# Phonons in the multiferroic langasite Ba3NbFe3Si2O14 : evidences for symmetry breaking

Abstract : The chiral langasite Ba$_3$NbFe$_3$Si$_2$O$_{14}$ is a multiferroic compound. While its magnetic order below T$_N$=27 K is now well characterised, its polar order is still controversial. We thus looked at the phonon spectrum and its temperature dependence to unravel possible crystal symmetry breaking. We combined optical measurements (both infrared and Raman spectroscopy) with ab initio calculations and show that signatures of a polar state are clearly present in the phonon spectrum even at room temperature. An additional symmetry lowering occurs below 120~K as seen from emergence of softer phonon modes in the THz range. These results confirm the multiferroic nature of this langasite and open new routes to understand the origin of the polar state.
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https://hal.archives-ouvertes.fr/hal-01186067
Contributor : Sophie de Brion <>
Submitted on : Tuesday, August 25, 2015 - 11:33:24 AM
Last modification on : Wednesday, September 15, 2021 - 2:56:02 PM
Long-term archiving on: : Thursday, November 26, 2015 - 1:51:42 PM

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### Citation

C. Toulouse, M. Cazayous, Sophie de Brion, Florence Lévy-Bertrand, H. Barkaoui, et al.. Phonons in the multiferroic langasite Ba3NbFe3Si2O14 : evidences for symmetry breaking. Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2015, 92 (10), pp.104302. ⟨10.1103/PhysRevB.92.104302⟩. ⟨hal-01186067⟩

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