Absence of Thermalization in Finite Isolated Interacting Floquet Systems

TitleAbsence of Thermalization in Finite Isolated Interacting Floquet Systems
Publication TypeJournal Article
Year of Publication2018
AuthorsSeetharam, K, Titum, P, Kolodrubetz, M, Refael, G
JournalPhysical Review B
Date Published2018/01/29

Conventional wisdom suggests that the long time behavior of isolated interacting periodically driven (Floquet) systems is a featureless maximal entropy state characterized by an infinite temperature. Efforts to thwart this uninteresting fixed point include adding sufficient disorder to realize a Floquet many-body localized phase or working in a narrow region of drive frequencies to achieve glassy non-thermal behavior at long time. Here we show that in clean systems the Floquet eigenstates can exhibit non-thermal behavior due to finite system size. We consider a one-dimensional system of spinless fermions with nearest-neighbor interactions where the interaction term is driven. Interestingly, even with no static component of the interaction, the quasienergy spectrum contains gaps and a significant fraction of the Floquet eigenstates, at all quasienergies, have non-thermal average doublon densities. We show that this non-thermal behavior arises due to emergent integrability at large interaction strength and discuss how the integrability breaks down with power-law behavior in system size.