This theory was developed by Bardeen, Cooper and Schrieffer in 1957based on electron- lattice- electron interaction. According to thistheory, an electron attracts lattice ions towards itself, so that it
is surrounded by a region of positive charges. Another gets attractedto this region of high positive ion concentration. Thus an electron-lattice- electron interaction results in an electron pair formation.These pairs are called Cooper pairs. They can be scattered only if theenergy involved is sufficient to break it up into two singleelectrons.Cooper pair electrons possess opposite momenta and spin (K and –K).In addition, a Cooper pair does not obey Pauli's exclusion principleand hence any number of Cooper pairs can be accommodated into a singlequantum state.Since an electron pair has a lower energy than the two normalelectrons, there is an energy gap between the paired (Cooper pair) andthe two single electrons.As long as Cooper pair electrons remain in Cooper pair states, they donot suffer scattering and hence resistivity will be zero. When thetemperature is raised, to overcome the energy gap, Cooper pairelectrons gets separated to normal single electrons which may undergoscattering due to the presence of imperfections in the crystal orlattice vibrations, which leads to a finite resistivity.
is surrounded by a region of positive charges. Another gets attractedto this region of high positive ion concentration. Thus an electron-lattice- electron interaction results in an electron pair formation.These pairs are called Cooper pairs. They can be scattered only if theenergy involved is sufficient to break it up into two singleelectrons.Cooper pair electrons possess opposite momenta and spin (K and –K).In addition, a Cooper pair does not obey Pauli's exclusion principleand hence any number of Cooper pairs can be accommodated into a singlequantum state.Since an electron pair has a lower energy than the two normalelectrons, there is an energy gap between the paired (Cooper pair) andthe two single electrons.As long as Cooper pair electrons remain in Cooper pair states, they donot suffer scattering and hence resistivity will be zero. When thetemperature is raised, to overcome the energy gap, Cooper pairelectrons gets separated to normal single electrons which may undergoscattering due to the presence of imperfections in the crystal orlattice vibrations, which leads to a finite resistivity.
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