Topological order in the insulating Josephson junction array.
We propose a Josephson junction array which can be tuned into an unconventional insulating state by varying external magnetic field. This insulating state retains a gap to half-vortices; as a consequence, such an array with nontrivial global geometry exhibits a ground state degeneracy. This degeneracy is protected from the effects of external noise. We compute the gaps, separating higher energy states from the degenerate ground state, and we discuss experiments probing the unusual properties of this insulator.
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Laboratoire de Physique Théorique et Hautes Energies, CNRS UMR 7589, Universités Paris 6 et 7, 4, place Jussieu, 75252 Paris Cedex 05, France.
Feigel'man
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Ioffe
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