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2Physics Quote:
"The exchange character of identical particles plays an important role in physics. For bosons, such an exchange leaves their quantum state the same, while a single exchange between two fermions gives a minus sign multiplying their wave function. A single exchange between two Abelian anyons gives rise to a phase factor that can be different than 1 or -1, that corresponds to bosons or fermions, respectively. More exotic exchanging character are possible, namely non-Abelian anyons. These particles have their quantum state change more dramatically, when an exchange between them takes place, to a possibly different state." -- Jin-Shi Xu, Kai Sun, Yong-Jian Han, Chuan-Feng Li, Jiannis K. Pachos, Guang-Can Guo
(Read Full Article: "Experimental Simulation of the Exchange of Majorana Zero Modes"
)

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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