Quantum phase transition from a paramagnetic Anderson insulating state to a ferromagnetic many-body localized state via an intermediate ferromagnetic metallic phase

TL;DR

This paper investigates how electron correlations and spin degrees of freedom influence the transition from Anderson insulators to many-body localized states, revealing a complex phase diagram with ferromagnetic and metallic phases.

Contribution

It introduces a real-space spin-resolved Hartree-Fock-Anderson simulation approach to study the phase transition, uncovering a novel intermediate ferromagnetic metallic phase.

Findings

Weak correlations preserve paramagnetic Anderson insulator up to high temperatures.

Strong correlations induce ferromagnetism and metallicity at low temperatures.

Identifies a quantum phase transition involving paramagnetic insulator, ferromagnetic metal, and ferromagnetic MBL insulator.

Abstract

Effects of electron correlations on Anderson insulators have been one of the central themes for recent two decades, suggesting that the Anderson insulating phase turns into a novel insulating state referred to as many body localization (MBL). However, the role of spin degrees of freedom in this dynamical phase transition still remains unclarified as a function of the interaction strength. In this study, we perform real-space spin-resolved Hartree-Fock-Anderson simulations to investigate metal-insulator transitions above a critical disorder strength in three spatial dimensions, where all single-particle states are Anderson-localized without interactions. Here, relatively weak correlations below the Mott regime are taken into account in the mean-field fashion but disorder effects are introduced essentially exactly. We find two types of single-particle mobility edges, where the multifractal spectrum of the interaction-driven low-energy mobility edge deviates from that of the high-energy one smoothly connected with the multifractal spectrum of the metal-insulator transition without interactions. We show that the weakly interacting insulating phase remains to be a paramagnetic Anderson insulating state up to the temperature of the order of the band width. On the other hand, we uncover that the relatively strongly interacting insulating phase still below the Mott regime is ferromagnetic, which turns into a ferromagnetic metallic state at a critical temperature much lower than the order of the bandwidth. Based on all these results, we propose a quantum phase transition from a paramagnetic Anderson insulating state to a ferromagnetic MBL insulating phase via an intermediate ferromagnetic metallic state, which intervenes between these two insulators at the Fermi energy.