Abstract
Electron tunneling between superconductors and normal metals has been used for an efficient refrigeration of electrons in the latter. Such cooling is a non-linear effect and usually requires a large voltage. Here we study the electron cooling in heterostructures based on superconductors with a spin-splitting field coupled to normal metals via spin-filtering barriers. The cooling power shows a linear term in the applied voltage. This improves the coefficient of performance of electron refrigeration in the normal metal by shifting its optimum cooling to lower voltage, and also allows for cooling the spin-split superconductor by reverting the sign of the voltage. We also show how tunnel coupling spin-split superconductors with regular ones allows for a highly efficient refrigeration of the latter.
Highlights
The common way to refrigerate electron systems at subKelvin temperatures is to lower the temperature of the whole sample via different refrigeration methods
Electron tunneling between superconductors and normal metals has been used for an efficient refrigeration of electrons in the latter
We study the electron cooling in heterostructures based on superconductors with a spin-splitting field coupled to normal metals via spin-filtering barriers
Summary
The common way to refrigerate electron systems at subKelvin temperatures is to lower the temperature of the whole sample via different refrigeration methods. A scheme for such direct electron refrigeration was presented more than two decades ago [1,2] It is based on electron tunneling between a superconducting (S) electrode and a normal-metal (N) island, where the gapped density of states in S allows for a selective transport of hot electrons out of N by a proper choice of the bias voltage [3]. This refrigeration method is very efficient, as the absolute temperature of the N electrons can be lowered to a tiny fraction of the starting temperature [4,5,6,7,8]. We analyze the electron refrigeration by computing the electron temperature in SS-FI-N-FI-SS, N-FI-SSFI-N and SS-FI-S -FI-SS junctions for different voltages and temperatures
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