Diffusive metal in a percolating Chern insulator

TL;DR

This paper demonstrates that geometric disorder, such as bond dilution with flux insertions, can induce a robust diffusive metallic phase in a Chern insulator with particle-hole symmetry, contrasting with typical localization in disordered fermionic systems.

Contribution

It reveals that geometric disorder can create a stable metallic phase in a Chern insulator, highlighting a new mechanism for metallicity in topological systems.

Findings

Metallic phase emerges with bond dilution and flux insertions.

Transport shows charge and anomalous Hall currents.

Different critical exponents for topological transition and metal-insulator transition.

Abstract

Two-dimensional non-interacting fermions without any anti-unitary symmetries generically get Anderson localized in the presence of disorder. In contrast, topological superconductors with their inherent particle-hole symmetry can host a thermal metallic phase, which is non-universal and depends on the nature of microscopic disorder. In this work, we demonstrate that in the presence of geometric disorders, such as random bond dilution, a robust metal can emerge in a Chern insulator with particle-hole symmetry. The metallic phase is realized when the broken links are weakly stitched via concomitant insertion of $\pi$ fluxes in the plaquettes. These nucleate low-energy manifolds, which can provide percolating conduction pathways for fermions to elude localization. This diffusive metal, unlike those in superconductors, can carry charge current and even anomalous Hall current. We investigate the transport properties and show that while the topological insulator to Anderson insulator transition exhibits the expected Dirac universality, the metal insulator transition displays a different critical exponent $\nu \approx 2$ compared to a disordered topological superconductor, where $\nu \approx 1.4$. Our work emphasizes the unique role of geometric disorder in engineering novel phases and their transitions in topological quantum matter.