Pairs of Cooper Pairs...


New state of matter: The team observed electron quadruplets in this iron-based superconductor material, seen mounted for experimental measurements. (Courtesy: Vadim Grinenko, Federico Caglieris)

Topics: Condensed Matter Physics, Solid-State Physics, Superconductors

Note: I gave my research proposal last Friday. I have been answering some concerns about my proposal for the committee. I followed the outline sent to me by my advisor. I hope I've answered them sufficiently. I will post today and tomorrow; next week on Monday, Wednesday, and Friday. I tutor Calculus. For a person finished with classes, I'm extremely busy.

Cool a material below its superconducting transition temperature and you’d expect it to start conducting electricity without resistance and expelling magnetic fields. But an international group of physicists has found that a certain kind of iron-based material doped with negative charges does the opposite at around the same temperature – producing spontaneous magnetic fields and retaining resistance when chilled. The researchers say that the results point to a new state of matter in which electrons flow in correlated groups of four, rather than two.

According to the Bardeen-Cooper-Schrieffer (BCS) theory, superconductivity occurs when electrons get together to form what is known as Cooper pairs. Whereas in a vacuum two electrons would repel each other, when moving through the crystal lattice of a superconducting material, one of these particles shifts the positions of surrounding atoms to leave a small region of positive charge. This attracts the second electron to create the pair.

The creation of many such pairs yields a collective condensate, which results in frictionless electron flow. This occurs below a certain temperature – the superconducting transition temperature (Tc) – at which point atoms lack the thermal energy to break up the pairs.

Superconductor reveals new state of matter involving pairs of Cooper pairs, Edwin Cartlidge, Physics World

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