Iron-arsenic superconductors exhibit unique mechanism of superconductivity

April 30th, 2009 - 2:56 pm ICT by ANI  

Washington, April 30 (ANI): Physicists at the U.S. Department of Energy’s Ames Laboratory have experimentally demonstrated that the superconductivity mechanism in the recently discovered iron-arsenide superconductors is unique compared to all other known classes of superconductors.

These findings, combined with iron-arsenide’s potential good ability to carry current due to their low anisotropy, may open a door to exciting possible applications in zero-resistance power transmission.

The research, led by Ames Laboratory physicist Ruslan Prozorov, has shown that electron pairing in iron-arsenides is likely to be very different when compared to other types of known superconductors.

In superconducting materials, electrons form pairs, called Cooper pairs, below a critical temperature and these electron pairs behave identically.

The collective flow of Cooper pairs results in the most famous feature of a superconductor and the feature that draws the most interest in terms of energy efficiency: the flow of electrical current without any measurable loss of energy, or true zero resistance.

However, superconductors also have another inherent characteristic that distinguishes them from a perfect metal.

Unlike perfect metals, superconductors expel a weak magnetic field from their interiors no matter whether they are cooled in a magnetic field or whether the magnetic field is applied after cooling.

In either case, a weak magnetic field penetrates only a narrow region at a superconductor’s surface. The depth of this region is known as the London penetration depth.

“The change of the London penetration depth with temperature is directly related to the structure of the so-called superconducting gap, which in turn depends on the microscopic mechanism of how electron pairs are formed,” said Prozorov.

“London penetration depth is one of the primary experimentally measurable quantities in superconductor studies,” he added.

The variation of the London penetration depth with temperature depends on the superconducting gap structure and is already generally agreed upon in most other known classes of superconductors.

In conventional superconductors - the class made up of periodic table elements, including lead and niobium - this dependence is exponential at low temperatures.

In the high-temperature cuprate superconductors, the relationship is linear, and in magnesium-diboride superconductors, the dependence is exponential, but requires two distinct superconducting gaps to explain the data in a full temperature range.

In contrast, the Ames Laboratory research group, which includes physicists Ruslan Prozorov and Makariy Tanatar, postdoctoral researcher Catalin Martin, and graduate students, Ryan Gordon, Matt Vannette and Hyunsoo Kim, found that iron-arsenide superconductors exhibit a power-law - almost quadratic - temperature variation of penetration depth.

The Ames Lab group’s findings suggest that the iron-arsenides exhibit electron pairing different from any other known superconductor. (ANI)

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