Anderson localization and the topology of classifying spaces

TL;DR

This paper develops a topological framework to classify localized and delocalized phases of noninteracting fermions across all symmetry classes and dimensions, providing new insights into Anderson localization phenomena.

Contribution

It introduces a topological phase diagram approach based on Dirac mass topology, unifying and extending previous results for various symmetry classes and dimensions.

Findings

Reproduces known localization results across symmetry classes

Explains the even-odd effect in 1D chiral classes

Provides a topological understanding of density of states singularities

Abstract

We construct the generic phase diagrams encoding the topologically distinct localized and delocalized phases of noninteracting fermionic quasiparticles for any symmetry class from the tenfold way in one, two, and three dimensions. To this end, we start from a massive Dirac Hamiltonian perturbed by a generic disorder for any dimension of space and for any one of the ten symmetry classes from the tenfold way. The physics of Anderson localization is then encoded by a two-dimensional phase diagram that we deduce from the topology of the space of normalized Dirac masses. This approach agrees with previously known results and gives an alternative explanation for the even-odd effect in the one-dimensional chiral symmetry classes. We also give a qualitative explanation for the Gade singularity and Griffiths effects in the density of states using the first homotopy group of the normalized Dirac masses in two dimensions. Finally, this approach is used to analyze the stability of massless Dirac fermions on the surface of three-dimensional topological crystalline insulators.