Interaction-Induced Breakdown of Anderson Localization: Thermodynamic Segregation disguised as the Skin Effect

TL;DR

This paper reveals that strong repulsive interactions can break Anderson localization in a disordered Fermi-Hubbard chain, causing boundary spin segregation driven by energy minimization, distinct from the non-Hermitian skin effect.

Contribution

It demonstrates a novel interaction-induced boundary segregation in a disordered system, challenging the traditional view of localization and highlighting a thermodynamic crossover mechanism.

Findings

Strong interactions overcome disorder-induced localization.

Boundary spin species accumulate at opposite edges.

Segregation persists without non-reciprocity, driven by energy minimization.

Abstract

We investigate the interplay between strong disorder and repulsive interactions in the one-dimensional Fermi-Hubbard model under open boundary conditions. While uncorrelated disorder is widely accepted to localize all single-particle eigenstates, a phenomenon typically reinforced by interactions in the Many-Body Localization (MBL) regime, we report a counter-intuitive breakdown of this paradigm. We demonstrate that strong repulsive interactions can overcome disorder-induced localization, driving the system into a macroscopically segregated phase where spin species accumulate at opposite boundaries. Although this boundary accumulation phenomenologically mimics the Non-Hermitian Skin Effect (NHSE) observed in non-reciprocal systems, our comprehensive analysis reveals a fundamentally different origin. By performing a rigorous control experiment in the Hermitian limit, we prove that the segregation persists without non-reciprocity, identifying many-body energy minimization as the primary driver. This "interaction-induced segregation" manifests as a sharp thermodynamic crossover, characterized by a divergent energy susceptibility, challenging the conventional understanding of disorder-interaction competition in open quantum systems.