconductivity to topological phase transitions. A promising new strategy to engineer Floquet states which circumvents the problem of heating, typically associated with photo-driven systems, is to utilize an internal time-dependent oscillation of the system, such as phonons or excitons. In this talk we examine to what extent an oscillating coupling field with finite temporal coherence, like that produced by a thermal bath of bosons, can drive Floquet phenomena. Through a combination of model and ab initio real-time simulations, we demonstrate the conditions over which Floquet physics can be observed with partially coherent driving fields, an important step towards engineering long-lived Floquet phenomena in real materials.