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Superconductivity

By: Shruti Sheladia , Garrett M Leavitt, Stephanie Schroeder, Christopher Dunn , Kathleen Brackney. Superconductivity. Levitation of a magnet above a high temperature superconductor illustrating the Meissner Effect. What is Superconductivity?.

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Superconductivity

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  1. By: Shruti Sheladia,Garrett M Leavitt, Stephanie Schroeder,Christopher Dunn, Kathleen Brackney Superconductivity Levitation of a magnet above a high temperature superconductor illustrating the Meissner Effect.

  2. What is Superconductivity? • A physical state of matter that occurs at low temperatures with two key characteristics: • Zero Resistivity. • Expulsion of Magnetic Flux from within the material. (Meissner Effect)

  3. Discovery of Superconductivity • Zero Resistivity in mercury at ~1 K first observed by Dutch physicist Heike KamerlinghOnnes in Leiden in 1911 while he was studying the properties of matter at very low temperatures. • Onnes was awarded the Nobel Prize in Physics in 1913 for his research

  4. Discovery & Theory of Superconductivity • In Onnes’s original experiment, the resistivity of mercury abruptly disappeared at ~ 4.2 K • The Meissner Effect was discovered by W. Meissner and R. Ochsenfeld in 1933. • First successful theory proposed by Bardeen, Cooper, and Schrieffer in 1957.

  5. BCS Theory • Electrons form pairs called Cooper Pairs • Electrons move in resonance with lattice vibrations. Left to right: John Bardeen, Leon Cooper, J. Robert Schrieffer

  6. Cooper Pairs

  7. Critical Temperature • At some critical temperature Tc, resistivity abruptly drops to zero. Electrons flow freely through the lattice structure of the material. • Resistivity of superconductingtin drops to zero at a critical temperature, whereas the normal conductor platinum does not.

  8. Meissner Effect • When a superconductor is placed within an exterior applied magnetic field, it expels all magnetic flux from within the superconductor. • Screening currents along the surface of the superconducting material cancel the magnetic field within the material. • Magnetic flux is conserved; a larger applied field results in larger screening currents.

  9. Critical Field • The Meissner effect only works within a range. If the applied field is too large, magnetic flux does penetrate the superconductor, and superconductivity is lost. • The critical field, Bc, is temperature dependent and varies from material to material. • Bc → 0 as T → Tc

  10. Critical Field / Current • The critical field varies with temperature by: • Similarly, there is a critical current above which zero resistivity is lost, which limits the environment in which certain superconductors can be used.

  11. Isotope Effect • Lead to the successful BCS theory. • Critical temperature is dependent upon the mass of the atoms in the lattice: • Critical temperature is slightly higher for lighter isotopes.

  12. Current Contributions • The first practical application of superconductivity was developed in 1954 by Dudley Allen Buck. It was the invention of cryotron  switch - 2 superconductors with different values of magnetic fields are combined to produce a fast, simple, switch for computer elements. • Scientific Research • Superconducting magnets used to confine plasma • Large particle accelerators • Brittle ceramic magnetic coils • Medical Application • Magnetic Resonance Imaging (MRI)

  13. Future Contributions • Integrated circuits in computers • Would not lose power like semiconductor based circuits • Currently the cost of superconducting computers is too high. • Higher temperature superconductors may reduce this cost • Magnetic Levitation of Trains (Maglev) • Electromagnetic system; EMS (attractive maglev) • Unstable equilibrium • Electrodynamics system; EDS (repulsive maglev) • More stable • Requires expensive superconducting magnets

  14. Future Contributions cont. • Electrical generators and motors • Decrease power losses • Lighter superconducting magnets could replace heavy iron cores to create larger generators • Superconducting transmission lines • Energy saved due to no resistive loss • Scientific research • Particle accelerators • Higher temperature magnets lower costs since liquid nitrogen costs less than liquid helium • Ceramic superconductors produce larger magnetic fields

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