Condensed Matter Theory Seminar | May 22, 14:00
Defects and Majorana modes in the Kitaev honeycomb model
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).
MPI-PKS
Seminar Room TP 0.03
Contact: Maria Hermanns