544 research outputs found
Fractionalization in an Easy-axis Kagome Antiferromagnet
We study an antiferromagnetic spin-1/2 model with up to third
nearest-neighbor couplings on the Kagome lattice in the easy-axis limit, and
show that its low-energy dynamics are governed by a four site XY ring exchange
Hamiltonian. Simple ``vortex pairing'' arguments suggest that the model
sustains a novel fractionalized phase, which we confirm by exactly solving a
modification of the Hamiltonian including a further four-site interaction. In
this limit, the system is a featureless ``spin liquid'', with gaps to all
excitations, in particular: deconfined S^z=1/2 bosonic ``spinons'' and Ising
vortices or ``visons''. We use an Ising duality transformation to express vison
correlators as non-local strings in terms of the spin operators, and calculate
the string correlators using the ground state wavefunction of the modified
Hamiltonian. Remarkably, this wavefunction is exactly given by a kind of
Gutzwiller projection of an XY ferromagnet. Finally, we show that the
deconfined spin liquid state persists over a finite range as the additional
four-spin interaction is reduced, and study the effect of this reduction on the
dynamics of spinons and visons.Comment: best in color but readable in B+
Kagome chiral spin liquid as a gauged U(1) symmetry protected topological phase
While the existence of a chiral spin liquid (CSL) on a class of spin-1/2
kagome antiferromagnets is by now well-established numerically, a controlled
theoretical path from the lattice model leading to a low energy topological
field theory is still lacking. This we provide via an explicit construction,
starting from reformulating a microscopic model for a CSL as a lattice gauge
theory, and deriving the low-energy form of its continuum limit. A crucial
ingredient is the realisation that the bosonic spinons of the gauge theory
exhibit a symmetry-protected topological (SPT) phase, which upon
promoting its global symmetry to a local gauge structure ("gauging")
yields the CSL. We suggest that such an explicit lattice-based construction
involving gauging of an SPT phase can be applied more generally to understand
topological spin liquids.Comment: 5+3 pages, 3+4 figure
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