A Spin Fluctuation Model for d-Wave Superconductivity

The identification of the microscopic mechanisms responsible for superconductivity and the nature of the superconducting pairing state continues to represent one of the most exciting theoretical challenges in theoretical physics[1]. In the so-called conventional superconductors, at frequencies less than or comparable to the Debye frequency, the attractive phonon-induced interaction between electrons wins out over the repulsive screened Coulomb interaction[2] and brings about superconductivity[3]. The pairing of electrons in the superconducting state is in an s-wave channel. The primacy of phonon-induced interaction in conventional superconductors has been demonstrated with great clarity. The phonon density of states, obtained by inelastic neutron scattering experiments, and the spectrum of the bosons which mediate pairing, as deduced from tunneling experiments, agree very well in systems like Pb[4,5]. In addition to the isotope effect[6,7], this comparison of two independent experiments is generally considered to be a very reliable proof of a phonon-mediated pairing state.