Floquet dynamics of disordered bands with isolated critical energies

TL;DR

This paper studies how periodic driving affects localization in disordered systems with isolated critical energies, revealing that topological protection can sustain delocalized states under strong drive, unlike non-topological models.

Contribution

It demonstrates that topologically protected extended states persist and are enhanced under strong periodic drive, contrasting with non-topological models where states become localized.

Findings

Topologically protected models retain delocalized states under strong drive.

Non-topological models localize entirely with weak drive.

Driving can enhance the spectral range of delocalized modes in topological systems.

Abstract

We investigate the localization properties of driven models that exhibit a sub-extensive number of extended states in the static setting. We consider instances where the extended modes are or are not protected by topological considerations. To this end, we contrast the strongly driven disordered lowest Landau level, which we refer to as the random Landau model (RLM), with the random dimer model (RDM); the latter also has a sub-extensive set of delocalized modes in the middle of the spectrum whose origin is not topological. We map the driven models on to a higher dimensional effective model and numerically compute the localization length as a function of disorder strength, drive amplitude and frequency using the recursive Green's function method. Our numerical results indicate that in the presence of a strong drive (low frequency and/or large drive amplitude), the topologically protected RLM continues to exhibit a spectrum with both localized and delocalized (or critical) modes, but the spectral range of delocalized modes is enhanced by the driving. This occurs due to an admixture of the localized modes with extended modes arising due to the topologically protected critical energy in the middle of the spectrum. On the other hand, in the RDM, a weak drive immediately localizes the entire spectrum. This occurs in contrast to the naive expectation from perturbation theory that mixing between localized and delocalized modes generically enhances the delocalization of all modes. Our work highlights the importance of the origin of the delocalized modes in the localization properties of the corresponding Floquet model.