Nucleation of ergodicity by a single mobile impurity in supercooled insulators

TL;DR

This paper demonstrates that a single mobile impurity can induce thermalization in a disordered insulator, revealing how ergodicity can emerge in localized systems through resonant processes involving the impurity.

Contribution

It introduces a mechanism where a single impurity acts as an ergodic seed, causing thermalization in localized insulators, supported by analytical and numerical evidence.

Findings

A single impurity can thermalize localized particles at weak disorder.

The critical disorder strength depends on particle density.

Doublons can thermalize mesoscopic systems but eventually localize due to conserved quantities.

Abstract

We consider a disordered Hubbard model, and show that, at sufficiently weak disorder, a single spin-down mobile impurity can thermalize an extensive initially localized system of spin-up particles. Thermalization is enabled by resonant processes which involve correlated hops of the impurity and localized particles. This effect indicates that certain localized insulators behave as "supercooled" systems, with mobile impurities acting as ergodic seeds. We provide analytical estimates, supported by numerical exact diagonalization (ED), showing how the critical disorder strength for such mechanism depends on the particle density of the localized system. In the $U\rightarrow\infty$ limit, doublons are stable excitations, and they can thermalize mesoscopic systems by a similar mechanism. The emergence of an additional conservation law leads to an eventual localization of doublons. Our predictions apply to fermionic and bosonic systems and are readily accessible in ongoing experiments simulating synthetic quantum lattices with tunable disorder.