Abstract
Pyrochlore systems are ideally suited to the exploration of geometrical frustration in three dimensions, and their rich phenomenology encompasses topological order and fractional excitations. Classical spin ices provide the first context in which it is possible to control emergent magnetic monopoles, and anisotropic exchange leads to even richer behaviour associated with large quantum fluctuations. Whether the magnetic ground state of Yb2Ti2O7 is a quantum spin liquid or a ferromagnetic phase induced by a Higgs transition appears to be sample dependent. Here we have determined the role of structural defects on the magnetic ground state via the diffuse scattering of neutrons. We find that oxygen vacancies stabilise the spin liquid phase and the stuffing of Ti sites by Yb suppresses it. Samples in which the oxygen vacancies have been eliminated by annealing in oxygen exhibit a transition to a ferromagnetic phase, and this is the true magnetic ground state.
Highlights
Pyrochlore systems are ideally suited to the exploration of geometrical frustration in three dimensions, and their rich phenomenology encompasses topological order and fractional excitations
By correlating our results with magnetic diffuse scattering we are able to determine the effect of structural disorder on the spin correlations, and to unambiguously identify the true magnetic ground state of Colour Space group Lattice parameter Yb1 Yb2 Ti O(1) O(2) x R RW
A comparison between quantum and classical numerical methods applied to Yb2Ti2O7 was presented in ref. 34, and the numerical linked cluster (NLC) expansion results differ from the classical Monte Carlo ones most strikingly by the change in (220) intensity
Summary
Pyrochlore systems are ideally suited to the exploration of geometrical frustration in three dimensions, and their rich phenomenology encompasses topological order and fractional excitations. Whether the magnetic ground state of Yb2Ti2O7 is a quantum spin liquid or a ferromagnetic phase induced by a Higgs transition appears to be sample dependent. The identification of different magnetic ground states for nominally stoichiometric samples clearly points towards the importance of low levels of structural disorder. This sample dependence is strongly reinforced in measurements of the heat capacity, where the existence of a sharp peak in the millikelvin range varies dramatically for different powder and single-crystal samples[11,17,18]. We have determined the defect structures in a range of oxygendepleted, stuffed and nominally stoichiometric single crystals using diffuse neutron scattering, which is sensitive to vacancies and displacements of oxygen ions. By correlating our results with magnetic diffuse scattering we are able to determine the effect of structural disorder on the spin correlations, and to unambiguously identify the true magnetic ground state of
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