2025/09/24 by Shestakov, V. A., Korshunov, M. M.
#FOS: Physical sciences #Superconductivity (cond-mat.supr-con)
paper · doi:10.48550/arxiv.2509.19796
In a two-band system, both conventional sign-preserving s++ and unconventional sign-changing s± superconducting state may appear at low temperatures. Moreover, they may transform from one to another due to the impurity scattering. To study the details of such a transition here we derive the expression for the Grand thermodynamic potential Ω for a two-band model with nonmagnetic impurities considered in a T-matrix approximation. For the iron-based materials within the multiband Eliashberg theory, we show that the s± → s++ transition in the vicinity of the Born limit is a first order phase transition.