Particle dynamics and ergodicity-breaking in twisted-bilayer optical lattices

Recent experiments have realized a twisted bilayer-like optical potential for ultra-cold atoms, which in contrast to solid-state set ups may allow for an arbitrary ratio between the inter- and intra-layer couplings. For commensurate Moiré twistings a large-enough inter-layer coupling results in particle transport dominated by channel formation. For incommensurate twistings, the interlayer coupling acts as an effective disorder strength. Whereas for weak couplings the whole spectrum remains ergodic, at a critical value part of the eigenspectrum transitions into multifractal states. A similar transition may be observed as well as a function of an energy bias between the two layers. Our study reveals atoms in optical twisted-bilayer lattices as an interesting new platform for the study of ergodicity breaking and multifractality.