Periodically driven, or Floquet, disordered quantum systems have
generated many unexpected discoveries of late, such as the anomalous
Floquet Anderson insulator and the discrete time crystal. Here, we
report the emergence of an entire band of multifractal wavefunctions in
a periodically driven chain of non-interacting particles subject to
spatially quasiperiodic disorder. Remarkably, this multifractality is
robust in that it does not require any fine-tuning of the model
parameters, which sets it apart from the known multifractality of
critical wavefunctions. The multifractality arises as
the periodic drive hybridises the localised and delocalised sectors of
the undriven spectrum. We account for this phenomenon in a simple random
matrix based theory. Finally, we discuss dynamical signatures of the
multifractal states, which should betray their presence in cold atom
experiments. Such a simple yet robust realisation of multifractality
could advance this so far elusive phenomenon towards applications, such
as the proposed disorder-induced enhancement of a superfluid
transition.
Chaos and Statistical Relaxation in Quantum Systems of Interacting Particles
