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Confinement quantique dans les nanocristaux supraconducteurs et transport électronique dans les réseaux de nanocristaux métalliques

Abstract : A first part of this thesis presents the development of a new synthesis of highly monodispersed populations of superconducting Lead nanocrystals. This synthesis enables us to measure precisely the superconducting thermodynamics properties as function of the size of the nanocrystals. We report on magnetic susceptibility measurements of the amplitude of the Meissner effect in these superconducting Lead nanocrystals as function of their diameter. Within the size range 10 < D < 30 nm, we find that the Meissner effect amplitude is order of magnitude smaller than expected from Ginzburg-Landau theory and is totally quenched for particles diameter below 16 nm, when the electronic spectrum becomes discrete. This shows that quantum confinement effects alter the Meissner superfluid response even at sizes scales significantly larger than expected from Anderson limit, i.e. the lower size limit for the existence of Cooper pairs in nanocrystals. A second part of this thesis presents a study of electronic transport in bidimensionnal arrays of Gold nanocrystals realized by the Langmuir technique. We report on the evolution of the electrical and optical conductivity of these arrays as function of the coupling between the nanocrystals by alkanedithiols chains with different lengths. We show that the conductivity of the array increases strongly when the length of alkane chains is reduced but no signature of metallic behavior is visible. Transport measurements at low temperature (4K) show non-linear I-V characteristics with a threshold voltage VT. These arrays exhibit a Coulomb blockade that can be analyzed by Middleton andWingreen model which identify the crossover between the insulator and the conductor states with a second order phase transition. In the vicinity of the critical point VT , the current follows a power law as function of the voltage applied as expected theoretically. The value of the exponent suggests that the transport of the electrons is dominated by co-tunneling processes.
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Submitted on : Tuesday, February 15, 2011 - 3:44:45 PM
Last modification on : Tuesday, January 25, 2022 - 12:46:02 PM
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  • HAL Id : pastel-00566233, version 1


Helena Moreira. Confinement quantique dans les nanocristaux supraconducteurs et transport électronique dans les réseaux de nanocristaux métalliques. Optique [physics.optics]. Paris 6, 2009. Français. ⟨pastel-00566233⟩



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