We study dynamic fluctuation effects of $YBa_2Cu_3O_{7-δ}$ thin films in zero field around $T_c$ by doing frequency-dependent microwave conductivity measurements at different powers. The length scales probed in the experiments are varied systematically allowing us to analyze data which are not affected by the finite thickness of the films, and to observe single-parameter scaling. DC current-voltage characteristics have also been measured to independently probe fluctuations in the same samples. The combination of DC and microwave measurements allows us to precisely determine critical parameters. Our results give a dynamical scaling exponent $z=1.55\pm0.15$, which is consistent with model E-dynamics.
We report on measurements of the doping dependence of the upper critical field $H_{c,2}$ in 50 nm thick YBa$_2$Cu$_3$O$_{7-δ}$ films. The films are untwinned and are characterized by a small in-plane compressive strain. We find that the $H_{c,2}$ shows a strong decrease in the underdoped region of the phase diagram, in agreement with what has been measured in relaxed single crystals. The origin of the decrease of $H_{c,2}$ in the underdoped regime is discussed within a scenario where charge density wave order competes with superconductivity. This demonstrates the potential of using thin films …
Thermal Conductivity Tensor in YBa$_2$Cu$_3$O$_{7-x}$: Effects of a Planar Magnetic Field
在T=13.8 K时，测量了YBaPDMATHABMM CuPDMATHABMN O $_{7-x}$孪晶的热导率张量随平行于CuOPDMATHABMM面的磁场与热流方向夹角$θ$的变化。根据序参量的d波配对对称性，分别记录了$κ_{xx}$和$κ_{xy}$的场角依赖性的四倍和两倍变化。在所研究的磁场范围内，横向热导率$κ^0_{xy}$的振荡幅度大于纵向热导率$κ^0_{xx}$的振荡幅度（$0 T $ $ \le B \le 9 $ $T$）.从我们的数据中，我们得到的数量是免费的非电子的贡献，他们让我们的实验结果与当前模型的准粒子运输的混合状态的比较。
Optical Conductivity of Ortho-II YBa$_2$Cu$_3$O$_6.5$
$_2$ O $_6.5$的Ortho-II相的特征在于空Cu和填充Cu-O b轴的周期性交替使晶胞在a方向上加倍。在完整的链中的额外的氧产生了一个有吸引力的潜力，在飞机上的孔。在新的布里渊区边界$k_x=\pm pi/2$，我们估计从LDA计算的间隙开口的平面带分裂成两个。使用一个平面模型，它对待的d-波超导平均场近似，我们表明，带间跃迁产生强烈的各向异性特征的光学电导率控制的区域在k空间接近（$π/2,π/2$）。该特征的边缘位置给出了该区域准粒子谱随温度变化的信息。双层分裂将显示为双边形状。
Universal critical behavior in single crystals and films of YBa$_2$Cu$_3$O$_{7-δ}$
我们用不同的样品和技术研究了最佳掺杂的$_2$ O $_{7-δ}$在零外磁场中的正常到超导相变。使用直流传输测量，我们发现，动态临界指数$z=1.54\pm0.14$，和静态临界指数$ν=0.66\pm0.10$为两个薄膜（当有限厚度的影响包括在数据分析）和单晶（其中有限厚度的影响是不重要的）。我们还测量了不同微波频率和不同功率下的薄膜，这使我们能够系统地探测不同的长度尺度，以避免有限厚度效应。还对微波实验中使用的膜进行了DC传输测量，以提供进一步的一致性检查。这些微波和DC测量产生的z值与其他结果$z=1.55\pm0.15$一致。忽略有限厚度、有限电流和有限频率效应可能是文献中先前报道的$ν$和$z$值范围较宽的原因。
Low Temperature Thermal Conductivity of High Purity YBa$_{2}$Cu$_{3}$O$_{6.99}$ in the Vortex State
本文研究了任意杂质势强度下d波超导体的低温热导率。通常的半经典方法中包含了涡的随机分布。涡旋准粒子散射占唯象，除了杂质散射。应用该理论对高纯度$_{2}$ O $_{6.99}$的最新数据表明，无论是在零场还是在外加磁场的存在下，都与实验非常吻合。我们发现，描述数据所需的杂质势的强度定性偏离酉或玻恩极限。
Anisotropic microwave conductivity of cuprate superconductors in the presence of CuO chain induced impurities
在动能驱动的超导机制下，研究了邻位Ⅱ型$_2$的微波电导各向异性.邻位-Ⅱ $_2$ $_3$ O $_{6.50}$的特征在于填充和空$\hat{b}$轴CuO链的周期性交替。考虑CuO链诱导的扩展各向异性杂质散射，基于准粒子激发和散射过程的节块近似，再现了邻位Ⅱ型$_2$微波电导各向异性的主要特征，包括$\hat{a}$轴和$\hat{b}$轴微波电导的能量和温度依赖性的强度和线形.我们的研究结果也证实了$\hat{b}$轴CuO链诱导杂质是各向异性的主要来源。
Theory of optical conductivity in detwinned YBa$_2$Cu$_3$O$_{y}$
从理论上研究了$_2$ O $_3$的链状和面内光学电导。我们阐述了链是超导的$y>6.67$，而绝缘的$y<6.67$由于平面链耦合和反铁磁序之间的竞争，对应于一个超导体-绝缘体转变。超导态的面内谱在低频处出现一个新的峰，而正常态的面内谱在低频处消失，这也是由于平面和链之间的耦合。我们的设想令人满意地解释了最近的实验。
Persistence of superconducting condensate far above the critical temperature in YBa$_2$(Cu,Zn)$_3$O$_y$ revealed by $c$-axis optical conductivity measurements for several Zn concentrations and carrier doping levels
YBa$_2$Cu$_3$O$_{7-δ}$ is a good candidate to systematically study high-temperature superconductivity by nanoengineering using advanced epitaxy. An essential prerequisite for these studies are coherently strained YBa$_2$Cu$_3$O$_{7-δ}$ thin films, which we present here using NdGaO$_3$ (110) as a substrate. The films are coherent up to at least 100 nm thickness and have a critical temperature of 89$\pm$1 K. The $a$ and $b$ lattice parameters of the YBa$_2$Cu$_3$O$_{7-δ}$ are matched to the in-plane lattice parameters of NdGaO$_3$ (110), resulting in a large reduction of the orthorhombicity of t…
Fermi surface arcs and the infrared conductivity of underdoped YBa$_{2}$Cu$_{3}$O$_{6.50}$
我们重新分析了欠掺杂$_{2}$（YBCO $_{6.50}$）的面内远红外电导率的数据，在这个模型中，赝能隙在费米面的一部分上打开，而剩余的未被覆盖的部分与温度成正比.我们的模型的动机来自于最近的角度分辨光电子能谱数据欠掺杂的Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$（Bi-2212），这揭示了费米表面上的弧的存在。我们发现的光学数据是一致的电弧形成。此外，我们发现一些证据表明，电子状态下失去的赝能隙$Δ_{pg}$恢复的能量区域，至少在$T_c$附近的温度。
We present a detailed study of the electrical transport properties of YBa2Cu3O7-δ thin film. The irreversibility fields (μ_0 H_irr), upper critical fields (μ_0 H_C2), penetration depths (λ) and coherence lengths (ξ ) of the YBa2Cu3O7-δ materials are deduced from the resistivity curves. Itis observed that μ_0 H_irr, μ_0 H_C2 and ΔTc of the film strongly depend on the direction and strength of the field. The coherence length ξ (0) and penetration depth λ (0) values at T = 0 K has been calculated from the irreversibility fields (μ_0 H_irr) and upper critical fields (μ_0 H_C2) respectively. Based …
Critical currents in vicinal YBa$_2$Cu$_3$O$_{7-δ}$ films
大多数测量的临界电流密度在YBa $_2$ Cu $_3$ O $_{7-δ}$薄膜的日期已进行的薄膜中的\textit{c}轴是垂直于膜表面生长。对于这样的膜，分析$j_c$对磁场角度的依赖性是复杂的。$j_c$的角场依赖性的外部贡献的影响，如测量几何形状和钉扎中心的布置，与那些固有的由于材料的各向异性。因此，很难区分基于对\textit{c}轴膜的角临界电流密度测量的所提出的FLL结构模型。生长在误切（邻位）衬底上的薄膜具有降低的测量对称性，从而提供了对临界电流各向异性的更深入了解。本文综述了$_2$中$_3$随磁场角度变化的研究结果。本文介绍了在一系列邻位衬底上生长的$_2$薄膜的测量结果，并对$_2$中的FLL结构和维数进行了解释。有强有力的证据表明，在磁通线晶格的结构取决于磁场的大小，方向和温度的转变。因此，一个简单的标度律不能，本身，描述所观察到的临界电流各向异性在YBa $_2$ Cu $_3$ O $_{7-δ}$。实验获得的$j_c(θ)$行为的YBCO成功地描述在一个扭曲的旋涡结构的字段施加近平行于\textit{a-b}平面。
Angle Dependence of the Transverse Thermal Conductivity in YBa$_2$Cu$_3$O$_7$ single crystals: Doppler Effect vs. Andreev scattering
在不同的磁场和温度下，测量了孪晶和非孪晶YBa $_2$ Cu $_3$ O $_7$单晶的横向热导率$κ_{xy}$随平行于CuO $_2$面的磁场与热流方向夹角$θ$的变化。对于这两种晶体，我们观察到一个明确的双重变化的场角依赖性的$κ_{xy}(θ) = - κ^0_{xy}(T,B) \sin(2θ)$。我们发现振荡幅度$κ^0_{xy}$依赖于温度和磁场。我们的结果表明，$κ^0_{xy} = a B \ln(1/(bB))$与温度和样品依赖的参数$a$和$b$。我们讨论了我们的结果的Andreev散射的准粒子的旋涡和最近提出的理论的基础上的多普勒频移的准粒子谱。
a-b plane optical conductivity in YBa_2Cu_3O_{7-delta} above and below T*
作为温度和掺杂的函数的孪晶和非孪晶的YBa $_{2}$ Cu $_{3}$ O $_{7-δ}$的a-b平面光学电导率$σ_{ab}$的分析表明，在一个明确定义的温度T* 以下，在光谱中的下降系统地出现分离的红外电荷激发光谱成两个组件具有不同的能量尺度。从单调的行为在$σ_{ab}$的变化被认为是并发的声子异常的拉曼和红外光谱T* 以下的发病。的光学数据建议是一个不均匀的载流子分布的外观，而不是一个简单的间隙低于T* 的电荷激发，解释是一致的，与最近的角分辨光电子能谱和电子拉曼光谱的开放的证据。我们发现，T* 以下的行为和没有任何异常，在Tc可以解释假设一个玻色-爱因斯坦凝聚的预制对。
Evidence for a pseudogap in underdoped $Bi_2Sr_2CaCu_2O_{8+δ}$ and $YBa_2Cu_3O_{6.50}$ from in-plane optical conductivity measurements
欠掺杂Bi $_{2}$ Sr $_{2}$ CaCu $_{2}$ O $_{8+δ}$（Bi-2212）和ortho Ⅱ YBa $_{2}$ Cu $_{3}$ O $_{6.5}$的面内光学自能数据的实部包含了关于赝能隙的新的重要信息。使用理论模型的方法，我们发现，在赝能隙$Δ_{pg}$以下的态密度损失伴随着一个堆积以上的能量。的堆积，随着一个尖锐的模式在玻色子光谱函数导致一个不寻常的快速增加的光散射率和一个典型的倾斜的峰值在实部的光学自能。这些特征在最佳掺杂和过掺杂样品中没有发现，并且代表了迄今为止在面内光学电导率中的赝隙开口的最清晰的签名。
We have discovered two novel types of planar defects that appear in heteroepitaxial YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO123) thin films, grown by pulsed-laser deposition (PLD) either with or without a La$_{2/3}$Ca$_{1/3}$MnO$_3$ (LCMO) overlayer, using the combination of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging and electron energy loss spectroscopy (EELS) mapping for unambiguous identification. These planar lattice defects are based on the intergrowth of either a BaO plane between two CuO chains or multiple Y-O layers between two CuO$_2$ planes, resu…
Higher harmonics of ac voltage response in narrow strips of YBa2Cu3O7 thin films: Evidence for strong thermal fluctuations
我们报告的测量高次谐波的交流电压响应的条带的YBa 2 Cu 3 O 7薄膜作为温度，频率和交流电流振幅的函数。发现局部电压的三次（五次）谐波在超导转变温度处呈现负（正）峰，并且其幅度与一次（欧姆）谐波的斜率（导数）密切相关。峰值实际上不依赖于频率，并且没有检测到偶次（二次或四次）谐波。所观察到的数据可以解释在交流电流引起的样品温度的热调制添加到强的热激活的波动在过渡区。
The oxygen deficiency $δ$ in YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) plays a crucial role for affecting high-temperature superconductivity. We applied (coincident) Doppler broadening spectroscopy of the electron-positron annihilation line to study in situ the temperature dependence of the oxygen concentration and its depth profile in single crystalline YBCO film grown on SrTiO$_3$ (STO) substrates. The oxygen diffusion during tempering was found to lead to a distinct depth dependence of $δ$, which is not accessible using X-ray diffraction. A steady-state reached within a few minutes is defined by both, …
In the present work we study the growth by pulsed laser deposition of YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) films on the r-cut sapphire substrates. To improve the matching of the lattice parameters between the substrate and the film we use CeO$_{2}$ buffer layer, recrystallized prior to the deposition of YBCO. The optimal thickness and temperature of recrystallization of the buffer layer is first determined using atomic force microscopy (AFM) and X-ray diffraction. Next, we use the AFM to examine the dependence of YBCO film roughness on the film thickness, and we study the homogeneity of magnetic flux…
