exchange symmetry of the toric code is realized locally through an exactly solvable Hamiltonian on a two dimensional lattice which has no lattice dislocations and their associated defect line. The Hamiltonian is still changed locally in selected sites where we wish to realize this anyon symmetry. We refer to these selected sites as defect sites in analogy with the usual lattice defects. The operators on the defect sites condense dyons of the toric code and are shown to support states which obey the fusion rules of Ising anyons just as the lattice dislocations thus achieving the transition to the Ising phase from the toric code phase. They can also be introduced in an entire region leading to an idea of non-localized defects. The method leads to a natural generalization for other Abelian groups where they help realize all the anyon exchange symmetries locally.

DOI: 10.48550/arxiv.1508.01399

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The global

e

m

The global

e

m

{S}_{3}

, the permutation group of three elements. Topological crystalline defects---dislocations and disclinations---change the anyon type of an orbiting quasiparticle. They exhibit multichannel order-dependent fusion rules and projective braiding operations. Their braiding and exchange statistics breaks modular invariance and violates the conventional spin-statistics theorem. We develop a framework to characterize these unconventional properties that originate from the semiclassical nature of defects.

\mathbb{Z}_2\times\mathbb{Z}_2

, inversion and time reversal symmetry. We use a modified version of the string order parameters proposed in [New Journal of Physics 21, 113016 (2019)], adapted to work beyond the framework of tensor networks, to capture the symmetry fractionalization pattern of the anyons. We show that this order parameter accurately captures the symmetry fractionalization in a direct Hamiltonian interpolation between the decorated and trivial toric codes, and in the presence of symmetry-preserving local magnetic fields and Ising interactions. We also observe how the condensation of an anyon that fractionalizes the symmetry forces the symmetry to spontaneously break at the phase transition. This notably changes the phase diagram of this Hamiltonian under parallel magnetic fields compared to the regular toric code since the condensation of charge and flux anyons drives the system to two distinct trivial phases, a symmetry broken phase and symmetric phase. Moreover, we provide a proof of spontaneous symmetry breaking from anyon condensation in the framework of projected entangled pair states.