The Vortex Glass phase has been unequivocally identified by analyzing the non linear magnetic response of type II superconductors. The method here introduced, more effective than the study of direct transport measurements, is based on a combined frequency dependence analysis of the real and imaginary part of the 1st and 3rd harmonics of the AC magnetic susceptibility. The analysis has been performed by taking into account both the components and the Cole-Cole plots (i.e. the imaginary part as a function of the real part). Numerical simulations have been used to individuate the fingerprints of the magnetic behaviour in the Vortex Glass phase. These characteristics allowed to distinguish the Vortex Glass phase from the other disordered phases, even those showing similar electrical properties. Finally, this method has been successfully applied to detect the Vortex Glass Phase in an YBCO bulk melt-textured sample.
The glass-like vortex distribution in pulsed laser deposited YBCO thin films is observed by scanning superconducting quantum interference device microscopy and analysed for ordering after cooling in magnetic fields significantly smaller than the Earth's field. Autocorrelation calculations on this distribution show a weak short-range positional order, while Delaunay triangulation shows a near-complete lack of orientational order. The distribution of these vortices is finally characterised as an isotropic vortex glass. Abnormally closely spaced groups of vortices, which are statistically unlikel…
Beta-NMR has been used to study vortex lattice disorder near the surface of the high-Tc superconductor YBCO. The magnetic field distribution from the vortex lattice was detected by implanting a low energy beam of highly polarized 8Li into a thin overlayer of silver on optimally doped, twinned and detwinned YBCO samples. The resonance in Ag broadens significantly below the transition temperature Tc as expected from the emerging field lines of the vortex lattice in YBCO. However, the lineshape is more symmetric and the dependence on the applied magnetic field is much weaker than expected from an…
Angular dependent vortex pinning mechanisms in YBCO coated conductors and thin films
我们提出了一个角度依赖的临界电流密度在IBAD MgO和单晶MgO和SrTiO 3衬底上沉积的YBa 2 Cu 3 O 7薄膜的比较研究。我们确定了三个角度制度，钉扎是由不同类型的相关和不相关的缺陷。我们发现，这些制度是存在于所有情况下，表明钉扎机制是相同的，但它们的扩展和特性是样品依赖的，反映了纹理和缺陷密度的定量差异。特别地，IBAD上的膜的更多缺陷性质变成优点，因为它导致更强的涡旋钉扎，表明单晶上的膜的临界电流密度不是IBAD涂覆的导体的性能的上限。
Fascination with glassy states has persisted since Fisher introduced the vortex-glass as a new thermodynamic phase that is a true superconductor that lacks conventional long-range order. Though Fisher's original model considered point disorder, it was later predicted that columnar defects (CDs) could also induce glassiness -- specifically, a Bose-glass phase. In YBa$_2$Cu$_3$O$_{7-x}$ (YBCO), glassy states can cause distinct behavior in the temperature ($T$) dependent rate of thermally activated vortex motion ($S$). The vortex-glass state produces a plateau in $S(T)$ whereas a Bose-glass can t…
We present a microwave study of the angular dependence of the flux-flow resistivity $ρ_{ff}$ and of the pinning constant $k_p$ in YBCO thin films containing BZO nanorods. We find that BZO nanorods are very efficient pinning centers, even in tilted fields. We find that $ρ_{ff}$ is a scaling function of a reduced field $H/f(θ)$. We extend a model for the anisotropic motion of vortices in uniaxially anisotropic superconductor, able to describe the experimental $f(θ)$ on the basis of only the intrinsic anisotropy of YBCO. The pinning constant $k_p$, by contrast, exhibits different field dependence…
Equilibrium First-Order Melting and Second-Order Glass Transitions of the Vortex Matter in Bi$_2$Sr$_2$CaCu$_2$O$_8$
通过测量存在涡旋“振动”时的局部\emph{equilibrium}磁化强度$M(H,T)$，绘制了BiPDMATHABMN Sr $_2$ CaCu $_2$ O $_8$的热力学$H-T$相图。两个同样尖锐的一级磁化步骤显示在一个单一的温度扫描，体现了液-固-液序列。此外，二阶玻璃化转变线显示的平衡$M(T)$斜率急剧突破。一阶和二阶线相交在中间温度，表明存在四个阶段：布拉格玻璃和涡旋晶体在低场，玻璃和液体在较高的领域。
We found a finite temperature glass transition in the absence of quenched disorder in frustrated Josephson junction arrays (JJA) on a square lattice with anisotropic Josephson couplings by numerical simulations. The vortexes develop zigzag stripes into the direction of weaker coupling at low temperatures. The whole amorphous vortex solid can flow smoothly into the direction of stronger coupling by non-trivial soft modes. As the result the macroscopic phase coherence is destroyed being reminiscent of vortex flow in pure bulk superconductors or spin-chirality decoupling in frustrated magnets. On…
At low enough temperatures and high densities, the equilibrium configuration of an ensemble of ultrasoft particles is a self-assembled, ordered, cluster-crystal. In the present work we explore the out-of-equilibrium dynamics for a two-dimensional realization, which is relevant to superconducting materials with multi-scale intervortex forces. We find that for small temperatures following a quench, the suppression of the thermally-activated particle hopping hinders the ordering. This results in a glass transition for a monodispersed ensemble, for which we derive a microscopic explanation in term…
The Abricosov vortex and bundles dynamics was experimentally investigated in Earth's magnetic field range. Isothermal relaxation features in YBCO single crystal samples with strong pinning centers were studied for different sample-field orientation. The normalized relaxation rate S obtained allowed to estimate the effective pinning potential U in the bulk of the YBCO sample and its temperature dependence, as well as the critical current density Jc. A comparison between the data obtained and the results for similar measurements in significantly higher magnetic fields was performed. To compare d…
The defect-rich morphology of YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (YBCO) thin films leads to a glass-like arrangement of Abrikosov vortices which causes the resistance to disappear in vanishing current densities. This vortex glass consists of entangled vortex lines and is identified by a characteristic scaling of the voltage-current isotherms. Randomly distributed columnar defects stratify the vortex lines and lead to a Bose glass. Here, we report on the observation of an ordered Bose glass in a YBCO thin film with a hexagonal array of columnar defects with 30 nm spacings. The periodic pinning landscap…
Change of strength of vortex pinning in YBCO due to BaZrO_3 inclusions
我们探测的短程钉扎性能与应用程序的微波电流在很高的驱动频率（47.7 GHz）上的YBa $_2$铜$_3$ O $_{7-δ}$薄膜和没有亚微米BaZrO $_3$夹杂物。我们探索的温度和字段范围60 K $<T<T_c$和0 $<μ_0H<$ 0.8 T，沿c轴施加的字段。相对于纯YBa $_2$ Cu $_3$ O $_{7-δ}$，磁场引起YBa $_2$ Cu $_3$ O $_{7-δ}$ /BaZrO $_3$中微波电阻率$Δρ_1(H)+\mathrm{i}Δρ_2(H)$的小得多的增加。$Δρ_1(H)$在纯YBa $_2$ Cu $_3$ O $_{7-δ}$中略微呈超线性（表明热活化的可能贡献），但在YBa $_2$ Cu $_3$ O $_{7-δ}$ /BaZrO $_3$中呈线性或亚线性（表明BaZrO $_3$夹杂物可能抑制热活化）。这些特性一直保持到接近$T_c$。我们讨论了我们的数据中的比例$r=ΔX_s'(H)/ΔR_s'(H)$在混合状态下的微波表面阻抗模型的框架。在$_2$ O $_{7-δ}$ /BaZrO $_3$中发现了大的$r$，几乎没有场依赖性。相比之下，在纯$_2$ O $_{7-δ}$中发现较小的值和较强的场依赖性.我们讨论了不同的场依赖的钉扎常数。
Absence of a True Vortex-Glass Phase above the Bragg Glass Transition Line in Bi-2212
在对Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$（Bi-2212）单晶的磁性测量中，发现在$S-H$和$S-T$曲线上都有一个具有动力学特征的通用峰，S为磁弛豫速率。在较高的磁场下，特征指数$μ$变为负值，结合$logE$与$ logj$的正曲率和基于二维涡旋玻璃理论或塑性蠕变理论的标度，我们得出结论：当$j\to 0$时，第二峰以上的涡旋运动是塑性的，在有限温度下Bi-2212中不存在涡旋玻璃相。S的峰值被解释为不同亚稳涡旋态之间的交叉。
Square arrays of sub-micrometer columnar defects in thin YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (YBCO) films with spacings down to 300 nm have been fabricated by a He ion beam projection technique. Pronounced peaks in the critical current and corresponding minima in the resistance demonstrate the commensurate arrangement of flux quanta with the artificial pinning landscape, despite the strong intrinsic pinning in epitaxial YBCO films. Whereas these vortex matching signatures are exactly at predicted values in field-cooled experiments, they are displaced in zero-field cooled, magnetic-field ramped experime…
We show that in type-II superconductors a magnetic field applied transversely to correlated columnar disorder, drives a phase transition to a distinct "smectic" vortex glass (SmVG) state. SmVG is characterized by an infinitely anisotropic electrical transport, resistive (dissipationless) for current perpendicular to (along) columnar defects. Its positional order is also quite unusual, long-ranged with true Bragg peaks along columnar defects and logarithmically rough vortex lattice distortions with quasi-Bragg peaks transverse to columnar defects. For low temperatures and sufficiently weak colu…
The vortex liquid-to-glass transition has been studied in Ba0.72K0.28Fe2As2, Ba0.9Co0.1Fe2As2, and Ba(Fe0.45Ni0.05)2As2 single crystal with superconducting transition temperature, Tc = 31.7, 17.3, and 18 K, respectively, by magnetoresistance measurements. For temperatures below Tc, the resistivity curves were measured in magnetic fields within the range of 0 \leq B \leq 13 T, and the pinning potential was scaled according to a modified model for vortex liquid resistivity. Good scaling of the resistivity ρ(B, T) and the effective pinning energy U0(B,T) was obtained with the critical exponents s…
An epitaxial NdFeAs(O,F) thin film of 90 nm thickness grown by molecular beam epitaxy on MgO single crystal with Tc = 44.2 K has been investigated regarding a possible vortex glass-liquid tran-sition. The voltage-current characteristics show excellent scalability according to the vortex-glass model with a static critical exponent ν of around 1.35 and a temperature-dependent dynamic exponent z increasing from 7.8 to 9.0 for the investigated temperature range. The large and non-constant z values are discussed in the frame of 3D vortex glass, thermally activated flux motion, and inhomogeneity bro…
Evidence of first-order transition between vortex glass and Bragg glass phases in high-$T_{\rm c}$ superconductors with point pins: Monte Carlo simulations
本文用蒙特卡罗模拟研究了点钉存在下高$\vec{B}\parallel\vec{c}$超导体中涡旋玻璃相和布拉格玻璃相之间的相变。观察到有限的潜热和比热的$δ$函数峰，这清楚地表明这是一个热力学一级相变。熵跃变和林德曼数的值与熔化转变的值一致。层间相位差的大跳跃与Gaifullin { \it et al.}的Bi $_{2}$ Sr $_{2}$ CaCu $_{2}$ O $_{8+y}$的最近约瑟夫森等离子体共振实验一致。
The vortex lattice in a Type II superconductor provides a versatile model system to investigate the order-disorder transition in a periodic medium in the presence of random pinning. Here, using scanning tunnelling spectroscopy in a weakly pinned Co0.0075NbSe2 single crystal, we show that at low temperatures, the vortex lattice in a 3-dimensional superconductor disorders in two steps across the peak effect. At the onset of the peak effect, the equilibrium Bragg glass transforms into an orientational glass through the proliferation of dislocations. At a higher field, the dislocations dissociate …
