BCS theory

BCS theory successfully explains conventional superconductivity, the ability of certain metals 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.

More details

BCS theory starts from the assumption that there is some attraction between electrons, which can overcome the Coulomb repulsion. In most materials (in low temperature superconductors), this attraction is brought about indirectly by the coupling of electrons to the crystal lattice (as explained above). However, the results of BCS theory do not depend on the origin of the attractive interaction. Note that the original results of BCS (discussed below)

Related Topics:
Coulomb repulsion - Crystal lattice

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were describing an "s-wave" superconducting state, which is the rule among low-temperature superconductors but is not realized in many "unconventional superconductors", such as the "d-wave" high-temperature superconductors.

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Extensions of BCS theory exist to describe these other cases, although they are insufficient to completely describe the observed features of high-temperature superconductivity.

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BCS were able to give an approximation for the quantum-mechanical state of the

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system of (attractively interacting) electrons inside the metal. This state is

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now known as the "BCS state". Whereas in the normal metal electrons move independently, in the BCS state they are bound into "Cooper pairs" by the attractive interaction.

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BCS have derived several important theoretical predictions that are independent

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of the details of the interaction (note that the quantitative predictions mentioned below hold only for sufficiently weak attraction between the electrons, which is however fulfilled for many low temperature superconductors

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