The superconducting phase transition in YBa$_{2}$Cu$_{3}$O$_{7-\textit{$δ$}}$(YBCO) thin film samples doped with non-superconducting nanodot impurities of CeO$_{2}$ are the focus of recent high-temperature superconductor studies. Non-superconducting holes of the superconducting lattice induce a bound-state of circulating paired electrons. This creates a magnetic flux vortex state. Examining the flow of free-electrons shows that these quantized magnetic flux vortices arrange themselves in a self-assembled lattice. The nanodots serve to present structural properties to constrict the "creep" of these flux vorticies under a field response in the form of a pinning-force enhancing the critical current density after phase transition. In this work, a model for characterizing the superconducting phase by the work done on electron pairs and chemical potential, following the well-known theories of Superconductivity (Bardeen-Cooper-Scheifer \& Ginzburg-Landau), is formulated and tested.A solution to the expression for the magnetic flux, zero net force and pair velocity will generate a setting for the optimal deposition parameters of number density, growth geometry and mass density of these nanodot structures.
We have successfully synthesized the c-axis oriented YBa2Cu4O8 (Y-124) film on a SrTiO3 (1 0 0) substrate via a coprecipitation and a dip-coating method. The precipitations including Y, Ba and Cu ions were obtained using their metal nitrates solution and the aqueous solution of sodium hydroxide and oxalic acid. Superconducting transition of the synthesized film was observed at 64-70 K corresponding to bulk Y-124 in the magnetization and resistance measurement. The developed method is suitable to synthesize superconducting Y-124 films for technological applications.
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…
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, …
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…
YBa$_{2}$Cu$_{3}$O$_{7-δ}$ coated conductors (CCs) have achieved high critical current densities ($\textit{J}_{c}$) that can be further increased through the introduction of additional defects using particle irradiation. However, these gains are accompanied by increases in the flux creep rate, a manifestation of competition between the different types of defects. Here, we study this competition to better understand how to design pinning landscapes that simultaneously increase $\textit{J}_{c}$ and reduce creep. CCs grown by metal organic deposition show non-monotonic changes in the temperature-…
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。
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 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…
It is known that solid-state reaction in high-pressure oxygen can stabilize high-oxidation phases of Y-Ba-Cu-O superconductors in powder form. We extend this superoxygenation concept of synthesis to thin films which, due to their large surface-to-volume ratio, are more reactive thermodynamically. Epitaxial thin films of $\rm{YBa_2Cu_3O_{7-δ}}$ grown by pulsed laser deposition are annealed at up to 700 atm O$_2$ and 900$^\circ$C, in conjunction with Cu enrichment by solid-state diffusion. The films show clear formation of $\rm{Y_2Ba_4Cu_7O_{15-δ}}$ and $\rm{Y_2Ba_4Cu_8O_{16}}$ as well as region…
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 …
Combined action of weak and strong pinning centers on the vortex lattice complicates magnetic behavior of a superconductor since temperature and magnetic field differently affect weak and strong pinning. In this paper we show that contributions of weak and strong pinning into magnetization of the layered superconductor YBa$_2$Cu$_3$O$_{7-δ}$ can be separated and analyzed individually. We performed a careful analysis of temperature behavior of the relaxed superconducting current $J$ in YBa$_2$Cu$_3$O$_{7-δ}$ films which revealed two components of the current $J = J_1 +J_2$. A simple method of s…
