Disorder-Induced Topological Phases in a Two-Dimensional Chern Insulator with Strong Magnetic Disorder

TL;DR

This paper reveals that strong magnetic disorder can induce genuinely new topological phases in a 2D Chern insulator, characterized by disorder-driven transitions and phases with nontrivial topology absent in the clean system.

Contribution

It demonstrates that strong disorder can create topological phases in a Chern insulator that are disconnected from the clean limit, using numerical methods and Green's function analysis.

Findings

Disorder induces topological phases not connected to the clean limit.

Transitions between phases are driven by zeros of the Green's function.

Identifies a strong-coupling phase with nontrivial topology despite zero Chern number.

Abstract

Strong directional disorder in local magnetic moments coupled to a Chern insulator gives rise to topological phases that cannot be continuously connected to the clean limit and are therefore genuinely disorder-driven. We demonstrate this in a spinful Qi-Wu-Zhang model of a two-dimensional Chern insulator coupled to disordered classical spins of unit length. The topological phase diagram is computed numerically using two complementary approaches: twisted boundary conditions and the topological Hamiltonian technique. Our results show that strong disorder can act as a fundamental topological mechanism rather than merely a perturbation. For strong exchange coupling, tuning the mass parameter reveals a transition between phases with different Chern numbers $C$. Remarkably, this transition is driven by zeros, rather than poles, of the disorder-averaged Green's function crossing the chemical potential, and has no analogue in any clean system. We further identify a strong-coupling phase with $C = 0$ that is nonetheless topologically nontrivial, characterized by a distinct Chern number $C^{(\mathrm{S})} \neq 0$ over the manifold of classical spin configurations. This phase is also disorder-driven, as $C^{(\mathrm{S})} = 0$ in the clean limit.