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Scientists Discover Nano-Scale Superconducting Material

Ivan Bozovic

Researchers from the Bar-Ilan University in Israel, collaborating with the Brookhaven National Laboratory in the U.S. have designed superconducting thin films patterned with large arrays of nanowires and loops.

The temperature at which they superconduct is pretty low and hard to get for the moment – only 30 °K (-243°C). Magnetic fields have proved themselves to change the material’s electrical resistance in an unexpected manner.

“Such superconducting nanowires and nano-loops might eventually be useful for new electronic devices – that is the long-term vision,” said Brookhaven Lab physicist Ivan Bozovic, who synthesized the superconducting films. He and his collaborators describe the research in Nature Nanotechnology, published online June 13, 2010.

Conventional superconductors are limited in size, with the smallest reaching 40 nanometers (the case of niobium). If made in sizes smaller than this, they won’t act as superconductors, even if placed at the proper temperature.

The scientists at Brookhaven made superconducting thin films by using a technique called “molecular epitaxy”, and built a material with alternating layers of copper-oxide and lanthanum and strontium. They had previously used molecular epitaxy to make a single-layer copper-oxide superconducting thin film.

Then the team at Bar-Ilan used electron-beam lithography to “etch” a pattern of thousands of loops into the surface of the material. The thickness, or diameter, of the “nanowires” forming the sides of these loops was mere 25 nanometers, while the lengths ranged from 150 to 500 nanometers. Measurements of electrical resistance of the patterned arrays showed that they were indeed superconducting when cooled below about 30 K.

A fragment of a superconducting thin film patterned with nano-loops

When the scientists applied an external magnetic field perpendicular to the loops, they found that the loop resistance did not keep increasing steadily with the field strength, but rather changed up and down in an oscillatory manner.

“These oscillations in resistance have a large amplitude, and their frequency corresponds to discrete units (quanta) of magnetic flux – the measure of the strength of the magnetic field piercing the loops,” Bozovic said. “A material with such a discrete, switchable form of magneto-resistance – especially from the superconducting to the non-superconducting state – could be extremely useful for engineering new devices.”

This kind of superconducting thin films could enable small devices yield a much higher performance than they do now, without heating and losing energy, thus saving huge amounts of power. Imagine your superconductor-enabled phone lasting for several weeks or maybe a month on a single charge, with the same battery you’re using today… The only hurdle the researchers have to overcome is the low temperature used. In order to achieve higher temperature superconductivity, they will need different materials with the same properties.

Higher temperature superconductors have been built, but the size is an issue with them, when talking about nanoscale-sized devices.

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