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Ordres cachés et magnétisme étudiés par spectroscopie Raman en conditions extrêmes

Abstract : New electronic phases, the so-called "exotic phases", where the order parameter isn’t clearly identified, sometimes appear at low temperature and/or under high pressure in the matter. This thesis focuses on the study by Raman spectroscopy of these exotic orders in the URu2Si2 and PrRu4P12 compounds and of the magnetism in the multiferroïc compound BiFeO3 . For this purpose, we developed a new Raman spectroscopy set-up probing very low energy excitations (1 meV) under high pressure (20 GPa) and at low temperature (3 K). In the PrRu4P12 skutterudite, we followed crystal field excitations and phonon modes under pressure up to 17 GPa. Our results confirm that the lattice dynamic is a side effect of the metal-insulator transition. However, they refute current theories that explain the electronic order’s evolution under pressure based on crystal field levels inversion. They underline the possible existence of magnetism under pressure. The URu2Si2 compound has been studied at room pressure and low temperature. We observe new signatures of the hidden order phase consisting of a very narrow excitation and a low energy gap, both only seen in the A2g symmetry. The study of the electronic response and of the lattice dynamic shows the influence of the anisotropy on the Kondo physics. Finally, combining Raman measurements under pressure at room temperature, numerical simulations and theoretical calculations, we provide a global understanding of BiFeO3’s magnetism through its various structural phases up to 12 GPa.
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https://tel.archives-ouvertes.fr/tel-01188925
Contributor : Jonathan Buhot Connect in order to contact the contributor
Submitted on : Friday, October 2, 2015 - 3:29:55 PM
Last modification on : Tuesday, December 8, 2020 - 10:21:16 AM
Long-term archiving on: : Sunday, January 3, 2016 - 10:58:52 AM

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  • HAL Id : tel-01188925, version 2

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Jonathan Buhot. Ordres cachés et magnétisme étudiés par spectroscopie Raman en conditions extrêmes. Physique [physics]. Université Paris Diderot-Paris 7 Sorbonne Paris Cité, 2015. Français. ⟨tel-01188925v2⟩

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