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。
英文摘要：
We have studied the normal-to-superconducting phase transition in optimally-doped YBa$_2$Cu$_3$O$_{7-δ}$ in zero external magnetic field using a variety of different samples and techniques. Using DC transport measurements, we find that the dynamical critical exponent $z=1.54\pm0.14$, and the static critical exponent $ν=0.66\pm0.10$ for both films (when finite-thickness effects are included in the data analysis) and single crystals (where finite-thickness effects are unimportant). We also measured thin films at different microwave frequencies and at different powers, which allowed us to systematically probe different length scales to avoid finite-thickness effects. DC transport measurements were also performed on the films used in the microwave experiments to provide a further consistency check. These microwave and DC measurements yielded a value of z consistent with the other results, $z=1.55\pm0.15$. The neglect of finite-thickness, finite-current, and finite-frequency effects may account for the wide ranges of values for $ν$ and $z$ previously reported in the literature.
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 …
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…
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。
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…
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, …
Thin films of optimally-doped (001)-oriented YBa2Cu3O7-δ are epitaxially integrated on silicon (001) through growth on a single crystalline SrTiO3 buffer. The former is grown using pulsed-laser deposition and the latter is grown on Si using oxide molecular beam epitaxy. The single crystal nature of the SrTiO3 buffer enables high quality YBa2Cu3O7-δ films exhibiting high transition temperatures to be integrated on Si. For a 30 nm thick SrTiO3 buffer, 50 nm thick YBa2Cu3O7-δ films that exhibit a transition temperature of ~ 93 K, and a narrow transition width (< 5 K) are achieved. The integration…
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…
The Labusch Parameter of a Driven Flux Line Lattice in YBa$_2$Cu$_3$O$_7$ Superconducting Films
研究了驱动力对400 nm厚YBa $_2$ Cu $_3$ O $_7$超导薄膜中磁通线晶格场冷态弹性耦合（Labusch参数）的影响.我们发现没有驱动力的场冷态的FLL不处于平衡态。磁场施加在$0^\circ$和30 $^\circ$相对于CuO $_2$平面，得到的结果表明，在驱动电流密度小于临界的几个数量级的膜的弹性耦合的增强。我们的结果表明，在没有驱动力的情况下，场冷却后的FLL似乎处于相对有序的亚稳态。
Evidence of a critical hole concentration in underdoped YBa$_2$Cu$_3$O$_y$ single crystals revealed by $^{63}$Cu NMR
我们报道了一个$^{63}$ Cu NMR研究在去孪晶YBa $_2$ Cu $_3$ O $_y$单晶，重点是高度欠掺杂制度（y=6.35-6.6）。测量的光谱和自旋-晶格弛豫速率的$^{63}$铜揭示了静态秩序的出现在一个定义良好的起始温度$T_0$没有一个已知的序参数。虽然$T_0$随着空穴掺杂浓度$p$的增加而被快速抑制，但自旋赝能隙仅在$T_0\rightarrow 0$的掺杂含量附近和之上被识别。我们的数据表明，存在一个关键的空穴掺杂$p_c\sim 0.1$，这可能会控制静态秩序在$p<p_c$和自旋赝能隙在$p>p_c$。
Effect of varying material anisotropy on critical current anistropy in vicinal YBa$_2$Cu$_3$O$_{7-δ}$ thin films
高$T_{c}$铜氧化物超导体以其各向异性层状结构而闻名，某些材料确实趋向于Lawrence-Doniach超导体的极限。然而，YBa $_2$ Cu $_3$ O $_{7-δ}$具有比从其层间距预期的更小的各向异性。这是由于结构中的铜酸盐链。为了研究链氧对输运性质的影响，对完全氧化和脱氧的YBa $_2$ Cu $_3$ O $_{7-δ}$薄膜和最佳氧化的Y $_{0.75}$ Ca $_{0.2}$ Ba $_2$ Cu $_3$ O $_{7-δ}$薄膜进行了临界电流与外加场角的测量。在10个$^{\circ}$错切SrTiO $_3$衬底上生长薄膜，以观察到本征涡旋沟道效应。在依赖于场角的临界电流的研究中观察到的膜的涡旋沟道最小的形式被认为取决于膜氧化。涡流沟道效应取决于到弦-饼磁通线晶格的角相关交叉。所获得的结果似乎与Blatter等人的预测一致[Rev. Mod. Phys.，66（4）：1125（1994）]，增加的超导各向异性导致在较小的角度范围内存在扭结的弦-饼晶格。
We have grown and characterized 30 nm thick YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) films, deposited by pulsed laser deposition on both MgO (110) and SrTiO$_3$ (001) substrates, which induce opposite strain to the superconducting layer. By carefully tuning the in-situ post-annealing oxygen pressure, we achieved, in a reproducible way, films at different oxygen doping, spanning from the slightly overdoped down to the strongly underdoped region of the phase diagram. The transport properties of the films, investigated through resistance versus temperature measurements, are in perfect qualitative agreement …
The transverse (Hall) voltage in thin films of the high-temperature superconductor YBa$_{2}$Cu$_{3}$O$_{7-δ}$ with an artificial periodic pinning array is investigated. Columnar defect regions along the crystallographic $c$ axis, in which superconductivity is suppressed, are created by irradiation with He$^+$ ions through a silicon stencil mask. The commensurate arrangement of magnetic flux quanta with the artificial defect lattice is confirmed by maxima of the critical current and minima of the resistance, respectively. The magnetic field dependence of the transverse voltage reveals a commens…
Imaging the Anisotropic Nonlinear Meissner Effect in Nodal YBa$_{2}$Cu$_{3}$O$_{7-δ}$ Thin-Film Superconductors
我们通过（体）能隙节点和（表面）Andreev束缚态的非线性电动力学响应直接成像了非常规超导体中的各向异性非线性迈斯纳效应。将超导薄膜图案化成紧凑的自谐振螺旋结构，在射频范围内的谐振附近激发，并用聚焦激光束扰动扫描。在低温下，谐振器的电抗和电阻特性中的方向依赖非线性产生光响应，该光响应在超导体的费米表面上映射出节点或与这些节点相关联的束缚态的方向。该方法被证明在结超导体YBa $_{2}$ Cu $_{3}$ O $_{7-δ}$和结果是一致的体和表面的贡献与理论预测。
The resistivity and the Hall effect in the copper-oxide high-temperature superconductor YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (YBCO) are remarkably anisotropic. Using a thin film of YBCO grown on an off-axis cut SrTiO$_3$ substrate allows one to investigate these anisotropic transport properties in a planar and well-defined sample geometry employing a homogeneous current density. In the normal state, the Hall voltage probed parallel to the copper-oxide layers is positive and strongly temperature dependent, whereas the out-of-plane Hall voltage is negative and almost temperature independent. The results c…
We report the comprehensive comparative analysis of the upper critical magnetic fields $μ_{0}H_{c2}(0)$ obtained within Ginzburg-Landau and Werthamer-Helfand-Hohenberg theories for optimally-doped $YBa_2Cu_3O_{7-δ}$ thin films. For different orientations of the magnetic field, our calculations give 638 and 153 T for $μ_{0}H_{c2}(0)$, H || ab and $μ_{0}H_{c2}(0)$, H || c, respectively, when using $H_{c2}(0)$. For the first time, the temperature dependences of coherence lengths $ξ_{ab}(T)$ and $ξ_{c}(T)$ within proposed theories were determined using 50 and 90% criteria of the normal state resis…
A novel property of the quantum critical heavy fermion superconductor $β$-YbAlB$_4$ is revealed theoretically. By analyzing the crystalline electronic field (CEF) on the basis of the hybridization picture, odd parity CEF is shown to exist because of sevenfold configuration of B atoms around Yb, which breaks the local inversion symmetry. This allows onsite admixture of 4f and 5d wavefunctions with a pure imaginary coefficient, giving rise to the magnetic toroidal (MT) degree of freedom. By constructing a realistic minimal model for $β$-YbAlB$_4$, we show that onsite 4f-5d Coulomb repulsion driv…
Directional vortex pinning at microwave frequency in YBa$_{2}$Cu$_3$O$_{7-x}$ thin films with BaZrO$_3$ nanorods
研究了用脉冲激光烧蚀法从含5%（摩尔分数）BaZrO $_3$的靶上生长的YBaPDMATHABMM CuPDMATHABMN O $_{7-x}$薄膜的各向异性和定向钉扎效应. BaZrO $_3$夹杂物自组装得到沿c轴取向的纳米棒，从而为涡旋钉扎提供了优先方向。涡旋响应的方向性研究在高交流频率与复杂的微波响应在48 GHz，作为一个功能的应用领域和领域和c轴之间的角度$θ$。复杂的微波响应不表现出任何角度缩放，这表明YBa $_2$ Cu $_3$ O $_{7-x}$的结构各向异性的补充，至少另一个优选的取向。钉扎参数$r$显示定向钉扎的证据，在围绕c轴的宽范围的角度中有效（因此归因于BZO纳米柱）。
