质子辐照超导Ca $_{0.5}$ Na $_{0.5}$ Fe $_2$ As $_2$单晶抑制超流密度的磁穿透深度测量
Magnetic penetration-depth measurements of a suppressed superfluid density of superconducting Ca$_{0.5}$Na$_{0.5}$Fe$_2$As$_2$ single crystals by proton irradiation
Jeehoon Kim, N. Haberkorn, M. J. Graf, I. Usov, F. Ronning, L. Civale, E. Nazaretski, G. F. Chen, W. Yu, J. D. Thompson, R. Movshovich
本文报道了质子辐照产生的随机点缺陷对超导Ca $_{0.5}$ Na $_{0.5}$ Fe $_2$ As $_2$单晶超流密度$ρ_{s}$的显著影响。抑制的大小是通过使用磁力显微镜测量与温度相关的磁穿透深度$λ(T)$来推断的。我们的研究结果表明，辐射剂量为2 $\times10^{16}$ cm $^{-2}$由3 MeV的质子产生的超导临界温度$T_{c}$的减少约10%的结果。%，而上临界场的斜率没有明显的变化。相反，$ρ_{s}(0)$被抑制约60%。Abrikosov-Gorkov理论的这种崩溃可以用所谓的“瑞士奶酪模型”来解释，该模型解释了类似于瑞士奶酪中的孔的点缺陷附近的序参数的空间抑制。上临界场的斜率和穿透深度$λ(T/T_{c})/λ(0)$在辐照前后表现出相似的温度依赖性。这可能是由于Ca $_{0.5}$ Na $_{0.5}$ Fe $_2$ As $_2$的高度无序性质与大的带内和同时带间散射以及短相干长度超导性的$s^\pm$波性质的组合。
英文摘要：
We report on the dramatic effect of random point defects, produced by proton irradiation, on the superfluid density $ρ_{s}$ in superconducting Ca$_{0.5}$Na$_{0.5}$Fe$_2$As$_2$ single crystals. The magnitude of the suppression is inferred from measurements of the temperature-dependent magnetic penetration depth $λ(T)$ using magnetic force microscopy. Our findings indicate that a radiation dose of 2$\times10^{16}$cm$^{-2}$ produced by 3 MeV protons results in a reduction of the superconducting critical temperature $T_{c}$ by approximately 10%. % with no appreciable change in the slope of the upper critical fields. In contrast, $ρ_{s}(0)$ is suppressed by approximately 60%. This break-down of the Abrikosov-Gorkov theory may be explained by the so-called "Swiss cheese model", which accounts for the spatial suppression of the order parameter near point defects similar to holes in Swiss cheese. Both the slope of the upper critical field and the penetration depth $λ(T/T_{c})/λ(0)$ exhibit similar temperature dependences before and after irradiation. This may be due to a combination of the highly disordered nature of Ca$_{0.5}$Na$_{0.5}$Fe$_2$As$_2$ with large intraband and simultaneous interband scattering as well as the $s^\pm$-wave nature of short coherence length superconductivity.
Effects of electron irradiation on resistivity and London penetration depth of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ ($x \leq$ 0.34) iron - pnictide superconductor
用2.5 MeV电子以高达5.2 $\times$ 10 $^{19}$电子/cm $^2$的剂量辐照，在Ba $_{1-x}$ K $_x$ Fe $_2$单晶中引入点状缺陷。（$T_c=$ 14 K），$x=$ 0.26（$T_c=$ 32 K）和0.34（$T_c=$ 39 K）通过探测非磁散射对电阻率$ρ(T)$和伦敦穿透深度$ λ(T)$的影响来研究超导间隙结构。对于所有的组合物，照射抑制超导转变温度，$T_c$和增加的电阻率。$λ(T)$的低温行为最好用幂律函数$Δλ(T) = A(T/T_c)^n$来描述.虽然$T_c$的实质性抑制支持$s_{\pm}$配对机制，但在接近最佳掺杂的样品中，$x=$ 0.26和0.34，指数$n$保持高（$n \geq 3$），表明稳健的全超导带隙。对于表现出超导性和长程磁性共存的$x=$ 0.19组合物，$T_c$的抑制快得多，并且指数$n$朝向$n$ = 2的脏极限降低。在该样品中，照射还抑制了结构/磁性转变的温度，$T_{sm}$，从103 K到98 K，与磁序的巡回性质一致。我们的研究结果表明，欠掺杂的组合物，特别是在共存制度是最容易受到非磁散射，并意味着在多频带Ba $_{1-x}$ K $_x$ Fe $_2$作为$_2$超导体，带间带内配对强度的比率，以及相关的间隙各向异性，增加后，从最佳掺杂的偏离。
Zero-field superfluid density in d-wave superconductor evaluated from the results of muon-spin-rotation experiments in the mixed state
本文报道了用μ子自旋旋转（\muSR）方法测量最佳掺杂铜酸盐超导体（BiPb）_2（SrLa）_2CuO_6+δ（OP Bi 2201）的面内磁穿透λ_{ab}。我们发现，在非常规的$d-$波超导体（如OP Bi 2201）中，在各种磁场中进行的\muSR实验允许评估零场磁穿透深度λ_0，其与零场超流密度ρ_s \propto λ_0^-2有关。
We have characterized an electron-irradiated Ba1-xKxFe2As2 (x = 0.53) single-crystal using two different experimental techniques: magneto-optic measurements and microwave measurements. The crystal has been measured before as well as after the 2.5 MeV electron irradiation process. After irradiation it was annealed in a number of steps, between 90 deg C and 180 deg C, and measured after each annealing step. Most microwave measurements were performed by means of a copper cavity, taking advantage of the TE011 and TM110 modes, allowing for the determination of the London penetration depths changes …
As the most successful microscopic superconductivity theory, Bardeen-Cooper-Schrieffer(BCS) theory has a very peculiar prediction: at zero temperature, only a fraction of electrons within an energy shell form Cooper pair and condense, but all electrons participate to form a macroscopic superfluid and contribute to the superfluid density (inverse square of penetration depth). Very recently, this prediction was challenged by directly measuring the penetration depth upon doping in overdoped cuprates. (Bozovic et al., 2016) Here, we show that such a counter-intuitive prediction of BCS theory is no…
Microwave Surface-Impedance Measurements of the Magnetic Penetration Depth in Single Crystal Ba1-xKxFe2As2 Superconductors: Evidence for a Disorder-Dependent Superfluid Density
本文报道了用高灵敏度微波测量掺空穴铁基超导体Ba $_{1-x}$ K $_x$ Fe $_2$ As $_2$（$x\approx 0.55$）单晶中的面内穿透深度$λ_{ab}$和准粒子散射率$1/τ$。虽然幂律温度依赖性的$λ_{ab}$与功率$\sim 2$被发现在晶体中与大$1/τ$，我们观察到指数温度依赖性的超流密度与存在的完全打开的两个间隙，我们研究的最干净的晶体。这种差异可能是晶体中固有的无序程度不同的结果。我们还发现低温散射率与准粒子密度之间存在线性关系，这与d波铜氧化物超导体的情况形成了鲜明的对比。这些结果表明铁砷化物的内在无节序参量。
Temperature-dependent London penetration depth, $λ(T)$, of a high quality optimally-doped $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{7-δ}$ single crystal was measured using tunnel-diode resonator. Controlled artificial disorder was induced at low-temperature of 20~K by 2.5 MeV electron irradiation at accumulating large doses of $3.8\times10^{19}$ and $5.3\times10^{19}$ electrons per $\textrm{cm}^{2}$. The irradiation caused significant suppression of the superconductor's critical temperature, $T_{c}$, from 94.6 K to 90.0 K, and then to 78.7 K, respectively. The low-temperature behavior of $λ\left(T…
Nodal Protectorate: A Unified Theory of the ab-plane and c-axis Penetration Depths of Underdoped cuprates
我们制定了一个模型描述的掺杂（$x$）和温度（$T$）依赖的$ab$平面和c轴的渗透深度的铜氧化物超导体。该模型采用了抑制的超流密度与欠掺杂的系统接近莫特-哈伯德绝缘状态，通过增加一个d-波BCS模型的现象学电荷重整化因子，是消失的小状态远离节点的d-波对电位，但接近团结的节点附近。的c轴穿透深度内捕获的CuO $_2$平面之间的非相干电子隧穿的模型。应用这个模型的高纯度单晶YBa $_2$ Cu $_3$ O $_{6+δ}$的最新实验数据意味着存在一个“节点保护区”，一个$k$ -空间区域的节点附近的大小成比例地减少到$x$，其中d波准粒子保持尖锐，即使系统摇摇欲坠的边缘成为绝缘体。超流体密度，这是非常小的这些样本，也似乎完全来自这些保护节点区域。
Field Induced Reduction of the Low Temperature Superfluid Density in YBa2Cu3O6.95
利用一种新型的高磁场（8 T）μ子自旋谱仪测量了YBa 2 Cu 3 O 6. 95的面内磁穿透深度随温度的变化。在低H和低T下，穿透深度表现出与d_x^2-y^2波超导体的能隙相关的特征线性T依赖性。然而，在较高的磁场下，穿透深度在低T下基本上与温度无关。我们讨论了可能的解释，这个令人惊讶的新功能在低能量激发光谱。
London penetration depth in Ba(Fe$_{1-x}$T$_x$)$_2$As$_2$ (T=Co, Ni) superconductors irradiated with heavy ions
用Pb离子辐照Ba（Fe $_{1-x}$ T $_x$）$_2$ As $_2$（T=Co，Ni）单晶，研究了无序对面内伦敦穿透深度$λ(T)$的影响。随着辐照剂量的增加，超导转变温度$T_c$单调下降，而对转变宽度影响不大。在Co和Ni掺杂体系中，我们发现了一个幂律行为，即$Δλ(T) \propto T^n$，其指数$n$随无序度的增加而系统地减小。这一观察，支持的理论分析，最终指向一个无节点的$s^\pm$状态与成对断裂杂质散射（带间）的强度是玻恩和幺正极限之间的中间。
Investigation of the Superconducting Gap Structure in SrFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$ by Magnetic Penetration Depth and Flux Flow Resistivity Analysis
测量了掺磷铁基超导体SrFe $_2$（As $_{1-x}$ P $_{x}$）$_2$单晶（$x=0.30$，$T_c=25 \mathrm{K}$）的微波表面阻抗，获得了单晶中的超流密度和磁通流电阻率。在低温下，超流密度$n_s (T)/n_s(0)$服从幂律$n_s (T)/n_s (0)=1-C(T/T_c)^n$，分数指数为$n=1.5$-1.6。在低磁场下，磁通流电阻率显著增强。这些功能是一致的存在与线节点的间隙和无节点的间隙与深最小。实验中观察到的SrFe $_2$（As $_{1-x}$ P $_{x}$）$_2$和BaFe $_2$（As $_{1-x}$ P $_{x}$）$_2$超导能隙结构的显著差异，对阐明铁基超导机制具有重要意义。
Irradiation with electrons is an efficient approach to inducing a large number of defects with a minimal impact on the material itself. Analysis of the energy transfer from an accelerated particle smashing into the crystal lattice shows that only electrons with MeV energies produce point defects in the form of interstitial ions and vacancies that form perfect scattering centers. Here, we investigate the changes in the resistive characteristics of YBCO single crystals from the 1-2-3 system after several steps of low-temperature irradiation with $0.5-2.5$\,MeV electrons and irradiation doses of …
We report measurements of the in-plane London penetration depth $λ$ in single crystals of the $α$-PdBi$_{2}$ superconductor --- the $α$-phase counterpart of the putative topological superconductor $β$-PdBi$_{2}$, down to 0.35~K using a high-resolution tunnel-diode-based technique. Both $λ$ and superfluid density $ρ_{s}$ exhibit an exponential behavior for $T\leq$ 0.35$T_{c}$, with $Δ(0)/k_{B}T_{c}\sim$2.0, $ΔC/γT_{c}$$\sim$2.0 and $λ(0)$$\sim$140~nm, showing that $α$-PdBi$_{2}$ is a moderately-coupling, fully-gapped superconductor. The values of $Δ(0)$ and $ΔC/γT_{c}$ are consistent with each …
Superconductivity in the topological non-trivial Dirac semimetal PdTe$_2$ was recently shown to be type-I. We here report measurements of the relative magnetic penetration depth, $ Δλ$, on several single crystals using a high precision tunnel diode oscillator technique. The temperature variation $Δλ(T)$ follows an exponential function for $T/T_c < 0.4$, consistent with a fully-gapped superconducting state and weak or moderately coupling superconductivity. By fitting the data we extract a $λ(0)$-value of $\sim 500$~nm. The normalized superfluid density is in good agreement with the computed cur…
Local measurement of the penetration depth in the pnictide superconductor Ba(Fe$_{0.95}$Co$_{0.05}$)$_2$As$_2$
用磁力显微镜（MFM）和扫描SQUID法测量了Ba（Fe $_{0.95}$ Co $_{0.05}$）$_2$ As $_2$单晶从0.4 K到临界温度$T_c=18.5$ K的局域超流密度$ρ_{s}$。我们观察到，穿透深度$λ$的变化速度比以前公布的温度慢约10倍，可以很好地描述一个干净的两带完全带隙模型的依赖。我们证明，MFM可以测量的重要和难以确定的绝对值的$λ$，以及获得其温度依赖性和空间均匀性。我们发现$ρ_{s}$是均匀的，尽管高度无序的涡旋钉扎。
Aligned crystallite powder of NdFeAsO$_{0.86}$F$_{0.14}$: magnetic hysteresis and penetration depth
报道了磁取向NdFeAsO $_{0.86}$ F $_{0.14}$粉末的基面临界电流和超流密度。该样品具有沿外场永久定向的c轴的单个微晶颗粒。在高场磁不可逆性建议强磁通钉扎的基面临界电流，与单调的字段依赖性和没有证据的“鱼尾”效应。小颗粒提供了\textit{dc}通量渗透的灵敏指示器，并允许分析$ab-$平面伦敦渗透深度$λ_{ab,\mathrm{L}}$的温度依赖性，其在低$T$下是二次的。该特征可能不一定是由于间隙中的节点，而是可能是强对断裂的标志。$λ_{ab,\mathrm{L}}$的绝对量的定量测定由于需要精确了解粒度分布而受到阻碍。
