Er2Ti2O7: Evidence of Order by Disorder in a Frustrated Quantum Antiferromagnet

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  • 1 December 2001
Abstract
Er2Ti2O7 is a realisation of the frustrated XY antiferromagnet on the pyrochlore lattice, for which theory predicts fluctuation-induced symmetry breaking in an otherwise highly degenerate ground state manifold. We present a theoretical analysis of the classical model compared to neutron scattering experiments on the real material, both below and above the ordering temperature, 1.173(2) K. We present strong evidence that the real system has order stabilised by zero-point quantum fluctuations that can be modelled by classical spin wave theory. The ordered moment is found to be massively suppressed to about a third of its classical value, which indicates strong quantum fluctuations, either local or global. It appears that the system is close to a quantum critical point. Inelastic neutron scattering and specific heat are consistent with this scenario.

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