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Effet Josephson pour l'étude des supraconducteurs à haute température critique

Abstract : During this PhD work, we developed an original technique to make planar nano-Josephson junctions,both of fundamental and technological interest. Junctions are made in a YBa2Cu3O6+ film using standard microfabrication and ion irradiation techniques. From a fundamental point of view, we showed that the proximity effect plays an important role in the Josephson coupling. The results are interpreted within the theoretical framework of the quasiclassical Usadel equations. In addition to the fundamental interest of these structures, this technology represents several advantages to develop applications working at liquid nitrogen temperature. On the basis of this technique, we made dc SQUIDs which exhibit very good characteristics.
The second part of this PhD is dedicated to the study of pairing fluctuations in the pseudogap regime of underdoped cuprates by a Josephson-like experiment. The existence of pairing fluctuations is revealed by measuring the current-voltage characteristics of a Josephson junction in which one side of the junction is the underdoped superconductor above its Tc, while the other side is an optimally doped superconductor well below its own Tc. To realize this experiment, we developed a new technique to make trilayer microjunctions
(underdoped YBaCuO/PrBaCuO/optimally doped YBaCuO). At low temperature, when both electrodes are in the superconducting state, a Josephson behavior is observed. In the intermediate regime,
when one electrode is in the superconducting state and the other one in the pseudogap state, we observed a signature of pairing fluctuations in a temperature range of 15K above the transition temperature, which
is much lower than the characteristic temperature of the pseudogap (250K). This result is in favor of a classical scenario where the pairing fluctuations are limited to the vicinity of the transition.
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Contributor : Nicolas Bergeal <>
Submitted on : Wednesday, April 19, 2006 - 3:18:12 PM
Last modification on : Friday, October 23, 2020 - 4:37:26 PM
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Nicolas Bergeal. Effet Josephson pour l'étude des supraconducteurs à haute température critique. Supraconductivité [cond-mat.supr-con]. Université Pierre et Marie Curie - Paris VI, 2005. Français. ⟨tel-00012161⟩

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