BCS theory (1 Viewer)

NizDiz

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Hi peeps, just did a practice paper for this topic based on the BCS theory. I had a crack at it but ain't sure if I'm right. The question is;

The BCS theory seeks to explain superconductivity. This theory involves discussion of electron pairs. Identify two unusual properties of these electron pairs. (2 marks)

All help appreciated!! Thanks :)
 

WEMYSS

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The BCS theory seeks to explain superconductivity. This theory involves discussion of electron pairs. Identify two unusual properties of these electron pairs. (2 marks)
An unusual property of the 'electron pairs' is that they are attracted to one another despite there like charges, which is because of the positive distortion an electron leaves on a lattice when it leaves, thus attracting another electron to replace it in that position.
Another may be perhaps that these pairs can travel through the lattice without hitting any vibrating atoms (supercooled slows down vibration of crystal lattice), thus the resistance is so low, and these cooper pairs are able to form and last for an extended period of time.

My guess^
 
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Sy123

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This is a little out of syllabus, but it will help you understand BCS theory I think. What are known as electron-cooper pairs are formed because as the electrons move through the lattice, the positive charges shift slighty towards the path of the electrons since positives are attracted to it. This creates a net small positive charge in the middle of the electrons path on their way to the positive terminal.
Now, this small positive charge which is significant, attracts more and more electrons, so on the one hand the electrons are trying to stay away from each other, on the other they want to get to the mini positive charge.
If the conditions are suitable, a quantum mechanical effect happens, and the electrons form cooper pairs.

The reason why cooper pairs are useful, are because while electrons are known as thermions , cooper pairs are known as bozons. And the Pauli exclusion principle which states that no 2 thermions can occupy the same energy state. So cooper pairs are bozons and hence are not effected by Pauli Exclusion principle, which effectively allows a lot of cooper pairs to be formed and they can essentially pass through each other (someone please correct me if I'm wrong).

The reason why such a low temperature is needed to form cooper pairs, is because the amount of energy needed to form a cooper pair is 10^{-3} eV (around that), and if that energy is overcome, then the cooper pair will split.

(out of syllabus):







k is Boltzman's constant. So it can be proven that temperature needs to be around 10 Kelvin in order for cooper pairs to be formed in general.

If I explained something wrong or it is incorrect, someone please tell me.
 
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Two properties:
1. Electron pairs (Cooper pairs) travel through the lattice unimpeded. That is, with zero resistance.

2. Cooper pairs propagate through the lattice through mutual attraction. This is an unusual characteristic of particles with the same charges.
 

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