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DY: Dynamik und Statistische Physik

DY 11: Poster I

DY 11.12: Poster

Tuesday, March 18, 1997, 14:30–17:30, F

Low-energy dynamics of a frustrated antiferromagnet with extensive ground state degeneracy — •Roderich Moessner and John T. Chalker — Theoretical Physics, Oxford University, 1 Keble Road, GB–Oxford OX1 3NP

We study the low-energy dynamics of a classical Heisenberg antiferromagnet on various geometrically frustrated lattices, including, in particular, the pyrochlore lattice. These systems are of interest because they have many ground states which are not related by simple symmetry operations, and because they have many soft excitation modes.

In detail, the pyrochlore lattice is made up of corner-sharing tetrahedra. Each tetrahedron contributes four degrees of freedom to the system, constrained by the (three) conditions that its total spin be zero in the ground state: the degeneracy of the ground state is extensive.

Such systems have recently been studied in inelastic neutron scattering [1] and muon-spin resonance [2] experiments and they have been found to display unusual fluctuations at low temperatures.

The question we consider is how the ground state manifold is explored at small but finite temperatures. We discuss the nature of the ground state manifold, showing that there are no energy barriers dividing different portions of it, and examine how anhamonic interactions couple spin wave fluctuations to the zero modes of the system.

[1] M.J. Harris et. al., Phys. Rev. Phys. B52, R707 (1995)

[2] M.J. Harris et. al., to be published