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Cohérence aux échelles mésoscopiques : réponse électromagnétique d'anneaux isolés et supercourants dans les nanotubes de carbone

Abstract : At mesoscopic scale and low temperature, the electronic wavefunctions, in a metallic sample, keep a well defined phase on the phase coherence length which is of the order of the size of the system. Electronic transport and thermodynamic properties of such systems are then modified by electronic interferences. In a ring geometry, because of the influence of magnetic flux on the phase of electronic wavefunctions, these corrections lead to a periodic behaviour versus the magnetic flux through the ring with a period determined by the flux quantum h/e. By coupling mesoscopic rings to a microresonator we show that the correction due to quantum coherence to the average electromagnetic response of bidimensionnal rings etched in a GaAs/GaAlAs heterojunction is dominated by the electric contribution. This latter quantity is positive at low field, which means that screening is enhanced when time reversal symetry is broken by magnetic field. The magnetic response is diamagnetic at low field. This sign was also measured on silver rings, which is not consistent with current theoretical predictions for orbital magnetism of rings. In order to test the possibility to induce coherent transport in carbon nanotubes, we have connected them to superconducting contacts. Our results on these junctions show that it is possible to have proximity induced superconductivity in such system. The measured critical current are surprisingly high compared to the expected value in SNS junctions with normal metal. These junctions also exhibit remarkable behaviour versus temperature or magnetic field.
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https://tel.archives-ouvertes.fr/tel-00002327
Contributor : Richard Deblock <>
Submitted on : Monday, January 27, 2003 - 9:48:24 AM
Last modification on : Wednesday, October 14, 2020 - 4:00:40 AM
Long-term archiving on: : Friday, April 2, 2010 - 6:45:40 PM

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  • HAL Id : tel-00002327, version 1

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Richard Deblock. Cohérence aux échelles mésoscopiques : réponse électromagnétique d'anneaux isolés et supercourants dans les nanotubes de carbone. Physique [physics]. Université Paris Sud - Paris XI, 2001. Français. ⟨tel-00002327⟩

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