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Etude de reseaux de nanojonctions Josephson : competition entre le champ magnetique et la geometrie

Abstract : Josephson nanojunction arrays provide a suitable model to study many physical phenomena such as the Kosterlitz-Thouless-Berezinski transition for large capacity junctions, the superconductor-insulator quantum phase transition for very low capacity junctions, and also the competition between the magnetic field and the geometry of the underlying lattice. We have studied the phase diagram for a particular array called the dice network. When the magnetic flux per cell is equal to half a flux quantum, which corresponds to the magnetic frustration f=1/2, the electronic wave function is trongly localized in a finite space. This phenomenon results from the so-called Aharonov-bohm destructive interferences. The prediction of this effect led us up to make Al/Al2O3/Al nanojunction dice networks using electronic lithography. We performed magnetic imaging of the vortex structures using Bitter decoration, and also low-noise electrical measurements at very low temperature. The comparison between the pahse diagram at f=1/2 and f=0 let us identify two original phases of these networks for f=1/2. On one hand, in the superconducting state where quantum fluctuations are negligible, the observed vortex configuration doesn't shown any longe range order, correlation length is of the order of one lattice spacing. Moreover, our measurements of the critical current as a function of the frustration suggest the presence of a commensurate state. Although we did not observe any thermal hysteresis,all of these experimental results seem to exhibit a low temperature vortex glass phase. On the other hand, for networks with higher quantum fluctuations, we observe a low temperature resistive phase temperature independent, that is characteristic of a vortex quantum liquid phase.
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https://tel.archives-ouvertes.fr/tel-00007831
Contributor : Nathalie Le Moulec <>
Submitted on : Tuesday, December 21, 2004 - 4:06:39 PM
Last modification on : Friday, December 18, 2020 - 1:34:04 PM
Long-term archiving on: : Friday, April 2, 2010 - 9:26:34 PM

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  • HAL Id : tel-00007831, version 1

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Emmanuelle Serret. Etude de reseaux de nanojonctions Josephson : competition entre le champ magnetique et la geometrie. Supraconductivité [cond-mat.supr-con]. Université Joseph-Fourier - Grenoble I, 2002. Français. ⟨tel-00007831⟩

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