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Electronic refrigeration using superconducting tunnel junctions

Abstract : In the recent years, nano-refrigeration using electron tunneling in hybrid Normal metal - Insulator - Superconductor (N-I-S) junctions has gained increasing attention. Its basic principle is the energy selective tunneling due to the presence of an energy gap in the superconductor density of states. With a sub-gap voltage bias, only the most energetic electrons can tunnel out of the normal metal, leaving behind the electrons with less energy. We have measured with a high resolution the differential conductance of S-I-N-I-S junctions, whose analysis gives us an access to the normal metal electronic temperature as a function of the voltage. A quantitative model is proposed, that includes the electron-phonon coupling and the Kapitza resistance at the interface with the substrate. With this model, we have achieved a thorough description of the charge and heat currents. We have also shown that the normal metal phonon temperature drops significantly below the substrate temperature. At very low temperature (T < 200mK) and low bias, the phase coherent Andreev current dominates the quasi-particle current. By analyzing quantitatively the heat balance in the S-I-N-I-S junction, we demonstrate that the Andreev current does carry heat. This thermal contribution heats the normal metal electrons, overriding over a large voltage range the tunneling-based cooling. The electronic cooling at an optimal bias (V ~ 2Delta/e) in a S-I-N-I-S junction is a known pending issue. Cooling effect in S-I-N-I-S junction is accompanied by the injection of hot quasi-particles in the S electrodes. We have proposed a simple model for the diffusion of excess quasi-particles in a superconducting strip with an external trap junction. The diffusion model has a complete analytic solution and predicts the minimum attainable temperature of the coolers.
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https://tel.archives-ouvertes.fr/tel-00371431
Contributor : Bernard Pannetier <>
Submitted on : Friday, March 27, 2009 - 6:49:36 PM
Last modification on : Thursday, November 19, 2020 - 1:01:00 PM
Long-term archiving on: : Thursday, June 10, 2010 - 7:02:52 PM

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  • HAL Id : tel-00371431, version 1

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CNRS | NEEL | UJF | UGA

Citation

Sukumar Rajauria. Electronic refrigeration using superconducting tunnel junctions. Superconductivity [cond-mat.supr-con]. Université Joseph-Fourier - Grenoble I, 2008. English. ⟨tel-00371431⟩

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