Abstract
This paper addresses a high-performance electron-tunneling cooler based on a novel heavy-fermion/insulator/superconductor junction for millikelvin cooling applications. We show that the cooling performance of an electronic tunneling refrigerator could be significantly improved using a heavy-fermion metal to replace the normal metal in a conventional normal metal/insulator/superconductor junction. The calculation, based on typical parameters, indicates that, for a bath temperature of 300 mK, the minimum cooling temperature of an electron tunneling refrigerator is reduced from around 170 mK to below 50 mK if a heavy-fermion metal is employed in place of the normal metal. The improved cooling is attributed to an enhancement in electron tunneling due to the existence of a resonant density of states at the Fermi level.
Highlights
A normal metal/insulator/superconductor (NIS) junction exhibits a non-linear I–V characteristic when operating below the critical temperature of the superconductor
We show that the cooling performance of an electronic tunneling refrigerator could be significantly improved using a heavy-fermion metal to replace the normal metal in a conventional normal metal/insulator/ superconductor junction
The results show that the SIHIS cooler can provide up to 20 x more cooling power, depending on the peak height, and with little change in the coefficient of performance (COP) compared to the SINIS cooler
Summary
A normal metal/insulator/superconductor (NIS) junction exhibits a non-linear I–V characteristic when operating below the critical temperature of the superconductor. The superconductor band-gap prevents tunnel current at low energies and biases, but as the bias is increased, the highest energy electrons are able to tunnel out of the normal metal region. These junctions have been employed in a number of applications such as electron tunneling refrigerators for millikelvin cooling, cold electron bolometers for astronomical detectors, and point contact spectroscopy for studying Andreev reflections with heavy-fermion superconductors.
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