SPring-8, the large synchrotron radiation facility

Date&Time: 16:00, 17 Feb 2004

Speaker: Dr. Karlo Penc
Affiliation: Research Institute for Solid State Physics, Budapest, Hungary

Abstract
　　The quarter-filled Hubbard model extended with nearest neighbor repulsion on the pyrochlore lattice is an insulator for sufficiently large couplings, with an extensive ground state degeneracy. The model can be mapped to the ice- and the 6-vertex problems.
　　The large degeneracy in the ground state manifold can support topological excitations with e/2 charge. Quantitative results are presented for the two-dimensional bosonic version of the problem, the XXZ Heisenberg model, where we discuss the effect of quantum fluctuations and the spinon deconfinement.