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arXiv · 2509.19796

Grand thermodynamic potential in a two-band unconventional superconductor

V. A. Shestakov·M. M. Korshunov
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Abstract

In a two-band system, both conventional sign-preserving $s_{++}$ and unconventional sign-changing $s_{\pm}$ 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 $\Omega$ for a two-band model with nonmagnetic impurities considered in a $\mathcal{T}$-matrix approximation. For the iron-based materials within the multiband Eliashberg theory, we show that the $s_{\pm} \to s_{++}$ transition in the vicinity of the Born limit is a first order phase transition.

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V. A. Shestakov, M. M. Korshunov. 2025-09-24. Grand thermodynamic potential in a two-band unconventional superconductor. https://arxiv.org/abs/2509.19796

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