Boson structure in the quasiparticle density of states of superconductors with nodes in the gap

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Abstract
Within a generalized Eliashberg formalism, valid for exotic pairing states of a D-wave superconductor, we have studied how details of the electron-boson spectral density responsible for superconductivity manifest themselves as structure in the quasiparticle density of states. We find that the boson structure, which is to be measured relative to the energy defined by the peak in this function, shifts very little when resonant impurity scattering is introduced. Impurity scattering, however, can fill in the density of states at zero frequency and in the region below the peak which defines a gap value. Finite-temperature effects further smear this low-frequency region, as is expected from the well-studied isotropic case. Some comments on comparison with experiments are also given.