Superconductivity

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Stickstoff gekühlter Supraleiter schwebt über Dauermagneten 2009-06-21

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Periodic table with superconducting temperatures

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Cross section of preform superconductor cable

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File:Meissner effect.ogv Superconductivity is a physical phenomenon characterized by the complete absence of electrical resistance in certain materials when they are cooled below a characteristic critical temperature. This phenomenon was first discovered in 1911 by Heike Kamerlingh Onnes, who observed it in mercury at a temperature of approximately 4.2 Kelvin. Superconductivity is a quantum mechanical phenomenon that allows for the electrons in a superconductor to move without energy loss, which has significant implications for electrical systems and magnetic fields.

Discovery and History

The discovery of superconductivity has its roots in the exploration of the properties of materials at low temperatures. The quest to understand the behavior of conductors at the brink of absolute zero led to the groundbreaking discovery by Onnes, which opened up a new field of research in condensed matter physics. Since then, various materials have been found to exhibit superconductivity at different critical temperatures. The development of alloys and ceramic materials, known as high-temperature superconductors, has extended the critical temperature closer to practical and economically viable levels.

Mechanism

The theoretical understanding of superconductivity was significantly advanced in 1957 with the proposal of the BCS theory by John Bardeen, Leon Cooper, and Robert Schrieffer. This theory explains superconductivity as a result of Cooper pairs of electrons moving through a crystal lattice without scattering, due to a phonon-mediated attraction between electrons. The formation of these Cooper pairs leads to a state where the material can conduct electricity without resistance. The BCS theory, however, primarily applies to conventional superconductors, typically those with lower critical temperatures.

For high-temperature superconductors, the mechanism behind superconductivity is still an area of active research, with various theories suggesting the involvement of more complex interactions.

Applications

Superconductivity has a wide range of applications due to its unique properties. In the field of magnet technology, superconductors are used to create powerful magnets for magnetic resonance imaging (MRI) machines, particle accelerators, and magnetic levitation (maglev) trains. The zero resistance property is also exploited in superconducting quantum interference devices (SQUIDs), which are highly sensitive magnetometers used in various scientific and medical applications.

In the area of power transmission, superconducting materials offer the potential for lossless electricity transmission over long distances, although practical and economic challenges remain. Additionally, superconductors are being explored for their potential in quantum computing, where their ability to maintain quantum coherence over longer periods can be highly advantageous.

Challenges and Future Directions

Despite the promising applications of superconductivity, there are significant challenges to its widespread adoption. The requirement for cooling materials to extremely low temperatures is a major hurdle, especially for high-temperature superconductors, which still require cooling well below room temperature. Research is ongoing to discover new materials that exhibit superconductivity at higher temperatures, potentially even at room temperature, which would revolutionize many fields by making superconducting technologies more accessible and cost-effective.

See Also

• Electrical conductivity
• Quantum mechanics
• Cryogenics
• Superfluidity