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Electron-Phonon Interactions and Superconductivity

One of Frohlich’s major achievements was to point out [1], in 1950, the significance of the electron-phonon interaction in superconductivity. Earlier, interactions between electrons and phonons (the quanta of the lattice vibrations) were taken into account for scattering and resistance; FRoHLICH showed that the same interaction should modify the energy of the electrons and proposed it as the basis for a theory of superconductivity. He suggested using a Hamiltonian, now called the Frohlich Hamiltonian, in which Coulomb interactions are disregarded except as they may modify the energies of the individual electrons, but which includes the interaction between electrons and phonons. An effective attractive interaction between the electrons results from exchange of virtual phonons. Strong confirmation of the importance of electron-phonon interactions in superconductivity came from the independent experimental discovery of the isotope effect. Although the theory given at that time was unsuccessful in accounting for superconductivity, FRoHLICH’S formulation of the problem has been the basis for nearly all subsequent theoretical developments.