Interplay of disorder and interactions in a flat-band supporting diamond chain

Abstract: We systematically study the effect of disorder and interactions on a quasi-one dimensional diamond chain possessing flat bands. Disorder localizes all the single particle eigenstates, while at low disorder strengths we obtain weak flat-band based localization (FBL), at high disorder strengths, we see conventional Anderson localization (AL). The compactly localized (CL) eigenstates of flat bands show a persisting oscillatory recurrence in the study of single-particle wavepacket dynamics. For low disorder a damped oscillatory recurrence behavior is observed which is absent for high disorder. Non-interacting many particle fermion states also follow the same trend except showing a delocalizing tendency at intermediate disorder due to the fermionic statistics in the system. As interactions are switched on, for the finite-sizes that we are able to study, a non-ergodic `mixed phase' is observed at low disorder which is separated from the MBL phase at high disorder by a thermal phase at intermediate-disorder. A study of many-body nonequilibrium dynamics reinforces these findings.