



01311nas a2200157   4500008004100000245004900041210004900090260001500139490000700154520083300161100002100994700002501015700002001040700002501060856006801085       2017                        eng d00aExactly soluble model of boundary degeneracy0 aExactly soluble model of boundary degeneracy  c2017/01/250 v953 a<p>We investigate the topological degeneracy that can be realized in Abelian fractional quantum spin Hall states with multiply connected gapped boundaries. Such a topological degeneracy (also dubbed as &quot;boundary degeneracy&quot;) does not require superconducting proximity effect and can be created by simply applying a depletion gate to the quantum spin Hall material and using a generic spin-mixing term (e.g., due to backscattering) to gap out the edge modes. We construct an exactly soluble microscopic model manifesting this topological degeneracy and solve it using the recently developed technique [S. Ganeshan and M. Levin, Phys. Rev. B 93, 075118 (2016)]. The corresponding string operators spanning this degeneracy are explicitly calculated. It is argued that the proposed scheme is experimentally reasonable.</p>1 aGaneshan, Sriram1 aGorshkov, Alexey, V.1 aGurarie, Victor1 aGalitski, Victor, M.  uhttp://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.045309