Chiral Topological Phases and Fractional Domain Wall Excitations in One-Dimensional Chains and Wires

According to the general classification of topological insulators, there exist one-dimensional chirally (sublattice) symmetric systems that can support any number of topological phases. We introduce a zigzag fermion chain with spin-orbit coupling in magnetic field and identify three distinct topological phases. Zero-mode excitations, localized at the phase boundaries, are fractionalized: two of the phase boundaries support $\pm $e/2 charge states while one of the boundaries support $\pm $e and neutral excitations. In addition, a finite chain exhibits $\pm $e/2 edge states for two of the three phases. We explain how the studied system generalizes the Peierls-distorted polyacetylene model and discuss possible realizations in atomic chains and quantum spin Hall wires.