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[Phys-L] superconductivity

I am trying to understand (Type I) superconductivity. Here is what I understand so far:

A periodic potential exists in a perfectly crystalline conducting solid such that electrons can travel without resistance unless they encounter
a) impurities (in which case it is not a perfect crystal)
b) vibrations in the crystal lattice, known as phonons. When the electrons encounter these things they scatter which shows up macroscopically as resistance. In a truly perfect crystal at 0K we should expect to find 0 resistance. (Thanks to a document due to Carl Mungan I found on the web for details on this.)

Some interesting substances display this property (and others) at T>0K. They are called superconductors. The mechanism which allows this to occur is coupling of electrons due to phonons, effectively combining two fermions into a boson and lowering the overall energy of the electrons. Somehow (this is where I am fuzzy) this prevents the electron pairs to avoid being scattered by phonons or impurities.

How correct is the above and what are the missing details at the end? I have looked in some solid state books and googled to no avail.

Justin Parke
Oakland Mills High School
Columbia, MD
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