%0 Journal Article
%T Superconducting specific heat jump $¦¤C_{\rm el} \propto T_c^¦Â \ (¦Â\approx 2)$ for K$_{1-x}$Na$_x$Fe$_2$As$_2$
%A V. Grinenko
%A D. V. Efremov
%A S. -L. Drechsler
%A S. Aswartham
%A D. Gruner
%A M. Roslova
%A I. Morozov
%A K. Nenkov
%A S. Wurmehl
%A A. U. B. Wolter
%A B. Holzapfel
%A B¨¹chner
%J Physics
%D 2013
%I arXiv
%R 10.1103/PhysRevB.89.060504
%X We present a systematic study of the electronic specific heat jump ($\Delta C_{\rm el}$) at the superconducting transition temperature $T_c$ of K$_{1-x}$Na$_x$Fe$_2$As$_2$. Both $T_c$ and $\Delta C_{\rm el}$ monotonously decrease with increasing $x$. The specific heat jump scales approximately with a power-law, $\Delta C_{\rm el} \propto T_c^{\beta}$, with $\beta \approx 2$ determined by the impurity scattering rate, in contrast to most iron-pnictide superconductors, where the remarkable Bud'ko-Ni-Canfield (BNC) scaling $\Delta C_{\rm el} \propto T^3$ has been found. Both the $T$ dependence of $C_{\rm el}(T)$ in the superconducting state and the nearly quadratic scaling of $\Delta C_{\rm el}$ at $T_c$ are well described by the Eliashberg-theory for a two-band $d$-wave superconductor with weak pair-breaking due to nonmagnetic impurities. The disorder induced by the Na substitution significantly suppresses the small gaps leading to gapless states in the slightly disordered superconductor, which results in a large observed residual Sommerfeld coefficient in the superconducting state for $x > 0$.
%U http://arxiv.org/abs/1308.2201v2