In-gap band formation in a periodically driven charge density wave insulator

Modern time-resolved spectroscopy experiments on quantum materials raise the question, how strong electron-electron interactions, in combination with periodic driving, form unconventional transient states. Here we show using numerically exact methods that in a driven strongly interacting charge-density-wave insulator a band-like resonance in the gap region is formed. We associate this feature to the so-called Villain mode in quantum-magnetic materials, which originates in moving domain walls induced by the interaction. We do not obtain the in-gap band when driving a non-interacting charge density wave model. In contrast, it appears in the interacting system also in equilibrium at intermediate temperatures and in the short-time evolution of the system after a quantum quench to the lowest-order high-frequency effective Floquet Hamiltonian. Our findings connect the phenomenology of a periodically driven strongly correlated system and its quench dynamics to the finite-temperature dynamical response of quantum-magnetic materials and will be insightful for future investigations of strongly correlated materials in pump-probe setups. The interplay of strong electronic interactions and periodic driving leads to new effects in nonequilibrium quantum-many body systems. The authors find an in-gap band, which is due to moving domain walls, similar to the so-called Villain-mode of quantum magnets.