How cooper pairs formed?
if we decrease the temperature of a semiconductor, it will become superconductor. ok, its resistance decrases to zero. as we decrease the temperature the motion of electron ceases, so it become static, now after that what happen, explain me.
- Cooper Pairs00
- Although Cooper pairing is a quantum effect, the reason for the pairing can be seen from a simplified classical explanation. An electron in a metal normally behaves as a free particle. The electron is repelled from other electrons due to their negative charge, but it also attracts the positive ions that make up the rigid lattice of the metal. This attraction distorts the ion lattice, moving the ions slightly toward the electron, increasing the positive charge density of the lattice in the vicinity. This positive charge can attract other electrons. At long distances this attraction between electrons due to the displaced ions can overcome the electrons' repulsion due to their negative charge, and cause them to pair-up. The rigorous quantum mechanical explanation shows that the effect is due to electron–phonon interactions.
The energy of the pairing interaction is quite weak, of the order of 10−3eV, and thermal energy can easily break the pairs up. So only at low temperatures are a significant number of the electrons in a metal in Cooper pairs. The electrons in a pair are not necessarily close together; because the interaction is long range, paired electrons may still be many hundreds of nanometers apart. This distance is usually greater than the average interelectron distance, so many Cooper pairs can occupy the same space. Electrons have spin-1⁄2, so they are fermions, but a Cooper pair is a composite boson as its total spin is integer (0 or 1). This means the wave functions are symmetric under particle interchange, and they are allowed to be in the same state. The tendency for all the Cooper pairs in a body to 'condense' into the same ground quantum state is responsible for the peculiar properties of superconductivity. In this condensed quasi-boson state, the electrons are no longer subject to the usual forces that cause resistance when they are behaving as fermions.00
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