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Topic outline

 

  • Time: 12 hours
    Level: Advanced

 
 

Introduction

  • Introduction Resource
  • The fascinating phenomenon of superconductivity and its potential applications have attracted the attention of scientists, engineers and businessmen. Intense research has taken place to discover new superconductors,...
 

1 Superconductivity

  • 1 Superconductivity Resource
  • Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes (Figure 1) as he studied the properties of metals at low temperatures. A few years earlier he had become the first person to liquefy helium,...
 

2 Properties of superconductors

  • 2.1 Zero electrical resistance Resource
  • In this section we shall discuss some of the most important electrical properties of superconductors, with discussion of magnetic properties to follow in the next section.
  • 2.2 Persistent currents lead to constant magnetic flux Resource
  • An important consequence of the persistent currents that flow in materials with zero resistance is that the magnetic flux that passes through a continuous loop of such a material remains constant. To see...
  • 2.3 The Meissner effect Resource
  • The second defining characteristic of a superconducting material is much less obvious than its zero electrical resistance. It was over 20 years after the discovery of superconductivity that Meissner and...
  • 2.4 Critical magnetic field Resource
  • An important characteristic of a superconductor is that its normal resistance is restored if a sufficiently large magnetic field is applied. The nature of this transition to the normal state depends on...
  • 2.5 Critical current Resource
  • The current density for a steady current flowing along a wire in its normal state is essentially uniform over its cross-section. A consequence of this is that the magnetic field strength B within a wire...
 

3 Modelling properties of superconductors

  • 3.1 A two-fluid model Resource
  • As was mentioned earlier, a substantial dose of quantum mechanics would be required to provide a full explanation of the properties of superconductors. This would take us too far away from electromagnetism,...
  • 3.2 Magnetic field in a perfect conductor Resource
  • When discussing the Meissner effect in Subsection 2.3, we argued qualitatively that a material that just had the property of zero resistance – a perfect conductor rather than a superconductor – would maintain...
  • 3.3 The London equations Resource
  • A simple but useful description of the electrodynamics of superconductivity was put forward by the brothers Fritz and Heinz London in 1935, shortly after the discovery that magnetic fields are expelled...
  • 3.4 Penetration depth Resource
  • The characteristic length, λ, associated with the decay of the magnetic field at the surface of a superconductor is known as the penetration depth, and it depends on the number density ns of superconducting...
  • 3.5 The screening current Resource
  • The London equations relate the magnetic field in a superconductor to the superconducting current density, and we derived the dependence of field on position by eliminating the current density. However,...
 

4 Two types of superconductor

  • Preamble Resource
  • The two main types of superconducting materials are known as type-I and type-II superconductors, and their properties will be discussed in the remainder of this unit. All of the pure elemental superconductors...
  • 4.1 Type-I superconductors Resource
  • You saw in Subsection 2.4 that superconductivity in a tin cylinder is destroyed when an applied field with strength B0  > Bc is applied parallel to the cylinder. However, when the field is applied perpendicular...
  • 4.2 Type-II superconductors Resource
  • For decades it was assumed that all superconductors, elements and alloys, behaved in similar ways, and that any differences could be attributed to impurities or defects in the materials. However, in 1957,...
 

5 Summary

  • 5 Summary Resource
  • Section 1 Superconductivity was discovered in 1911, and in the century since then there have been many developments in knowledge of the properties of superconductors and the materials that become superconducting,...
 

References and Acknowledgements

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