Decisive proofs of the $s_{\pm }\to s_{++}$ transition in the temperature dependence of the magnetic penetration depth

Abstract

One of the features of the unconventional $s_{\pm }$ state in iron-based superconductors is possibility to transform to the $s_{++}$ state with the increase of the nonmagnetic disorder. Detection of such a transition would prove the existence of the $s_{\pm }$ state. Here we study the temperature dependence of the London magnetic penetration depth within the two-band model for the $s_{\pm }$ and $s_{++}$ superconductors. By solving Eliashberg equations accounting for the spin-fluctuation mediated pairing and nonmagnetic impurities in the $T$-matrix approximation, we have derived a set of specific signatures of the $s_{\pm }\to s_{++}$ transition: (1) sharp change in the behavior of the penetration depth ${\lambda }_L$ as a function of the impurity scattering rate at low temperatures; (2) before the transition, the slope of $\Delta {\lambda }_L(T)={\lambda }_L(T)-{\lambda }_L(0)$ increases as a function of temperature, and after the transition this value decreases; (3) the sharp jump in the inverse square of the penetration depth as a function of the impurity scattering rate, ${\lambda }_L^{-2}({\Gamma }_a)$, at the transition; (4) change from the single-gap behavior in the vicinity of the transition to the two-gap behavior upon increase of the impurity scattering rate in the superfluid density ${\rho }_s(T)$.

8 pages, 6 figures

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Cited by in corpus (2)

• Thermodynamics of $s_{\pm }-to-s_{++}$ transition in iron pnictides in the vicinity of the Born limit
• Critical point of the transition between $s_{\pm }$ and $s_{++}$ states of a two-band superconductor with nonmagnetic impurities