We show that a localized bosonic mode acts as a new type of "defect" in s- and d_{x^2-y^2}-wave superconductors. The mode induces bound or resonance states, whose spectral signature are peaks in the superconductor's density of states (DOS). We study the peaks' shape and energy as a function of temperature and the mode's frequency and lifetime. We identify several characteristic signatures of the localized mode that qualitatively distinguishes its effects from those of magnetic or non-magnetic impurities.
@article{arxiv.cond-mat/0304169,
title = {Localized Bosonic Modes in Superconductors},
author = {Dirk K. Morr and Roy H. Nyberg},
journal= {arXiv preprint arXiv:cond-mat/0304169},
year = {2009}
}