BCS Theory

A qualitative explanation of superconductivity was given by three scientists.
The theory is recognized as BCS Theory (B Bardeen, C Cooper, S Schrieffer).

BCS theory showed that the basic interaction responsible behind superconductivity. It may appear to be that of a pair of electrons by means of an interchange of virtual phonon.

Suppose an electron having energy E approaches a positive ion core. It will suffer an attractive Coulomb interaction. It will lose its energy to the iron core. Let the amount of loosed energy b K. The amount of energy left with the electron will b equal to (E-K ). This attraction the iron core undergoes motion and distorts the crystal lattice.

Another electron has energy E come in the way of the distorted lattice. The resulting interaction between them will lead to a transfer of energy (K) from the core to the electron.

Now, this election will have an energy equal to (E+K). There is an exchange of virtual energy (called phonon). Between two electrons through the ion Crystal. The two electrons interact indirectly. Through lattice distortion and lowering the energy of the electron.

This type of interaction is called electron interaction through photons. Two electrons are called Cooper pair.

Cooper pair is a pair of two electrons having opposite spin. This is associated with lattice deformation and formed by electron-phonon interaction.

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