# One-particle-density-matrix occupation spectrum of many-body localized states after a global quench

## TL;DR

This paper investigates the occupation spectrum of the one-particle density matrix in many-body localized states after a global quench, revealing a nonthermal occupation profile and partial quasiparticle occupation influenced by initial conditions.

## Contribution

It demonstrates the absence of a Fermi-liquid-like discontinuity in the steady state occupation spectrum post-quench, linking it to the local structure of the initial density-wave state.

## Key findings

- Discontinuity in occupation spectrum is absent after a global quench.
- Occupation function remains strongly nonthermal despite Fermi-liquid-like features.
- Partial quasiparticle occupation can be tuned by initial state and described by an effective temperature.

## Abstract

The emergent integrability of the many-body localized phase is naturally understood in terms of localized quasiparticles. As a result, the occupations of the one-particle density matrix in eigenstates show a Fermi-liquid-like discontinuity. Here we show that in the steady state reached at long times after a global quench from a perfect density-wave state, this occupation discontinuity is absent, reminiscent of a Fermi liquid at a finite temperature, while the full occupation function remains strongly nonthermal. We discuss how one can understand this as a consequence of the local structure of the density-wave state and the resulting partial occupation of quasiparticles. This partial occupation can be controlled by tuning the initial state and can be described by an effective temperature.