Strong Interactions Break Anderson Localization, Driving Segregation in One-Dimensional Fermi-Hubbard Systems

The behaviour of electrons in disordered materials typically leads to localisation, where they become trapped and unable to move freely, a phenomenon often strengthened by interactions between them. However, a team led by Ali Tozar from Hatay Mustafa Kemal University now demonstrates a surprising breakdown of this established principle. Their research reveals that strong interactions between electrons can actually overcome disorder, causing the system to segregate into distinct regions where electrons with different spin accumulate at opposite boundaries. While this boundary accumulation superficially resembles effects seen in non-reciprocal systems, the team rigorously proves this segregation arises from electrons minimizing their energy, not from any inherent directionality in the material, fundamentally changing our understanding of how disorder and interactions compete in these complex systems.

The team demonstrates that strong repulsive interactions can overcome the tendency of disorder to freeze particle movement, causing the system to transition into a phase where particles with opposing spins accumulate at opposite boundaries. This macroscopic segregation, while superficially resembling other boundary accumulation phenomena, arises from a fundamentally distinct mechanism, according to the analysis. By conducting rigorous control experiments, the researchers prove that this segregation persists even when certain conditions are removed, confirming the unique nature of the observed phenomenon.

Strong Interactions Overcome Disorder, Enable Segregation

This research investigates what happens when strong interactions combine with disorder in quantum systems. The central finding is that strong interactions can drive a system from being localized to a state where particles effectively separate into distinct regions. Crucially, the researchers demonstrate that this is not simply a consequence of other effects, but a fundamentally different process driven by energy minimization. They show that the observed segregation is a thermodynamic effect, not a topological one. This work has implications for understanding Many-Body Localization, a related phenomenon where interactions can prevent thermalization in disordered systems, and contributes to the broader field of open quantum systems, where systems interact with their environment.

Strong Interactions Defeat Anderson Localization in One Dimension

Scientists demonstrate a surprising breakdown of established principles governing disordered quantum systems. The research focuses on a model commonly used to understand interacting electrons in materials, subjected to disorder and specific hopping conditions. Contrary to expectations, the team observed a sharp transition into a phase where particles with opposing spins accumulate at opposite boundaries of the system. This macroscopic segregation occurs even with strong disorder, challenging the established understanding that disorder always leads to localization. Experiments reveal that this segregation persists even when certain conditions are removed, proving it is not a consequence of those conditions.

The primary driver of this segregation is a many-body energy minimization mechanism, where the system seeks its lowest energy state despite the disruptive influence of disorder. Measurements confirm a divergent energy susceptibility at the transition, indicating a fundamental shift in the system’s thermodynamic behaviour. This breakthrough delivers a new perspective on the interplay between disorder, interactions, and topology in open quantum systems.

Spin Segregation Driven by Strong Disorder

This research demonstrates a surprising breakdown of established principles governing disordered quantum systems. Scientists investigated the interplay between strong disorder and repulsive interactions in a one-dimensional model, revealing that interactions can overcome the tendency of disorder to localize particles. Contrary to expectations, the team found that strong interactions drive the system into a segregated phase where particles of opposite spin accumulate at opposite boundaries. This macroscopically observable segregation represents a new phenomenon in disordered systems, challenging the conventional understanding of disorder and interaction competition.

The team rigorously established that this segregation arises from the system’s drive to minimize energy, rather than from other effects previously associated with similar boundary accumulation phenomena. Through careful control experiments, they proved the segregation persists even without those effects, identifying energy minimization as the primary mechanism. The results demonstrate a sharp transition characterized by a divergent energy susceptibility, indicating a fundamental shift in the system’s behaviour.