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Theses

Cohérence Quantique et Effet Kondo dans les Nanostructures

Abstract : Quantum coherence effects lie at the heart of mesoscopic physics: they control the behaviour of conductors which size becomes comparable to the electron phase coherence length Lf.
The experiments presented in this thesis deal with the effects of the phase coherence of electrons on the transport properties of metallic diffusive conductors.
We have first concerned ourselves with electron dephasing in measuring, at very low temperature, the weak localisation magnetoresistance of quasi-1D gold wires containing iron magnetic impurities. The measured behaviour of the electron phase coherence time tf is well described in the framework of Kondo impurities, by the interplay between the single impurity Kondo effect and the RKKY impurity-impurity interactions. This result is an important contribution to the debate about the low temperature saturation of tf.
Elsewhere, we have studied the quantum magnetoconductance oscillations, Altshuler-Aronov-Spivak (AAS) and Aharonov-Bohm (AB), in 2D networks of silver rings with different geometries. Notably, using a recent theory, we have extracted tf from the Fourier harmonics of the AAS oscillation. The measured temperature dependence, different from that extracted from a quasi-1D wire, suggests an effect of the topology on the dephasing. Finally, we have measured the size dependence of the amplitudes of both AB and AAS oscillations in networks of 10^6 to 10 loops: when one dimension of the network becomes smaller than Lf, the ensemble averaging of the quantum oscillations is non trivial, revealing that transport is dominated by subtle quantum interferences. This is a clear and convincing signature of the dimensional crossover leading to mesoscopic physics.
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Submitted on : Wednesday, August 8, 2012 - 2:12:31 PM
Last modification on : Friday, December 18, 2020 - 1:34:04 PM
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Félicien Schopfer. Cohérence Quantique et Effet Kondo dans les Nanostructures. Matière Condensée [cond-mat]. Université Joseph-Fourier - Grenoble I, 2005. Français. ⟨tel-00011250⟩

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