Extended topological group structure due to average reflection symmetry

We extend the single-particle topological classification of insulators and superconductors to include systems in which disorder preserves average reflection symmetry. We show that the topological group structure of bulk Hamiltonians and topological defects is exponentially extended when this additional condition is met and examine some of its physical consequences. Those include localization–delocalization transitions between topological phases with the same boundary conductance as well as gapless topological defects stabilized by average reflection symmetry. (paper)