Vortex pinning could lead to superconducting breakthroughs

February 13, 2013 by Louise Lerner
This mosaic represents the distribution of superconductivity around holes (white) in a thin sheet of superconducting film. Green indicates strong superconductivity. Further away from the holes, the superconductivity decreases (yellow, red and finally black, where the material is densely populated with vortices that interfere with superconductivity.

A team of researchers from Russia, Spain, Belgium, the U.K. and the U.S. Department of Energy's (DOE) Argonne National Laboratory announced findings last week that may represent a breakthrough in applications of superconductivity.

The team discovered a way to efficiently stabilize tiny that interfere with superconductivity—a problem that has plagued scientists trying to engineer real-world applications for decades.  The discovery could remove one of the most significant roadblocks to advances in superconductor technology.

Superconductors are extremely useful materials, given that modern society involves moving a lot of electricity around. Each time we do it, whether it be along the cord from the outlet to your lamp or in the millions of miles of power lines strung across the country, we lose a little bit of electricity. That effect is due to resistance in the wires we currently use to transport electricity. Even a pretty good , like , loses some electricity due to resistance.

But in an ideal superconductor, no electricity is ever lost. If you set up a loop of perfect and added some current, it would circle that loop forever. Superconductors are the secret behind , Maglev trains and improved cell phone reception.

The problem is that superconductors have to be cooled to do their thing. Even the "high-temperature" superconductors already discovered have to be chilled to -280° Fahrenheit. That creates a lot of engineering and logistical problems.

In the long run, scientists are hoping to develop that would operate closer to room temperature.  That would be a major achievement—though it is generally still thought to be a long way off. 

This graphic shows a strip of superconducting wire with a chain of vortices (red). The green areas show strong superconductivity. Superimposed are two curves showing the resistance of the strip depending on the magnetic field; as the magnetic field increases, the resistance first grows, then drops dramatically.

In the meantime, there remain key problems of superconductivity that need to be solved even in the low-temperature environment. 

One such major problem is posed by magnetic fields.  When magnetic fields reach a certain strength, they cause a superconductor to lose its superconductivity.  But there is a type of superconductor—known as "Type II"—which is better at surviving in relatively high magnetic fields.  In these superconductors, magnetic fields create tiny whirlpools or "vortices."  Superconducting current continues to travel around these vortices to a point, but eventually, as the strengthens, the vortices begin to move about and interfere with the material's superconductivity, introducing resistance.

"These vortices dissipate the energy when moving under applied currents and bury all hopes for a technological revolution—unless we find ways to efficiently pin them," said Argonne Distinguished Fellow Valerii Vinokur, who co-authored the study.

Scientists have spent a lot of time and effort over the past few decades trying to immobilize these vortices, but until now, the results have been mixed. They found ways to pin down the vortices, but these only worked in a restricted range of low temperatures and magnetic fields.

Vinokur and his colleagues, however, discovered a surprise. They began with very thin superconducting wires—just 50 nanometers in diameter. (A stack of 2,000 of these wires would equal the height of a sheet of paper.) These thin wires can accommodate only one row of vortices.  When they applied a high magnetic field, the vortices crowded together in long clusters and stopped moving. Increasing the magnetic field restored the material's superconductivity, instead of destroying it.

Next, the team carved superconducting film into an array of holes so that only a few vortices could squeeze between the holes, where they stayed, unable to interfere with current.

The resistance of the superconductor dropped dramatically—at temperatures and magnetic fields where no one has been able to pin vortices before. "The results were quite striking," Vinokur said.

The team has only experimented with low-temperature superconductors so far, Vinokur said, "but there is no reason why the approach we used should be restricted to just low-temperature superconductors."

The paper, "Magnetic field-induced dissipation-free state in superconducting nanostructures," is published this week in Nature Communications.

Explore further: Superconducting strip could become an ultra-low-voltage sensor

More information: www.nature.com/ncomms/journal/ … full/ncomms2437.html

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3.7 / 5 (6) Feb 13, 2013
Vinokur said, "but there is no reason why the approach we used should be restricted to just low-temperature superconductors."
Should be "but we currently know no reason"...
1 / 5 (2) Feb 15, 2013
Ultraconductors are polymer equivalents of ambient temperature superconductors.

They are useful from the region of 0Kelvin up to 200 degrees C.

See the Chava Energy website.

They are presently thin films with the conductivity normal to the film. Wire is on the horizon. Current density is presently estimated at 1 Billion amperes/cm2.

1.3 / 5 (3) Feb 16, 2013
The behavior of quantum vortices is different and way more complex, than the behavior of vortices in fluids, yet the analogies of the above experiment exists here. The motion of vortices is the source of energy dissipation in both cases. The effect of shark skin, owl wings or golf ball dimples is based on the fact, that the division of large vortices into smaller ones not only doesn't increase the fluid drag, it can even decrease it. The application of magnetic field to the niobium nanowires decreases the size of quantum vortices there, which makes their motion easier. The Latin saying "divide et impera" is based of Machiavellian approach, in which the dividing the opponents into smaller groups makes their penetration and occasional defeat smoother.

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