三斜晶系（CaFe $_{1-x}$ Pt $_x$ As）$_{10}$ Pt $_3$ As $_8$的超导性质和预形成库珀对的赝能隙
Superconducting properties and pseudogap from preformed Cooper pairs in the triclinic (CaFe$_{1-x}$Pt$_x$As)$_{10}$Pt$_3$As$_8$
摘要：
利用μ子自旋弛豫（$μ$ SR）、非弹性中子散射（INS）和核磁共振（NMR）研究了具有三斜晶系结构的新型铁基超导体（CaFe $_{1-x}$ Pt $_x$ As）$_{10}$ Pt $_3$ As $_8$（T $_{\rm c}$ = 13 K）。从$μ$ SR弛豫率测量得到的超流密度的温度依赖性表明存在两个超导能隙，$Δ_\text{1}\ggΔ_\text{2}$。根据我们的INS测量，相称的自旋波动集中在（$π$，0）波矢量，像大多数其他铁砷化物。它们的强度在T $_\text{c}$上保持不变，表明许多铁基超导体没有典型的自旋共振。相反，我们观察到的$\hslashω_0=\,$ 7毫电子伏左右的自旋激发光谱在相同的波矢，这持续高于T $_{\rm c}$和特征在于比$\hslashω_0/k_\text{B}T_\text{c}\approx\,$ 6.2，这是显着高于典型值的铁磷属元素化物的磁共振模式（~4.3）。在7毫电子伏的磁场强度的温度依赖性揭示了一个异常T* = 45 K附近的消失，这种新的模式。通过NMR观察到的自旋-晶格弛豫速率$1/T_1T$的抑制直接低于T*，在T $_{\rm c}$处没有任何明显的后续异常，表明T* 可以标记（CaFe $_{1-x}$ Pt $_x$ As）$_{10}$ Pt $_3$ As $_8$中赝能隙的开始，这可能与预先形成的库珀对的出现有关。
英文摘要：
Using a combination of muon-spin relaxation ($μ$SR), inelastic neutron scattering (INS) and nuclear magnetic resonance (NMR), we investigated the novel iron-based superconductor with a triclinic crystal structure (CaFe$_{1-x}$Pt$_x$As)$_{10}$Pt$_3$As$_8$ (T$_{\rm c}$ = 13 K), containing platinum-arsenide intermediary layers. The temperature dependence of the superfluid density obtained from the $μ$SR relaxation-rate measurements indicates the presence of two superconducting gaps, $Δ_\text{1}\ggΔ_\text{2}$. According to our INS measurements, commensurate spin fluctuations are centered at the ($π$, 0) wave vector, like in most other iron arsenides. Their intensity remains unchanged across T$_\text{c}$, indicating the absence of a spin resonance typical for many Fe-based superconductors. Instead, we observed a peak in the spin-excitation spectrum around $\hslashω_0=\,$7 meV at the same wave vector, which persists above T$_{\rm c}$ and is characterized by the ratio $\hslashω_0/k_\text{B}T_\text{c}\approx\,$6.2, which is significantly higher than typical values for the magnetic resonant modes in iron pnictides (~4.3). The temperature dependence of magnetic intensity at 7 meV revealed an anomaly around T* = 45 K related to the disappearance of this new mode. A suppression of the spin-lattice relaxation rate, $1/T_1T$, observed by NMR immediately below T* without any notable subsequent anomaly at T$_{\rm c}$, indicates that T* could mark the onset of a pseudogap in (CaFe$_{1-x}$Pt$_x$As)$_{10}$Pt$_3$As$_8$, which is likely associated with the emergence of preformed Cooper pairs.
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