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Limitations in cooling electrons by normal metal - superconductor tunnel junctions

J. P. Pekola·T. T. Heikkila·A. M. Savin·J. T. Flyktman·F. Giazotto·F. W. J. Hekking
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Abstract

We demonstrate both theoretically and experimentally two limiting factors in cooling electrons using biased tunnel junctions to extract heat from a normal metal into a superconductor. Firstly, when the injection rate of electrons exceeds the internal relaxation rate in the metal to be cooled, the electrons do no more obey the Fermi-Dirac distribution, and the concept of temperature cannot be applied as such. Secondly, at low bath temperatures, states within the gap induce anomalous heating and yield a theoretical limit of the achievable minimum temperature.

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J. P. Pekola, T. T. Heikkila, A. M. Savin, J. T. Flyktman, F. Giazotto, F. W. J. Hekking. 2004-02-09. Limitations in cooling electrons by normal metal - superconductor tunnel junctions. https://doi.org/10.1103/physrevlett.92.056804

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