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Resonant metallic states in driven quasiperiodic lattices

We consider a quasiperiodic Aubry-Andre (AA) model and add a weak time-periodic and spatially quasiperiodic perturbation. The undriven AA model is chosen to be well in the insulating regime. The spatial quasiperiodic perturbation extends the model into two dimensions in reciprocal space. For a spatial resonance which reduces the reciprocal space dynamics to an effective one-dimensional two-leg ladder case, the ac perturbation resonantly couples certain groups of localized eigenstates of the undriven AA model and turns them into extended metallic ones. Slight detuning of the spatial and temporal frequencies off resonance returns these states into localized ones. We analyze the details of the resonant metallic eigenstates using Floquet representations. In particular, we find that their size grows linearly with the system size. Initial wave packets overlap with resonant metallic eigenstates and lead to ballistic spreading.