Thursday, Mar 6, 12 p.m. 11 FLOOR OF THE GAMOW TOWER
B. Normand
EPF Lausanne, Switzerland
High-dimensional fractionalisation and spinon deconfinement in pyrochlore antiferromagnets
Spin S = 1/2 Klein models on the checkerboard and pyrochlore lattices contain in their ground-state manifold the subspace generated by the set of singlet dimer coverings, and thus possess an extensive ground-state degeneracy. Among the many exotic consequences is the presence of deconfined fractional excitations (spinons) which propagate through the entire system. While a realistic electronic model on the pyrochlore lattice is close to the Klein point, this point is in fact inherently unstable because any perturbation e restores spinon confinement at T = 0. Deconfinement is recovered in the finite-temperature region e << T << J, where the deconfined phase can be characterised as a dilute Coulomb gas of thermally excited spinons. The zero-temperature phase diagram away from the Klein point is analysed by means of a variational approach based on the singlet dimer coverings of the pyrochlore lattices and taking into account their nonorthogonality.