76 research outputs found
Structure factor of low-energy spin excitations in a S=1/2 kagome antiferromagnet
The ground state of the S=1/2 Heisenberg antiferomagnet on kagome can be
viewed as a collection of fermionic spinons bound into small, heavy singlet
pairs. Low-energy magnetic excitations in this system correspond to breaking
the pairs into individual spinons. We calculate the structure factor for
inelastic neutron scattering from independent spinon pairs.Comment: 9 pages. Revised in response to referee reports. References adde
Unified theory of spin and charge in a ferromagnet
We derive a unified theory of spin and charge degrees of freedom in a
ferromagnet. The spin-transfer torque and spin electromotive force are examined
from the coarse-grained perspective of collective coordinates. The resulting
equations of motion reflect a balance of conservative, gyroscopic
(Berry-phase), and dissipative forces. We then expand the space of collective
coordinates by adding the electric charge. The adiabatic spin-transfer torque
and spin emf turn out to be a gyroscopic force; their nonadiabatic counterparts
are a dissipative force.Comment: Minor revision in response to referee comment
Unpaired Majorana modes on dislocations and string defects in Kitaev's honeycomb model
We study the gapped phase of Kitaev's honeycomb model (a spin liquid)
on a lattice with topological defects. We find that some dislocations and
string defects carry unpaired Majorana fermions. Physical excitations
associated with these defects are (complex) fermion modes made out of two
(real) Majorana fermions connected by a gauge string. The quantum state
of these modes is robust against local noise and can be changed by winding a
vortex around one of the dislocations. The exact solution respects gauge
invariance and reveals a crucial role of the gauge field in the physics of
Majorana modes. To facilitate these theoretical developments, we recast the
degenerate perturbation theory for spins in the language of Majorana fermions.Comment: 15 pages, 7 figures; added a brief history of twists, references, and
clarified the count of the topological degeneracy of the ground stat
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