Super Conductors

[Tabby]

I understand if you reduce the temperature on a conductor to absolute zero, it offers no electrical resistance because the molecules have stopped vibrating. So a current will flow indefinitely around a coil of cable. But a super conductor offers no resistance to current at a temperature above absolute zero. Why?

[jake-the-peg]

You kind of need a basic understanding of quantum mechanics to get this but basically electrons cannot normally occupy the same energy level - it's called the Pauli exclusion principle and it's why electrons occupy different "orbits" in an atom.

When the temperatore drops low enough in certain materials electrons go around in so called "Cooper pairs" this means they no longer have to obey the Pauli exclusion principle and can occupy the same energy state. The knock on from this is that they avoid collisions that cause normal resistance.

Here's a reference if you want more detail

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/bcs.html#c1

[fo3nix]

btw, absolute zero is an ideal.

termperature is just a measure of how much the atoms of the substance are vibrating: high temperature, high vibration; low temperature, low vibration. you may be familiar with the heisenbery uncertainty principle. one aspect of it is that you can never precisely know the position or momentum of something.

now, absolute zero means no temperature, and thus no vibration. this means that it has a precise point in space, and thus the uncertainty principle doesn't allow it.

so in reality, everything is shaking a little bit. in the trade we call this "quantum jitters".