Topologically-protected metallic states induced by a one-dimensional   extended defect in a 2D topological insulator
  We report ab initio calculations showing that a single one-dimensional extended defect can originate topologically-protected metallic states in the bulk of two-dimensional topological insulators. We find that a narrow extended defect composed of periodic units consisting of one octogonal and two pentagonal rings embedded in the hexagonal bulk of a bismuth bilayer introduces two pairs of one-dimensional Dirac-fermion states with opposite spin-momentum locking. Although both Dirac pairs are localized along the extended-defect core, their interactions are screened due to the trivial topological nature of the extended defect. 
E. N. Lima, T. M. Schmidt, and R. W. Nunes
cond-mat.mtrl-sci cond-mat.mes-hall cond-mat.other quant-ph