Marginal Anderson localization and many body delocalization

TL;DR

This paper investigates how weak interactions destabilize marginally localized systems, such as disordered topological insulators, leading to delocalization and challenging the stability of quantized Hall conductance at finite energies.

Contribution

It demonstrates that marginal localization is generally unstable under interactions if the critical exponent /d, providing a theoretical argument against stabilizing quantized Hall conductance at non-zero energy density.

Findings

Weak interactions induce delocalization in marginally localized systems.

Marginal localization is unstable if /d, based on the Harris/Chayes bound.

Quantized Hall conductance cannot be stabilized at finite energy density.

Abstract

We consider d dimensional systems which are localized in the absence of interactions, but whose single particle (SP) localization length diverges near a discrete set of (single-particle) energies, with critical exponent \nu. This class includes disordered systems with intrinsic- or symmetry-protected- topological bands, such as disordered integer quantum Hall insulators. In the absence of interactions, such marginally localized systems exhibit anomalous properties intermediate between localized and extended including: vanishing DC conductivity but sub-diffusive dynamics, and fractal entanglement (an entanglement entropy with a scaling intermediate between area and volume law). We investigate the stability of marginal localization in the presence of interactions, and argue that arbitrarily weak short range interactions trigger delocalization for partially filled bands at non-zero energy density if \nu \ge 1/d. We use the Harris/Chayes bound \nu \ge 2/d, to conclude that marginal localization is generically unstable in the presence of interactions. Our results suggest the impossibility of stabilizing quantized Hall conductance at non-zero energy density.