Manifestation of impurity induced s_{+-} -> s_{++} transition: multiband   model for dynamical response functions
  We investigate 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 like ARPES, tunneling and terahertz spectroscopy may be used for revealing of information about the underlying order parameter symmetry. 
D.V. Efremov, A.A. Golubov and O.V. Dolgov
cond-mat.supr-con