The Coolest Microfridge

Physics 7, s128
A new micrometer-sized electronic cooling device features lower temperatures and higher cooling power than previously demonstrated schemes.
Hung Nguyen/Hanoi University of Science

Cutting-edge electronic cooling devices work by having hot electrons tunnel from a metal to a superconductor, carrying heat with them. A new design, which has a “drain” for removing hot particles in the superconductor, has cooled a micrometer-sized metal slab from 150 millikelvin (mK) to a record temperature of less than 30 mK. Devices based on this scheme could potentially be installed directly on a chip for cooling qubits or ultrasensitive low-temperature detectors.

The basic structure in these electronic coolers consists of two NIS (normal metal-insulator-superconductor) junctions. When voltage is applied, relatively high-energy (hot) electrons flow out of the metal and into one superconductor, while lower-energy (cooler) electrons flow in from a second superconductor. Using this technique, previous work has been able to cool a small metal piece from 100 to 40 mK. However, the scheme’s cooling potential is diminished by heat leaking back into the metal, in particular, from hot “quasiparticles” (electron-hole pairs) that reside in the superconductors.

Jukka Pekola of Aalto University School of Science, Finland, and his colleagues explored different ways to reduce heat leakage in their aluminum-based cooling devices. First, they isolated the metal from the device substrate by placing it on top of the superconductor leads. Second, they connected each superconductor to a metal (aluminum-manganese) strip, acting as a quasiparticle drain. If a hot quasiparticle enters the drain, it rapidly loses its heat to phonons in the crystal. Thanks to this heat draining, the team’s cooling devices not only go to lower temperatures but also have much higher cooling power (heat removed per time) than other designs.

–Michael Schirber

This research is published in Physical Review Applied.

Subject Areas

SuperconductivitySemiconductor PhysicsElectronicsMaterials Science

Related Articles

Allegations of Scientific Misconduct Mount as Physicist Makes His Biggest Claim Yet
Condensed Matter Physics

Allegations of Scientific Misconduct Mount as Physicist Makes His Biggest Claim Yet

Condensed-matter physicist Ranga Dias and his colleagues reported on Tuesday the discovery of a room-temperature, near-ambient-pressure superconductor; Dias is also being accused of committing scientific misconduct, including data manipulation and plagiarism. Read More »

Molecular-Orbital Electron Sources
Atomic and Molecular Physics

Molecular-Orbital Electron Sources

The molecular orbitals of a single C60 molecule on a tungsten tip can be used to shape the emission pattern of electrons. Read More »

Water is Behind the Electrification of Sand

Water is Behind the Electrification of Sand

The results of new experiments indicate that surface-adsorbed water molecules are responsible for contact electrification in granular matter, a finding that challenges established models of this phenomenon. Read More »

More Articles