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Spectroscopies à l'aide du rayonnement synchrotron appliquées aux systèmes fortement corrélés : Transition métal-isolant dans les oxydes de vanadium

Abstract : In this thesis, we have studied the electronic structure near the Fermi level and the influence of correlations in two strongly correlated materials displaying metal-insulator transition as a function of temperature, doping and pressure: (V(1-x)Crx)2O3 and VO2 vanadium oxides. We have combined different spectroscopies using synchrotron radiation: photoemission, X-ray absorption and inelastic scattering. These complementary techniques, which provide an overall picture of the low energy excitations, are sensitive to the changes occurring in the electronic structure across the transition. Direct comparison between experimental results and theoretical predictions allowed us to clarify the role of electronic correlations in transition mechanisms. In VO2, our analysis is consistent with the correlation assisted Peierls transition model. For the transition upon doping and temperature in (V(1-x)Crx)2O3, our results confirm the hypothesis of correlation induced crystal field enhancement. Investigation of thermodynamic parameters effects reveals a different mechanism under pressure, suggesting an interplay between structural and electronic degrees of freedom. Investigation of the quasiparticles behavior at surfaces demonstrates the existence of a surface dead layer below the surface where correlated electronic states behave differently. The characteristic length of the dead layer seems to be an intrinsic, bulk property of the system.
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Contributor : Fanny Rodolakis <>
Submitted on : Tuesday, February 16, 2010 - 11:46:05 AM
Last modification on : Wednesday, September 16, 2020 - 4:32:01 PM
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Fanny Rodolakis. Spectroscopies à l'aide du rayonnement synchrotron appliquées aux systèmes fortement corrélés : Transition métal-isolant dans les oxydes de vanadium. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2009. Français. ⟨tel-00456986⟩

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