superconductivity
DESCRIPTION
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?. - PowerPoint PPT PresentationTRANSCRIPT
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SuperconductivityBy: Shruti Sheladia, Garrett M Leavitt, Stephanie Schroeder, Christopher Dunn, Kathleen Brackney
Levitation of a magnet above a high temperature superconductor illustrating the
Meissner Effect.
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A physical state of matter that occurs at low temperatures with two key characteristics:
1. Zero Resistivity.2. Expulsion of Magnetic Flux from within the
material. (Meissner Effect)
What is Superconductivity?
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Zero Resistivity in mercury at ~1 K first observed by Dutch physicist Heike Kamerlingh Onnes in Leiden in 1911 while he was studying the properties of matter at very low temperatures.
Discovery of Superconductivity
• Onnes was awarded the Nobel Prize in Physics in 1913 for his research
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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.
Discovery & Theory of Superconductivity
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BCS Theory1. Electrons form pairs called Cooper Pairs2. Electrons move in resonance with lattice
vibrations.
Left to right: John Bardeen, Leon Cooper, J. Robert Schrieffer
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Cooper Pairs
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Critical TemperatureAt some critical temperature Tc, resistivity
abruptly drops to zero. Electrons flow freely through the lattice structure of the material.
• Resistivity of superconducting tin drops to zero at a critical temperature, whereas the normal conductor platinum does not.
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Meissner EffectWhen 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.
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Critical FieldThe 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
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Critical Field / CurrentThe 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.
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Isotope EffectLead 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.
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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)
Current Contributions
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Integrated circuits in computersWould not lose power like semiconductor based
circuits Currently the cost of superconducting computers is
too high.Higher temperature superconductors may reduce this
costMagnetic Levitation of Trains (Maglev)
Electromagnetic system; EMS (attractive maglev)Unstable equilibrium
Electrodynamics system; EDS (repulsive maglev)More stableRequires expensive superconducting magnets
Future Contributions
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Electrical generators and motorsDecrease power lossesLighter superconducting magnets could replace heavy iron
cores to create larger generators
• Superconducting transmission linesEnergy saved due to no resistive loss
Scientific researchParticle accelerators
Higher temperature magnets lower costs since liquid nitrogen costs less than liquid helium
Ceramic superconductors produce larger magnetic fields
Future Contributions cont.