Flux expulsion and greedy bosons: frustrated magnets at large N
Abstract
We investigate the Sp(N) mean-field theory for frustrated quantum magnets. First, we establish some general properties of its solutions; in particular, for small spin we propose simple rules for determining the saddle points of optimal energy. We then apply these insights to the pyrochlore lattice. For spins on a single tetrahedron, we demonstrate a continuous ground state degeneracy for any value of the spin length. For the full pyrochlore lattice, this degeneracy translates to a large number of near-degenerate potential saddle points. Remarkably, it is impossible to construct a saddle point with the full symmetry of the Hamiltonian--at large N, the pyrochlore magnet CANNOT be a spin liquid. Nonetheless, for realistic finite values of N, tunnelling between the nearly degenerate saddle points could restore the full symmetry of the Hamiltonian.
Keywords
Cite
@article{arxiv.cond-mat/0408498,
title = {Flux expulsion and greedy bosons: frustrated magnets at large N},
author = {O. Tchernyshyov and R. Moessner and S. L. Sondhi},
journal= {arXiv preprint arXiv:cond-mat/0408498},
year = {2007}
}
Comments
4 pages, 2 eps figures