Acoustic anomaly and the Landau free energy of incommensurate K2SeO4

Gen Li, N. Tao, Le Van Hong, H. Z. Cummins, C. Dreyfus, M. Hebbache, R. M. Pick, J. Vagner

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


Brillouin-scattering studies of the longitudinal-acoustic mode propagating along the c* axis of K2SeO4 were performed in the vicinity of the incommensurate phase transition in both 90°and 180°scattering geometries. A theoretical derivation of the complex elastic constant C33() was carried out within the mean-field approximation including both bilinear (Landau-Khalatnikov) coupling to the amplitude mode, and anharmonic fluctuation contributions from the 2 soft mode above TI and from pairs of amplitude modes and phase modes below TI. Comparison between theory and the Brillouin data led to an excellent fit using free-energy parameters close to values deduced from previous static and dynamical experiments. Our measurements also indicate that the phason gap (0) is at least 100 GHz.

Original languageEnglish (US)
Pages (from-to)4406-4425
Number of pages20
JournalPhysical Review B
Issue number7
StatePublished - 1990
Externally publishedYes

ASJC Scopus subject areas

  • Condensed Matter Physics


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