Lattice Dynamics and Electron–Phonon Interaction

Abstract

Studies of phonon spectra in conventional superconductors were essential in developing the microscopic theory based on the electron–phonon pairing mechanism. Phonon dispersion anomalies and peculiar temperature dependence of phonon frequencies at the superconducting phase transition have confirmed the involvement of phonons in the cooper pairing. In the theory, to calculate the superconducting Tc, both the phonon density of states (PDOS) F(ω) and the electron–phonon coupling function α²(ω) should be specified (for a review see [48, 202]). Whereas the phonon PDOS can be determined directly by inelastic neutron scattering experiments, the estimation of the electron–phonon coupling α²(ω) is a much more difficult problem. As discussed in Sect. 5.2.2, ARPES studies have revealed a substantial electron spectrum renormalization in cuprates caused by electron (hole) interaction with bosonic modes (a “kink” phenomenon) (for a review see [258]). However, it is difficult to separate the phonon and spin-fluctuation contributions in the electron spectrum renormalization. Therefore, studies of the phonon spectra of cuprate superconductors, their doping and temperature dependence, may help to elucidate the phonon role in the superconducting pairing.