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arXiv · 1802.03780

Spontaneous decay of a soft optical phonon in the relaxor ferroelectric PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$

C. Stock·P. M. Gehring·R. A. Ewings·G. Xu·J. Li·D. Viehland·H. Luo
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Abstract

We report the spontaneous decay of a soft, optical phonon in a solid. Using neutron spectroscopy, we find that specific phonon lifetimes in the relaxor PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$ are anomalously short within well-defined ranges of energy and momentum. This behavior is independent of ferroelectric order and occurs when the optical phonon with a specific energy and momentum can kinematically decay into two acoustic phonons with lower phase velocity. We interpret the well-known relaxor "waterfall" effect as a form of quasiparticle decay analogous to that previously reported in quantum spin liquids and quantum fluids.

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C. Stock, P. M. Gehring, R. A. Ewings, G. Xu, J. Li, D. Viehland, H. Luo. 2018-02-11. Spontaneous decay of a soft optical phonon in the relaxor ferroelectric PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$. https://doi.org/10.1103/physrevmaterials.2.024404

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