Last lectures: Superconductivity I - Experimental Facts
Discovered in 1911 in Hg - 4.6 K - R apparently drops to ZERO suddenly
Which materials? NOT magnetic material like Fe,
NOT the "best" metals like Cu
Exclusion of magnetic fields
Meisner Effect shows a superconductor is not just a perfect conductor
NEW PHASE OF MATTER
Heat Capacity shows there is a phase transition
Below Tc< there is a gap -like an insulator!
Transition is reversible - no hysteresis
Isotope effect - something to do with MOTION of nuclei
Type I and Type II
Today: Superconductivity - Concepts and Theory
Exclusion of magnetic fields can be used to derive energy of the
superconducting state
Shows very small energy Delta F ~ D(EFermi) Delta E2 ~ Delta k2
where the gap is consistent with heat capacity
How does a superconductor exclude B field?
London penetration depth (1930’s)
Superconductor forms a quantum state
Flux Quantization
How we know currents are persistent!
Cooper instability - electron pairs
Instability of Fermi surface if there is attractive interaction
Bardeen, Cooper, Schrieffer theory (1957)
Phonons can provide attractive interaction - "Mattress Effect"
BCS had the idea for how to form the new quantum state where
all the electrons together form a single bound state seperated by a gap from
all other states
NEW STATE OF MATTER!
Nobel Prize for work done in Loomis Lab
BCS theory explians all the phenomena and gives expression for
the gap and the transition temperature