Abstract
Here we establish the systematic existence of a degeneracy of all symmetry-allowed Hamiltonians quadratic in the spins on the pyrochlore lattice, at the mean-field level. By extracting the Hamiltonian of from inelastic neutron scattering measurements, we then show that the -degenerate states of are its classical ground states, and unambiguously show that quantum fluctuations break the degeneracy in a way which is confirmed by experiment. The degree of symmetry protection of the classical degeneracy in is unprecedented in other materials. As a consequence, our observation of order by disorder is unusually definitive. We provide further verifiable consequences of this phenomenon, and several additional comparisons between theory and experiment.
- Received 5 April 2012
DOI:https://doi.org/10.1103/PhysRevLett.109.167201
© 2012 American Physical Society