Bose-Fermi $N$-polaron state emergence from correlation-mediated blocking of phase separation

TL;DR

This paper investigates how strong impurity-bath correlations in a one-dimensional Bose-Fermi mixture lead to the formation of an $N$-polaron state, preventing phase separation and causing impurity clustering and self-localization.

Contribution

It demonstrates the emergence of an $N$-polaron state due to correlation-mediated effects, revealing a transition from phase separation to impurity clustering in a 1D lattice system.

Findings

Formation of an $N$-polaron state replacing phase separation.

Impurity clustering driven by strong impurity-bath correlations.

Fermionic self-localization from a Mott insulator background.

Abstract

We study $N$ fermionic impurities in a one-dimensional lattice bosonic bath at unit filling. Using DMRG and mixed boundary conditions-periodic for bosons, open for fermions -- we find an $N$-polaron ground state replacing phase separation at high interspecies repulsion. This tightly bound state of clustered particles emerges due to strong impurity-bath correlations, which induce large impurity-impurity correlations that we quantify via the von Neumann entropy and bipartite mutual information, respectively. This system also reveals a fermionic self-localization effect from a Mott insulator background due to local correlations between the impurities and the bath. The growth of long-range correlations breaks this Mott phase, resulting in the transition to impurity clusters delocalized along the system. Finally, we show that there is a critical impurity number, which depends on intraspecies bosonic interaction, beyond which phase separation is recovered.