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Nouvel étalonnage cryogénique en réflectométrie (0.2 à 18 GHz) et application à l'étude de la dynamique des vortex de supraconducteurs HTc proche de Tc

Abstract : The aim of this work was to study the vortex dynamics in thin films at the vortex solid to vortex liquid transition. This region in the phase diagram has only been scarcely studied by sweep frequency measurements up to 20 GHz. We present a new cryogenic broadband calibration method. Its performance is shown by validating the method using metallic microstrips and by comparison with a usually used calibration technique. The interprétation of the results is performed by an ac mean field and a scaling analysis near Tg. Whereas the mean field theory is unable to account for the found results concerning all the dependences (frequency and magnetic field) of the impedance per unit length , a scaling of the complex ac conductivity up to our highest measurement frequencies is possible. This is in clear contradiction to the crossover from a scaling to a mean field behaviour found in the literature. As the critical exponents change when switching on the magnetic field, the universality class of the transition changes. Finally a new feature in the imaginary part of the ac conductivity o2 is shown. For temperatures over a certain value near Tc, o2 increases with increasing frequency. This behaviour is observed for all magnetic fields, only the crossover temperature changes according to the changes in Tc with magnetic field. This phenomenon does not have a theoretical explanation yet.
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https://tel.archives-ouvertes.fr/tel-00004277
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Submitted on : Monday, January 26, 2004 - 2:51:34 PM
Last modification on : Friday, December 18, 2020 - 1:34:04 PM
Long-term archiving on: : Wednesday, September 12, 2012 - 12:50:09 PM

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  • HAL Id : tel-00004277, version 1

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Thomas Reuss. Nouvel étalonnage cryogénique en réflectométrie (0.2 à 18 GHz) et application à l'étude de la dynamique des vortex de supraconducteurs HTc proche de Tc. Supraconductivité [cond-mat.supr-con]. Université Joseph-Fourier - Grenoble I, 2000. Français. ⟨tel-00004277⟩

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