Prof. Nic Shannon （東京大学大学院新領域創世科学研究科）
"Cyclic exchange, isolated states and spinon deconfinement in the XXZ Heisenberg model on a checkerboard lattice"
The antiferromagnetic Ising model on a checkerboard lattice has an ice--like ground state manifold with extensive degeneracy and, to leading order in $J_{xy}$, deconfined spinon excitations. We explore the role of cyclic exchange arising at finite $J^2_{xy}/J_z$ on the ice states and their associated spinon excitations. By mapping the original problem onto an equivalent quantum six--vertex model, we identify three different phases as a function of the chemical potential for flippable plaquettes --- a phase with long range N\'eel order, a non--magnetic state of resonating square plaquettes, and a quantum disordered phase with gapped but deconfined spinon excitations. We identify for the first time the role of ``isolated states'' with no flippable plaquettes in supporting fractionalization on the pyrochlore lattice, and make connection with existing work on quantum dimer and isotropic Heisenberg models.
http://arxiv.org/abs/cond-mat/0403729