Researchers build SQUID device that demonstrates the Josephson effect

(Phys.org)—Italian nano-science researchers Francesco Giazotto and María José Martínez-Pérez have built a superconducting quantum interference device (SQUID) that confirms a theory that describes the Josephson effect, whereby the application of a magnetic field applied to such a device can cause changes in the amount of heat that flows through it. They describe their device and how it works in a paper they've published in the journal Nature.

Half a century ago, physicist Brian Josephson predicted that a device now known as a Josephson junction could be built. Such a device would consist of two superconductors connected together with a small amount of insulating material between them. Josephson said because of the unique properties of such a device, electrons should be able move from one of the superconductors to the other by "tunneling" through the insulator. Subsequent research proved this to be correct, and devices that incorporate it have been created to measure very small magnetic fields.

But theory also suggested that if a magnetic field were applied to the device, the amount of heat that moved between the two superconductors could be impacted. Until now, this had not been demonstrated with a real device. To create one, the researchers fashioned two Y shaped pieces of a superconductor then connected them together at their tops, with a small amount of insulating material between them. In this setup the conjoined materials formed a loop.

To test the heat transfer properties, the researchers heated one side of the loop and cooled the other, then measured the amount of heat transfer between the two as variable strength magnetic fields were applied. They found that varying the strength of the magnetic field did indeed cause more or less heat to move from one side of the SQUID to the other. They even found that in some cases, heat could be caused to move from the cold side to the hot.

The researchers explain that varying the magnetic field can cause changes in heat flow because of the quantum phase difference between the two superconductors. Changes in the strength of the magnetic field can cause peaks in the wavefunctions of the two superconductors to line up, thereby increasing heat flow, or force the reverse, resulting in decreased heat flow.

These new findings, the researchers say might help in developing better magnetometers, or perhaps even lead the way to computing devices based on thermal transistors.