Discuss the BCS theory

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Discuss the BCS theory

  • BCS Theory: A theory explaining the phenomenon of superconductivity devised by Bardeen, Cooper and Schrieffer, whose surnames form the name of the theory.
  • The BCS theory involves the formation of pairs of electrons in the conductivity process, which together allow the bypassing of obstacles in the crystal lattice.
  • Cooper Pairs: A loosely bound pair of electrons in a superconductor, named after Leon Cooper, who first proposed their existence.
  • The formation and effect of cooper pairs in a semiconductor takes place as follows:
    • As a negatively charged electron passes between the rows of positively charged nuclei, they are attracted towards it.
    • This distortion of the lattice causes phonons (packets of sound energy) to be emitted that form a trough of positive charges around the electron.
    • A second electron is drawn onto the trough.
    • The two electrons, which would normally repel each other, become linked by the forces exerted by the phonons.
    • The first electron has emitted a phonon and the second electron has absorbed it, thus creating an exchange of energy.
    • This exchange keeps the Cooper pair together.
    • Electron pairs are constantly forming and breaking as current is carried.
  • Newer copper-based high temperature superconductors seem to have a mixture of free electrons and Cooper pairs, and BSC theory cannot fully explain this behaviour.
  • Physicists are currently seeking to extend or modify the theory to provide an explanation.