Now, researchers at the University of Illinois at Urbana-Champaign not only have discovered an unusual phenomenon in which ultra-narrow wires show enhanced superconductivity when exposed to strong magnetic fields, they also have developed a theory to explain it.
Magnetic fields are generally observed to suppress a material's ability to exhibit superconductivity – the ability of materials to carry electrical current without any resistance at low enough temperatures. Deviations from this convention have been observed, but there is no commonly accepted explanation for these exceptions, although several ideas have been proposed.
As reported in the Sept. 29 issue of Physical Review Letters, U. of I. physics professor Alexey Bezryadin (pronounced BEZ-ree-ah-dun) and his research group have studied the effect of applying a magnetic field to ultra-narrow superconducting wires only a few hundred atoms across, and have used a microscopic theory proposed by physics professor Paul Goldbart and his team to explain the results.
"My group discovered that magnetic fields can enhance the critical current in superconducting wires with very small diameters," Bezryadin said. "We spoke with many colleagues and reached the consensus that this phenomenon is indeed curious."
Magnetic fields have long been known to suppress superconductivity by raising the kinetic energy of the electrons and by influencing the electron spins. Magnetic atoms, if present in the wires, also inhibit superconductivity.
Nevertheless, as reported in the Sept. 15 issue of Europhysics Letters, Goldbart, postdoctoral researcher Tzu-Chieh Wei and graduate student David Pekker proposed that the enhancement observed by Bezyradin's group was due to magnetic moments in the wires.
"Even though the two effects – magnetic fields and magnetic moments – work separately to diminish superconductivity, together one effect weakens the other, leading to an enhancement of the superconducting properties, at least until very large fields are applied," Goldbart said.
As for the origin of these magnetic moments, the collaborating groups proposed that exposure of the wires to oxygen in the atmosphere causes magnetic moments to form on the wire surfaces. On their own, the moments weaken the superconductivity, but the magnetic field inhibits their ability to do this. This effect shows up in ultra-narrow wires because so many of their atoms lie near the surface, where the magnetic moments form.
With postdoctoral research associate Andrey Rogachev (now a physics professor at the University of Utah) and graduate student Anthony Bollinger, Bezryadin deposited either niobium or an alloy of molybdenum and germanium onto carbon nanotubes to fabricate wires that were less than 10 nanometers wide. The superconductivity of these wires under a range of applied magnetic fields was examined, and the experimental results were compared with the proposed theory, revealing an excellent correlation between the two.
"The results of this work may provide a key to explaining our previous findings that nanowires undergo an abrupt transition from superconductor to insulator as they get smaller," said Bezryadin, referring to work published in the Sept. 27 issue of Europhysics Letters.
Kristen Aramthanapon | EurekAlert!
From rocks in Colorado, evidence of a 'chaotic solar system'
23.02.2017 | University of Wisconsin-Madison
Prediction: More gas-giants will be found orbiting Sun-like stars
22.02.2017 | Carnegie Institution for Science
In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".
Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
24.02.2017 | Earth Sciences
24.02.2017 | Agricultural and Forestry Science
24.02.2017 | Life Sciences