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The Nature of the Cooper Pair - University of Liverpool

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<strong>The</strong> potential energy <strong>of</strong> an electron due to a positive ion is<br />

U = − e2<br />

4πɛ0r .<br />

This is normally cancelled out by <strong>the</strong> free electrons. If an ion is<br />

displaced, <strong>the</strong> change in <strong>the</strong> potential is <strong>the</strong> attractive potential<br />

that now appears. This may be estimated by <strong>the</strong> small change<br />

approximation:<br />

δU ≈ dU<br />

dr δr.<br />

Superconductivity 3

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