Manifestations of impurity-induced s±⇒s++ transition: Multiband model for dynamical response functions

We investigate the effects of disorder on the density of states, the single-particle response function and optical conductivity in multiband superconductors with s± symmetry of the order parameter, where s± → s++ transition may take place. In the vicinity of the transition, the superconductive gapless regime is realized. It manifests itself in anomalies in the above-mentioned properties. As a result, intrinsically phase-insensitive experimental methods such as angle-resolved photoemission spectroscopy, tunneling and terahertz spectroscopy may be used to reveal information about the underlying order parameter symmetry