Protected boundary states in gapless topological phases

Shunji Matsuura, Po Yao Chang, Andreas P. Schnyder, Shinsei Ryu

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125 Scopus citations

Abstract

We systematically study gapless topological phases of (semi-)metals and nodal superconductors described by Bloch and Bogoliubov-de Gennes Hamiltonians. Using K-theory, a classification of topologically stable Fermi surfaces in (semi-)metals and nodal lines in superconductors is derived. We discuss a generalized bulk-boundary correspondence that relates the topological features of the Fermi surfaces and superconducting nodal lines to the presence of protected zero-energy states at the boundary of the system. Depending on the case, the boundary states are either linearly dispersing (i.e. Dirac or Majorana states) or dispersionless, forming two-dimensional surface flat bands or one-dimensional arc surface states. We study examples of gapless topological phases in symmetry classes AIII and DIII, focusing in particular on nodal superconductors, such as nodal noncentrosymmetric superconductors. For some cases we explicitly compute the surface spectrum and examine the signatures of the topological boundary states in the surface density of states. We also discuss the robustness of the surface states against disorder.

Original languageEnglish (US)
Article number065001
JournalNew Journal of Physics
Volume15
DOIs
StatePublished - Jun 2013
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

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