K $_{1-x}$ Na $_x$ Fe $_2$ As $_2$的超导specific heat跃迁$ΔC_{\rm el} \propto T_c^β\ (β\approx 2)$
Superconducting specific heat jump $ΔC_{\rm el} \propto T_c^β\ (β\approx 2)$ for K$_{1-x}$Na$_x$Fe$_2$As$_2$
摘要：
本文系统地研究了K-$_{1-x}$-Na-$_x$-Fe-$_2$-As-$_2$超导转变温度下的电子比热跃变（$ΔC_{\rm el}$）。$T_c$和$ΔC_{\rm el}$均随着$x$的增加而单调减少。比热跃变与幂律$ΔC_{\rm el} \propto T_c^β$近似成比例，其中$β\approx 2$由杂质散射率确定，与大多数铁磷属元素化物超导体相反，其中发现了显著的Bud'ko-Ni-Canfield（BNC）标度$ΔC_{\rm el} \propto T^3$.在超导态下$C_{\rm el}(T)$的$T$依赖性和在$T_c$下$ΔC_{\rm el}$的近二次标度都被Eliashberg-两带$d$波超导体的理论与弱对破缺，由于杂质。由Na取代引起的无序显著抑制了导致轻微无序超导体中的无带隙态的小能隙，这导致在$x > 0$的超导态中观察到大的剩余索末菲系数。
英文摘要：
We present a systematic study of the electronic specific heat jump ($ΔC_{\rm el}$) at the superconducting transition temperature $T_c$ of K$_{1-x}$Na$_x$Fe$_2$As$_2$. Both $T_c$ and $ΔC_{\rm el}$ monotonously decrease with increasing $x$. The specific heat jump scales approximately with a power-law, $ΔC_{\rm el} \propto T_c^β$, with $β\approx 2$ determined by the impurity scattering rate, in contrast to most iron-pnictide superconductors, where the remarkable Bud'ko-Ni-Canfield (BNC) scaling $ΔC_{\rm el} \propto T^3$ has been found. Both the $T$ dependence of $C_{\rm el}(T)$ in the superconducting state and the nearly quadratic scaling of $ΔC_{\rm el}$ 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 $x > 0$.
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