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Transport et cohérence quantique dans les nanocircuits hybrides supraconducteur-métal

Abstract : In this work, we study how the conductance of a mesoscopic-scale normal metal circuit is modified by the action of a superconductor. First we describe different existing theories, and then we present very low temperature (down to 20 mK) measurements demonstrating the non-local effects appearing in the conductance of the normal metal induced by the superconductivity. We show that the metallic conductance is strongly energy dependant, and that the energy scale is the Thouless energy. In an Aharonov-Bohm geometry, interference experiments demonstrate the long range quantum coherence of electron pairs (2e) in the normal metal. The experimental results are explained in detail in the framework of the quasiclassical Green's functions theory. Comparison with theory shows the important influence of the reservoir-like external parts of the sample. We present a novel technology allowing the fabrication on hybrid Niobium-Copper mesoscopic structures. In order to control the formation of oxide barriers, we developed an Ultra-High-Vacuum valve extracting pure Oxygen from the ambient air. A C++ program is described used for the calculation of the conductance of any hybrid circuit made of normal and superconducting metal. When two superconductors, connected through a normal metal, are held at a constant voltage, the a.c. Josephson effect modulates the energy-dependant density of states in the normal metal. We propose an experiment which will evidence the influence of the variations of the density of states on the transport properties of the electrons.
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Submitted on : Monday, April 9, 2007 - 7:12:22 PM
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  • HAL Id : tel-00140666, version 1




Pierre Charlat. Transport et cohérence quantique dans les nanocircuits hybrides supraconducteur-métal. Supraconductivité [cond-mat.supr-con]. Université Joseph-Fourier - Grenoble I, 1997. Français. ⟨tel-00140666⟩



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