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Order by disorder spin wave gap in the XY pyrochlore magnet Er2Ti2O7.
K A Ross1, Y Qiu2, J R D Copley3
1Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA and NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
Physical Review Letters
|March 4, 2014
Summary
Researchers experimentally confirmed the "Order-by-Quantum-Disorder" mechanism in Er2Ti2O7, observing a spin wave gap crucial for selecting its magnetic ground state.
Area of Science:
- Condensed Matter Physics
- Quantum Magnetism
- Materials Science
Background:
- The antiferromagnetic XY pyrochlore Er2Ti2O7 exhibits complex magnetic behavior.
- Understanding ground state selection mechanisms in frustrated magnets is a key challenge.
- The
- Order-by-Quantum-Disorder
- (ObQD) mechanism proposes quantum fluctuations select magnetic order.
Purpose of the Study:
- To experimentally measure the spin wave excitation gap in Er2Ti2O7.
- To validate the predicted spin Hamiltonian and the ObQD mechanism.
- To investigate the temperature dependence of the spin gap.
Main Methods:
- Inelastic neutron scattering using low incident energies.
- Time-of-flight technique for measuring spin wave excitations.
- Analysis of magnetic ground state selection in Er2Ti2O7.
Main Results:
- A spin wave gap of Δ=0.053±0.006 meV was measured at the zone center.
- The experimental gap is consistent with theoretical predictions and heat capacity bounds.
- The gap magnitude scales with the square of the order parameter and vanishes at the Néel temperature (TN).
Conclusions:
- Experimental evidence strongly supports the ObQD mechanism in Er2Ti2O7.
- The measured spin gap confirms the robustness of the derived spin Hamiltonian.
- Quantum fluctuations play a critical role in determining the magnetic ground state of this material.
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