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2Physics Quote:
"Lasers are light sources with well-defined and well-manageable properties, making them an ideal tool for scientific research. Nevertheless, at some points the inherent (quasi-) monochromaticity of lasers is a drawback. Using a convenient converting phosphor can produce a broad spectrum but also results in a loss of the desired laser properties, in particular the high degree of directionality. To generate true white light while retaining this directionality, one can resort to nonlinear effects like soliton formation."
-- Nils W. Rosemann, Jens P. Eu├čner, Andreas Beyer, Stephan W. Koch, Kerstin Volz, Stefanie Dehnen, Sangam Chatterjee
(Read Full Article: "Nonlinear Medium for Efficient Steady-State Directional White-Light Generation"
)

Tuesday, May 16, 2006

Superconductivity Theory Proven

Chandra Varma (Photo courtsey: UC-Riverside)

A French-German team of experimental scientists has announced that they could verify the central prediction of a high-temperature superconductivity theory proposed by a Prof Chandra Varma, currently a physics professor at the University of California-Riverside.

Superconductors are materials that conduct electricity with near-zero resistance below a specific temperature, known as the critical temperature. Superconductors typically find use in electric power transformers and magnetic resonance imaging machines. Conventional metallic superconductors must be cooled below -424 F to become superconducting.

The scientists say this verification might assist in the fabrication of materials that are superconducting at room temperature. And it will help settle a contentious, international debate on the fundamental physics of superconductivity and emergent states of matter.

Varma's initial theory, proposed in 1989 while he was working for IBM, stated the radical idea that high-temperature superconductivity and related phenomena occur in certain materials because quantum-mechanical fluctuations in those materials increase as temperature decreases. Usually such fluctuations -- determining the properties of all matter in the universe -- decrease as temperature decreases.

In 1996 Prof. Varma noted that in copper oxide materials superconductivity is associated with the formation of a new state of matter in which electric current loops form spontaneously, going from copper to oxygen atoms and back to copper. The French-Italian group directly observed the current loops in experiments involving the diffraction of polarized neutrons. In these experiments a beam of neutrons changes direction as well as the direction of its magnetization in a manner that is closely related to the geometrical arrangement of the current loops inside the material in which the beam is made to pass.

Results of this experimental verification is detailed in the May 19 issue of Physical Review Letters. Here's the abstract.

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