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arXiv 0902.1020cond-mat.supr-con
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铁基超导体$\pm$ s波态的超流密度

Superfluid density of the $\pm$s-wave state for the iron-based superconductors

Yunkyu Bang

摘要:

研究了铁基超导体最小两带模型的$\pm$ s波态的超流密度及其随杂质浓度的演化。我们表明,强耦合极限的杂质散射诱导的自能的一般形式$Im Σ_{imp} (ω) \approx i γ+ i βω$超过一个临界杂质浓度$Γ_{imp} > Γ_{crit}$。这种形式的$Im Σ_{imp} (ω)$导致超流密度$[ρ_{s}(T) - ρ_{s}(0)] \approx - γT^2 -βT^3$的温度依赖性。结合较低杂质浓度$Γ_{imp} < Γ_{crit}$的$ρ_{s}(T)$的全隙行为,$\pm$ s波状态产生$Δλ(T)$的连续演化:随着杂质浓度的增加,指数平坦的$\to T^3 \to T^2$与Fe磷属元素化物超导体如$M$-1111的测量一致($M$ =La,Nd,Sm,Pr)和Ba-122,除LaFePO外,最近的实验表明其在低温下显示出$Δλ(T) \propto T^{1.2}$。我们的研究结果还表明,态密度(DOS)测量的热力学性质和DOS测量的输运性质一般可以是不同的。

英文摘要:

We study the superfluid density of the $\pm$s-wave state of the minimal two band model for the Fe-based superconductors and its evolution with impurity concentration. We show that the impurity scattering of the strong coupling limit induces the selfenergy of a generic form $Im Σ_{imp} (ω) \approx i γ+ i βω$ beyond a critical impurity concentration $Γ_{imp} > Γ_{crit}$. This form of $Im Σ_{imp} (ω)$ causes the temperature dependence of the superfluid density $[ρ_{s}(T) - ρ_{s}(0)] \approx - γT^2 -βT^3$. Combining with the full gap behavior of $ρ_{s}(T)$ for lower impurity concentration $Γ_{imp} < Γ_{crit}$, the $\pm$s-wave state produces a continuous evolution of $Δλ(T)$: exponentially flat $\to T^3 \to T^2$ with increasing impurity concentration that is consistent with the measurements of the Fe pnictide superconductors such as $M$-1111 ($M$=La,Nd,Sm,Pr) and Ba-122 with various dopings, except LaFePO which shows $Δλ(T) \propto T^{1.2}$ at low temperatures by recent experiment. Our results also demonstrate that the density of states (DOS) measured by thermodynamic properties and the DOS measured by transport properties can in general be different.

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