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Etude de supraconducteurs mésoscopiques par nanocalorimétrie

Abstract : Nanocalorimetric measurements have been carried out on systems composed of arrays of mesoscopic superconductors: aluminium rings and disks of size close to the aluminum coherence length at zero temperature ($\xi(0)\approx 160$ nm). We show that the heat capacity $C$ of these systems is modulated by a perpendicular applied magnetic field $H$; this is the first time that a thermal signature of the mesoscopic nature of such systems is reported. The shape, period, pseudo-period or amplitude of the observed modulations of $C$ depend on the size of the systems as well as on their geometry or topology. Far from the critical temperature, the oscillations of $C$ are due to the penetration or the expulsion of vortices, such as the fluxoid remains quantized in units of $\Phi_0=h/2e$, the superconducting flux quantum. Our measurements of $C$ can be understood in the framework of the Ginzburg-Landau theory; from this we learn that occupied states are mostly metastable ones, leading to unexpected periodicities of $C(H)$ and to interesting hysteretical features. Closer to the critical temperature, oscillations of $C(H)$ are attributed to the Little-Parks effect, i.e. the $\Phi_0$-periodical oscillation of the critical temperature of a ring or of a cylinder trapping a magnetic flux. The experiments we present are the first experimental demonstrations of this effect carried out on a mesoscopic sample without connecting it to electron reservoirs.
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https://tel.archives-ouvertes.fr/tel-00184585
Contributor : Florian Ong <>
Submitted on : Wednesday, October 31, 2007 - 2:05:57 PM
Last modification on : Thursday, November 19, 2020 - 1:01:01 PM
Long-term archiving on: : Monday, April 12, 2010 - 1:06:49 AM

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  • HAL Id : tel-00184585, version 1

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Florian Ong. Etude de supraconducteurs mésoscopiques par nanocalorimétrie. Supraconductivité [cond-mat.supr-con]. Université Joseph-Fourier - Grenoble I, 2007. Français. ⟨tel-00184585⟩

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