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Étude des transitions de phases quantiques supraconducteur -- isolant, métal -- isolant dans des matériaux amorphes désordonnés proches de la dimension 2

Abstract : The understanding of the effect of disorder on the superconductivity remains a major issue in solid state physics. This problem involves the competition between the disordered-induced localization that leads to an insulator and the formation of the Cooper pairs that leads to an infinite conductivity. These effects are dramatic in dimension 2, the lower dimension for the existence of either a metal or a superconductor. The system is often described by a Superconductor -- Insulator Transition (SIT) and is interpreted as a Quantum Phase Transitions, that occur at and induced by a parameter crossing a critical value. Among these parameters, for example intrinsic to the system, we can cite the electronic density of state, the microscopical disorder and the thickness. The NbSi alloy is of great interest for the study of the SIT. The material is homogeneous and amorphous down to 2.5nm and up to 250 of annealing. We observed a SIT induced by the composition, the annealing and the thickness, that we compared to the fermionic theories (Finkel'stein) relying on the weakening of the superconductivity by disorder, and the bosonic theories (Dirty Boson Model, Fisher), relying on the Cooper pairs localization. Theses experiments undermine the idea that a unique parameter such as the sheet resistance or the product of the Fermi wave vector and the electron mean free path can describe all disorder. They especially outline the specific effect of the thickness. Moreover, we study the metallic state that appears at the lowest temperature between the superconductive and the insulating states, that contradicts the dogma according to which no metal can exist at 2D. The phase diagram we obtain with these samples is well interpreted with the Bose Metalconcept of Das Doniach. The NbSi is thus a promising system for an advance study of this new metallic state.
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https://tel.archives-ouvertes.fr/tel-00579256
Contributor : Olivier Crauste <>
Submitted on : Wednesday, March 23, 2011 - 11:02:00 PM
Last modification on : Wednesday, October 14, 2020 - 4:00:12 AM

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  • HAL Id : tel-00579256, version 2

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Olivier Crauste. Étude des transitions de phases quantiques supraconducteur -- isolant, métal -- isolant dans des matériaux amorphes désordonnés proches de la dimension 2. Supraconductivité [cond-mat.supr-con]. Université Paris Sud - Paris XI, 2010. Français. ⟨tel-00579256v2⟩

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