Configuration-Controlled Many-Body Localization and the Mobility Emulsion*

We uncover a new non-ergodic phase, distinct from the full MBL phase, in a disordered two-leg ladder of interacting hardcore bosons. The dynamics of this emergent phase is determined by the many-body configuration of the initial state and features the coexistence of localized and extended many-body states at fixed energy density. We show that eigenstates in this phase can be described in terms of interacting emergent Ising spin degrees of freedom suspended in a mixture with inert charge-like degrees of freedom (doublons), and thus dub it a mobility emulsion (ME). We argue that grouping eigenstates by their doublon density reveals a transition between localized and extended states that is invisible as a function of energy density. We further demonstrate that the dynamics of the system following a quench may exhibit either thermalizing or localized behavior depending on the doublon density of the initial product state. These results establish a new paradigm for using many-body configurations as a tool to study and control nonergodic dynamics which can be realized in existing disordered Bose-Hubbard ladders.

Reference: arXiv:1808.05220 (to appear as an Editors' Suggestion in Physical Review B)