Order by quantum disorder in Er2Ti2O7

Here we establish the systematic existence of a U(1) degeneracy of all symmetry-allowed Hamiltonians quadratic in the spins on the pyrochlore lattice, at the mean-field level. By extracting the Hamiltonian of Er(2)Ti(2)O(7) from inelastic neutron scattering measurements, we then show that the U(1)-d...

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Bibliographic Details
Published in:Physical review letters 2012-10, Vol.109 (16), p.167201-167201
Main Authors: Savary, Lucile, Ross, Kate A, Gaulin, Bruce D, Ruff, Jacob P C, Balents, Leon
Format: Article
Language:English
Subjects:
Condensed Matter
Physics
Strongly Correlated Electrons
Online Access:Get full text
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Summary:Here we establish the systematic existence of a U(1) degeneracy of all symmetry-allowed Hamiltonians quadratic in the spins on the pyrochlore lattice, at the mean-field level. By extracting the Hamiltonian of Er(2)Ti(2)O(7) from inelastic neutron scattering measurements, we then show that the U(1)-degenerate states of Er(2)Ti(2)O(7) 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 U(1) degeneracy in Er(2)Ti(2)O(7) 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.
ISSN:0031-9007
1079-7114
DOI:10.1103/PhysRevLett.109.167201