The sharp forward electron-phonon (FEP) and impurity (FIS) scattering change the normal and superconducting properties significantly. The pseudo-gap like features are present in the density of states for ω<Ω, where Ω is the phonon frequency. The superconducting critical temperature Tc, due to the FEP pairing, is linear with respect to the electron-phonon coupling constant. The FIS impurities are pair weakening for s− and d−wave pairing.
@article{arxiv.cond-mat/9804081,
title = {Forward Electron-Phonon Scattering in Normal and Superconducting States},
author = {O. V. Dolgov and O. V. Danylenko and M. L. Kulic and V. Oudovenko},
journal= {arXiv preprint arXiv:cond-mat/9804081},
year = {2015}
}