Bipolarons and superconductivity

The problem of deformation induced attraction leading to localized pairs of electrons, the so-called bipolarons, is studied in detail. The analogy between bipolarons and itinerant Cooper pairs in a superconductor is explored. It is shown that the two types of pairing result from the microscopic nature of the electron-phonon Hamiltonian and that following the coupling constant the ground-state becomes a bipolaronic insulator beyond a critical coupling strength. A phase diagramme between a metal, superconductor and bipolaronic insulator is proposed.

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