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BCS Theory is an attempt to explain superconductivity, the ability of certain materials to conduct electricity without resistance. It proposes that electrons with opposite spin can become paired, forming [Cooper pairs]?. In this process they have slightly less energy than the two electrons would have separately, and this energy gap acts like an insulating layer that stops the interactions at the electron level that lead to what we see as resistance. |
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BCS theory successfully explains low temperature superconductivity, the ability of certain materials at low temperatures to conduct electricity without resistance. BCS theory views superconductivity as a macroscopic quantum mechanical effect. It proposes that electrons with opposite spin can become paired, forming [Cooper pairs]?. An electron moving through a conductor will cause a slight increase in concentration of positive charges in the lattice around it; this increase in turn can attract another electron. In effect, the two electrons are then held together with a certain binding energy. If this binding energy is higher than the energy provided by kicks from oscillating atoms in the conductor (which is true at low temperatures), then the electron pair will stick together and resist all kicks, thus not experiencing resistance. |
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It is difficult to make an analogy, as electrons don't behave like objects we see every day. Here is one attempt: |
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BCS theory was developed in 1957 by John Bardeen, [Leon Cooper]?, and [Robert Schrieffer]?, who received the Nobel Prize for Physics in 1972 as a result. |
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Imagine you have a piece of sponge that you want to push through a pipe, but the sponge is just a little too big. Even if you get the sponge into the pipe it drags on the sides of the pipe too much to move. The sponge is an electron, and the pipe is a piece of wire. Now imagine you could add a substance (an electon) to the sponge that would make it shrink just enough to fit in the pipe, and that this substance coated the sponge with a non-stick coating (the energy gap). Now the sponge will run through the pipe with no resistance. |
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BCS theory predicts that above a temperature of 30-40 K, Cooper pair superconductivity cannot exist. In 1986, this high temperature superconductivity was however discovered, implying that at these temperatures other effects are at play; these effects are not yet fully understood. |
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BCS theory was developed by John Bardeen, [Leon Cooper]?, and [Robert Schrieffer]?, who received the Nobel Prize for Physics in 1972 as a result. |
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An excellent introduction to BCS theory and related areas of condensed matter physics at the graduate level is Schrieffer?'s book, Theory of Superconductivity, ISBN 0-7382-0120-0 (amazon.com, search). |
BCS theory was developed in 1957 by John Bardeen, [Leon Cooper]?, and [Robert Schrieffer]?, who received the Nobel Prize for Physics in 1972 as a result.
BCS theory predicts that above a temperature of 30-40 K, Cooper pair superconductivity cannot exist. In 1986, this high temperature superconductivity was however discovered, implying that at these temperatures other effects are at play; these effects are not yet fully understood.
An excellent introduction to BCS theory and related areas of condensed matter physics at the graduate level is Schrieffer?'s book, Theory of Superconductivity, ISBN 0-7382-0120-0 (amazon.com, search).
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