Hopf-insulators

Pontrjagin's seminal topological classification of two-band Hamiltonians in three momentum dimensions is hereby enriched with the inclusion of a crystallographic rotational symmetry. The enrichment is attributed to a new topological invariant which …

Topological band theory studies the behavior of non-interacting electrons in solids that is protected by topological invariants and is therefore robust against system perturbations. Among many topics that are important for characterizing topological …