QUASIPARTICLES IN A DIFFUSIVE CONDUCTOR:
INTERACTION AND PAIRING

S. Gueron 1
1 QUANTRONICS - Quantronics Group
SPEC - UMR3680 - Service de physique de l'état condensé, IRAMIS - Institut Rayonnement Matière de Saclay
Abstract : The first part of the thesis is concerned with quasiparticle-quasiparticle interaction in diffusive films, that is films with an elastic mean free path much smaller than the film dimensions. In such films, the interaction is expected to be greater than in perfect metals, which are described by the Landau theory of Fermi liquids. We have measured at low temperature the energy distribution function in several diffusive mesoscopic wires (a few micrometers long), placed out-of-equilibrium. Depending on the ratio between the diffusion time across the wire and the interaction time, the distribution function is typical of a non-interacting regime, a strongly thermalized regime, or an intermediate regime. From the intermediate regime one can infer the energy dependence of the modulus of the interaction.
The second part of the thesis is concerned with the proximity effect, that is the penetration in a non-superconducting (normal N) metal of superconducting (S) order, characterized by pair correlations between quasiparticles. The penetration of pair correlations in the normal metal modifies its density of states (DOS). We have measured this DOS at several distances from the interface with a superconductor: 100 nm away, the DOS at the Fermi energy is reduced by a factor two. The modification of the DOS persists as far as one micrometer into the normal metal.
The subgap or Andreev current through a NS interface is another property which depends on the pair correlations induced in the normal metal. This current, which is due to the coherent passage of two electrons from the N metal into the S, is enhanced by confinement of the quasiparticle trajectories near the NS interface. In order to demonstrate the interferential origin of this enhancement, we have implemented an « NS-QUID », made of a superconducting fork, closed by a normal mesoscopic wire. The interference pattern corresponds to the current through the device, which is modulated by a perpendicular magnetic field.
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Submitted on : Monday, November 5, 2007 - 11:01:25 PM
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  • HAL Id : tel-00185371, version 1

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S. Gueron. QUASIPARTICLES IN A DIFFUSIVE CONDUCTOR:
INTERACTION AND PAIRING. Condensed Matter [cond-mat]. Université Pierre et Marie Curie - Paris VI, 1997. English. ⟨tel-00185371⟩

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