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Les contacts atomiques : un banc d'essai pour la physique mésoscopique

Abstract : This thesis presents the results of electrical transport experiments, in particular in the superconducting state, through the smallest circuit elements one could imagine: contacts of just one or a few atoms between two metallic electrodes. Because of their small dimensions, electronic transport through atomic contacts is a quantum coherent process. In the general framework of mesoscopic physics, they can be viewed as scatterers of electronic waves, all their transport properties being determined by the set of transmission coefficients of their scattering eigenstates or conduction channels. Because this set is amenable to a complete experimental determination, atomic contacts are ideal mesoscopic systems in the sense that they allow for a quantitative comparison, with no adjustable parameter, of experimental results with theoretical predictions for a variety of transport phenomena. We have performed such a comparison for three of them. First, by integrating these contacts into a suitable dissipative circuit, we performed for the first time a controlled measurement of the Josephson supercurrent through one atom. Our measurements of the maximum supercurrent a contact can sustain are in quantitative agreement with the results of the modern theoretical description of the Josephson effect in terms of Andreev bound states localized at the contact. Second, we measured the shot noise of the finite voltage current in the superconducting state. Our results provide direct evidence that in this regime the current is carried by Multiple Andreev Reflection (MAR) processes, which transfer giant charge packets. The measured size of these packets is in quantitative agreement with the predictions of the fully quantum MAR theory. Finally, when a mesoscopic conductor is placed in series with a resistor, its differential conductance at small voltages and temperatures is reduced. This Coulomb blockade phenomenon is well known and understood for tunnel junctions. Using atomic contacts, we have addressed the mostly unexplored high transmission regime and found that the blockade disappears in the ballistic limit . These results are the first qualitative evidence for a recently predicted link between Coulomb blockade and shot noise.
Mots-clés : transport électrique
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Submitted on : Monday, April 29, 2002 - 12:08:19 PM
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  • HAL Id : tel-00001329, version 1

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Ronald Cron. Les contacts atomiques : un banc d'essai pour la physique mésoscopique. Physique [physics]. Université Pierre et Marie Curie - Paris VI, 2001. Français. ⟨tel-00001329⟩

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