Boundary-obstructed topological phases

  title={Boundary-obstructed topological phases},
  author={Eslam Khalaf and Wladimir A. Benalcazar and Taylor L. Hughes and Raquel Queiroz},
  journal={arXiv: Mesoscale and Nanoscale Physics},
Symmetry protected topological (SPT) phases are gapped phases of matter that cannot be deformed to a trivial phase without breaking the symmetry or closing the bulk gap. Here, we introduce a new notion of a topological obstruction that is not captured by bulk energy gap closings in periodic boundary conditions. More specifically, we say two bulk Hamiltonians belong to distinct boundary obstructed topological `phases' (BOTPs) if they can be deformed to each other on a system with periodic… 
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