# The Broad Brillouin Doublet and CP of Ktao\_3 : Second Sound vs. Two-Phonon Difference Scattering

Source: [The Broad Brillouin Doublet and CP of Ktao\_3 : Second Sound vs. Two-Phonon Difference Scattering](<https://www.sota2.com/research/paper/68fa1e2f7a2b558e29320832>)

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Data updated: 2025-10-23T14:14:57.578Z

Authors: E. Farhi, A.K. Tagantsev, B. Hehlen, R. Currat, L.A. Boatner, E.Courtens

Published: 2000-09-01T12:13:57.000Z

## Abstract

Low-T Brillouin spectra of the incipient ferroelectric KTaO3 exhibit a broad central peak (CP), and additional Brillouin doublets (BD), that can both be related to phonon-density fluctuations. On the basis of new high-resolution neutron data obtained of low-lying phonon branches, we analysed the phonon-kinetics mechanisms that are possibly the origin of these unusual features. Firstly, transverse acoustic (TA) phonons whose normal damping is faster than the BD frequency can produce hydrodynamic second sound. Secondly, two-phonon difference scattering from low damping thermal transverse phonons contribute to the spectra with either a sharp or a broader doublet, depending on the phonon group velocity and anisotropy of dispersion surfaces. The position of the observed sharp doublet is consistent with both mechanisms, but a comparison of the computed and experimental anisotropies favours the second process.

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## Original sources and implementation

[Original paper](<https://arxiv.org/abs/cond-mat/0009011>)

[PDF](<https://arxiv.org/pdf/cond-mat/0009011.pdf>)