Super ConductivityZero Resistance at Low

Temperatures

Contents

• History• Magnetic Properties of Superconductors• Meissner Effect• London Equations• Cooper Pairs (BCS Theory)• MagLev

History•Discovered in 1911 by H. Kamerlingh Onnes.•Discovered while investigating if resistance went to 0 Ω when T = 0K•Zero resistance occurred for Mecury at T = 4.2K• The temperature where R=0 Ω occurs is called the critical temperature.• After 60 years the highest was with = 23K•Breakthrough in 1986 with discovery of with =35K•Record at the moment held by (Tl4Ba)Ba2Ca2Cu7O13+ with a = 254K(-19C)

Conditions For Infinite Conductivity (R=0Ω)

•No P-D between two Points (Constant Potential)

•E=0 everywhere (No EMF)•B cannot change in Time

Magnetic Properties of Superconductors

• When a magnetic field is applied to a superconductor at the temperature must be lowered to maintain superconductive state.

• Every has an associated critical magnetic field .

Messnier Effect• Observed:

• Exclusion of a B field occurs, not a consequence of infinite conductivity

• Conclusive proof that superconductivity is a completely new phenomenon.

• Superconductors display perfect diamagnetism.

• Current flows only on surface.

Messnier Effect

London Conjecture

London Equations

• Cu, Ag and Au, although excellent conductors do not rank among the superconducting elements. Why?

• Answer: Only one electron in outer shell. • In Superconductive States electrons are bound

together in Cooper Pairs• This due to the electron-phonon interaction.

Cooper Pairs

BCS Theory

The BCS theory predicts a bandgap of

• Maglev (magnetic levitation) is an application of superconductivity.

• Low friction.• High Speeds• Energy efficient.

Maglev

Summary

• History• Magnetic Properties of Superconductors• Meissner Effect• London Equations• Cooper Pairs (BCS Theory)• MagLev

Type 1 and Type 2 Superconductors