Atypical energy eigenstates in the Hubbard chain and quantum disentangled liquids

TL;DR

This paper explores special non-thermal eigenstates in the Hubbard chain that exhibit quantum disentangled liquid behavior, revealing atypical states with lower entropy density and implications for ergodicity breakdown in quantum systems.

Contribution

It demonstrates the existence of atypical energy eigenstates with QDL behavior in the Hubbard model, extending understanding of non-thermal states in integrable systems.

Findings

Existence of finite energy eigenstates with QDL behavior.

Thermal states show a weaker QDL property in a specific temperature range.

Atypical states have lower entropy density than thermal states at the same energy.

Abstract

We investigate the implications of integrability for the existence of quantum disentangled liquid (QDL) states in the half-filled one-dimensional Hubbard model. We argue that there exist finite energy-density eigenstates that exhibit QDL behaviour in the sense of J. Stat. Mech. P10010 (2014). These states are atypical in the sense that their entropy density is smaller than that of thermal states at the same energy density. Furthermore, we show that thermal states in a particular temperature window exhibit a weaker form of the QDL property, in agreement with recent results obtained by strong-coupling expansion methods in arXiv:1611.02075. This article is part of the themed issue `Breakdown of ergodicity in quantum systems: from solids to synthetics matter'.