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Fluctuations temporelles quantiques du courant dans des nanostructures

Abstract : In a mesoscopic conductor, the transport of current is coherent : the associated wave of the electrons keeps a well defined phase, so that one can observe interference effects. Transport in this regime has been extensively studied in the last decade, and the main features are well un-derstood. In this thesis, we did focus on another aspect of the quantume transport, the noise. The purpose is to detect the fluctuations of the current around its average value. Our work is divided in three parts : first, we have measured shot noise in a quantum point contact. Shot-noise is due to the granularity of the charge. In a classical conductor, it is directly related to the current. We have shown that in a quantum conductor, such as a quantum point contact, quantum correlation due to the Pauli principle reduce the shot-noise, and that it can even be suppressed under certain conditions. In a second part, we did use the fact that shot-noise is sensitive to the charge of the car-riers to detect the fractionally charged quasiparticles of the quantum Hall effect. The existence of the quasiparticles has been predicted since 1983, but no experimental observation has been reported up to now. By inducing a current of quasiparticles between the two edges of a sample in the fractional quantum Hall effect regime, and by measuring the noise associated with this current, we have proved it to be SI=2(e/3)I. This is actually a direct measurement of the charge of the carriers in the fractionnal quantum Hall regime, which is found to be e*=e/3 as predicted by the theory. Finally, the third part of our work is devoted to a subject closer to the applied physics, namely the measurement of low frequency noise in quantum dots. As quantum systems are more and more studied for potential applications, it is crucial to caracterize the low frequencuy noise (« 1/f » noise).We have found that this is due to free charges moving on the substract around the dot, and that any improvement of the noise of such systems goes through an improvement of the wafers.
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https://tel.archives-ouvertes.fr/tel-00006368
Contributor : Laurent Saminadayar <>
Submitted on : Monday, July 5, 2004 - 5:46:05 PM
Last modification on : Monday, February 10, 2020 - 6:12:21 PM
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Laurent Saminadayar. Fluctuations temporelles quantiques du courant dans des nanostructures. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 1997. Français. ⟨tel-00006368⟩

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