Cooper pair

A Cooper pair is a correlated pair of electrons that behaves collectively as a boson. In conventional superconductors, an effective attraction binds the electrons into pairs that enable resistance-free current.

Electron-phonon interaction: The coupling between electrons and quantized lattice vibrations called phonons. In conventional superconductors, phonons mediate the attraction that binds Cooper pairs.
Pauli exclusion principle: The rule that identical fermions cannot occupy the same quantum state. It constrains the allowed spin and orbital states of two paired electrons.
Leon Cooper: An American physicist who showed that an arbitrarily weak attraction can bind electrons above a filled Fermi sea. His 1956 result established the instability that gives Cooper pairs their name.
Superconducting quantum interference device: A superconducting loop containing Josephson junctions, used to detect extremely small magnetic fields. Its interference signal depends on coherent superconducting pair currents.
Bose–Einstein condensation of molecules: A condensate formed from tightly bound bosonic molecules at low temperature. It contrasts with conventional superconductors, where Cooper pairs are usually large and overlap extensively.
Fermi surface: The boundary in momentum space between occupied and unoccupied electron states at zero temperature. Pairing is especially effective for electrons near this boundary.
Fermion: A particle with half-integer spin that obeys Fermi–Dirac statistics. Each electron is a fermion, while a Cooper pair has integer total spin.
Cooper problem: The two-electron problem of finding a bound state above a filled Fermi sea under weak attraction. It isolates the first mathematical demonstration of pair formation.
Superconducting qubit: A quantum-information device built from superconducting circuits with discrete energy levels. Its circuit dynamics rely on collective superconducting degrees of freedom formed by paired electrons.
Unconventional superconductor: A superconductor whose pairing cannot be explained by conventional phonon-mediated BCS theory. Its pairing symmetry or mechanism may differ from that of conventional Cooper pairs.

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