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Kitaev's honeycomb model [1] is a quantum spin liquid, celebrated for both the richness of its physical features, and the fact that it admits an exact solution. The latter can be cast in terms of Majorana fermions living in the background of a static Z_2 gauge field. The gapped phase of this model exhibits Z_2 topological order, equivalent to that of the toric code. Its ground state is a featureless spin liquid whose nontrivial properties can be revealed by introducing lattice defects. In the talk I will show that certain kinds of lattice dislocations and bond defects in this originally Abelian system carry unpaired Majorana fermions [2,3]. Each pair of such defects gives rise to a non-local physical fermion mode, i.e. a topologically-protected qubit, made out of two Majorana modes connected by a Z_2 gauge string. The qubit's composition reveals the crucial role of the emergent gauge field, neglected in most treatments of the Kitaev model, in the physics of Majorana modes. I will demonstrate how the non-local fermion can be created or annihilated by winding a magnetic vortex around a defect. [1] A. Kitaev, Ann. Phys. 321, 2 (2006). [2] O. Petrova, P. Mellado, O. Tchernyshyov, Phys. Rev. B 88, 140405 (2013). [3] O. Petrova, P. Mellado, O. Tchernyshyov, Phys. Rev. B 90, 134404 (2014).

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Olga Petrova, MPI-PKS
Seminar Room TP 0.03
Contact: Maria Hermanns