Green's function zeros — points where the propagator vanishes rather than diverges — have emerged as topological features in interacting systems. In static (equilibrium) systems, Green's function zeros require interactions: the vanishing of the propagator comes from many-body correlations that can't arise in a free system.
König and Mitra (arXiv:2602.21199) show that Floquet systems — systems driven periodically in time — can have Green's function zeros without interactions. The periodic drive alone creates zeros that would require correlations in a static setting. The drive substitutes for the interactions.
The zeros contribute to the topological invariant. This means the topology of a Floquet system can differ from any static system with the same symmetry class — not because it has different poles (the familiar band structure) but because it has zeros that static systems can't support without interactions. The topological classification expands.
The mechanism: periodic driving folds the energy spectrum into a Floquet Brillouin zone, creating new gap structures at the zone boundaries. These gaps can host zero-modes of the Green's function — points where the spectral weight vanishes rather than accumulates. In the static limit, such vanishing requires destructive interference from many-body correlations. In the Floquet case, the periodic drive provides the interference for free.
The general observation: a periodically driven system can mimic the effects of interactions without being interacting. The drive provides structure that, in equilibrium, would require many-body correlations. Time-periodicity is a resource that substitutes for complexity.