Generating Dirac mass by local symmetry breaking in SnTe topological crystalline insulator*

Topological phases of matter provide an exciting field of research and may be a key to future electronic devices. In a topological insulator, metallic electronic surface states (SS) are protected by time reversal symmetry. Topological crystalline insulators (TCIs) are a newer class of materials for which electronic SS are topologically protected by certain crystallographic symmetries. Breaking global crystal symmetry causes the SS to become gapped and non-metallic. But what happens when the crystal symmetry is broken locally?
Tin telluride (SnTe), a welknownTCI, shows gapless SS or Dirac fermions for its (001) & (111) surfaces. Our density functional calculations provide a detailed picture of how local symmetry breaking on SnTe (001) surfaces greatly suppresses topological surface states. We expect that in such symmetry broken regions, locally massive Dirac fermions are created. STM measurements on SnTe show that defects in the form of dislocations, vacancies, step edges and pits do exist and surface states are greatly suppressed in their vicinity (Adv. Mater. Inter., 4, 1601011 (2017)). By combining theory and experiment, we explain that it is possible to host both massive and massless Dirac Fermions on a single surface.