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
Top Related