Research: Many-Body delocalization via emergent symmetry

Quantum many-body systems typically thermalize. There are, however, some examples, in which thermalization is violated. Strong violation of  thermalization occurs in the well-known many-body localized (MBL) systems, where all the states in the spectrum are non-thermal. A violation in the weaker sense occurs through the phenomenon of quantum many-body scars which are fewer states in the spectrum that violate thermalization. In this work we show that an emergent symmetry in a single eigenstate of a disordered model can protect it from MBL, while not preventing the rest of the states in the spectrum from many-body localizing. Hence, this is an example of weak violation of MBL due to the existence of non-MBL states in a spectrum of localized states. Furthermore, this study motivates how such an example calls for exploring "inverted quantum scars", namely, non-area law states embedded in a sea of localized states.

 N. S. Srivatsa, R. Moessner, A. E. B. Nielsen,
Many-body delocalization via emergent symmetry,
Phys. Rev. Lett. 125, 240401 (2020)