On the possibility of many-body localization in a doped Mott insulator

TL;DR

This paper demonstrates a disorder-free many-body localization phenomenon in a doped Mott insulator, driven by a novel Berry phase effect, with localized excitations forming due to strong interactions.

Contribution

It reveals a new mechanism for many-body localization without disorder, based on a Berry phase in a doped Hubbard model, supported by numerical simulations.

Findings

Localized droplet excitations form in a doped Mott insulator

MBL eigenstates can be constructed from separated localized droplets

Transition from MBL to quasiparticle phase by tuning Berry phase

Abstract

Many-body localization (MBL) is currently a hot issue of interacting systems, in which quantum mechanics overcomes thermalization of statistical mechanics. Like Anderson localization of non-interacting electrons, disorders are usually crucial in engineering the quantum interference in MBL. For translation invariant systems, however, the breakdown of eigenstate thermalization hypothesis due to a \emph{pure} many-body quantum effect is still unclear. Here we demonstrate a possible MBL phenomenon without disorder, which emerges in a lightly doped Hubbard model with very strong interaction. By means of density matrix renormalization group numerical calculation on a two-leg ladder, we show that whereas a single hole can induce a very heavy Nagaoka polaron, two or more holes will form bound pair/droplets which are all localized excitations with flat bands at low energy densities. Consequently, MBL eigenstates of finite energy density can be constructed as composed of these localized droplets spatially separated. We further identify the underlying mechanism for this MBL as due to a novel `Berry phase' of the doped Mott insulator, and show that by turning off this Berry phase either by increasing the anisotropy of the model or by hand, an eigenstate transition from the MBL to a conventional quasiparticle phase can be realized.