A scanning superconducting quantum interference device (SQUID) microscope (SSM) is used to study the magnetic imaging of dynamic motion of quantized interlayer vortices induced by the Lorentz force in anisotropic high-Tc La_(1.87)Sr_(0.13)CuO_4 single crystals. It is found that 3 modes of flux motion switch depending on the transport current. By increasing the current a transition from the creep-like behavior of vortices to a steady flow of vortices was observed. Even higher current induced a continuous expansion of vortex-flow area indicating an inhomogeneous distribution of various pinning centers.
Magnetic-field-induced enhancement of the vortex pinning in the overdoped regime of La$_{2-x}$Sr$_x$CuO$_4$ : Relation to the microscopic phase separation
为了研究过掺杂高$T_{\rm c}$铜氧化物超导态的不均匀性,我们测量了La $_{2-x}$ Sr $_x$ CuO $_4$(LSCO)单晶在过掺杂区的磁化率$χ$.对于$x$ = 0.198和0.219,发现$χ$在1T中的温度依赖性表现出平台,即在SC状态中,$χ$在中等温度范围内几乎与温度无关。此外,在这些晶体中明显地出现了磁化曲线中的所谓第二峰。这些结果表明,异常增强的涡旋钉扎,并强烈建议发生$microscopic$相分离到SC和正常状态的区域中过掺杂的高$T_{\rm c}$铜酸盐。
Spectroscopic Evidence of Bilayer Splitting and Interlayer Pairing in an Iron Based Superconductor
在高温铜氧化物超导体中,CuO $_2$平面之间的层间耦合在决定超导电性方面起着重要的作用,正如临界温度(T $_C$)对一个结构单元中CuO $_2$平面数目的敏感依赖性所指示的。在$_2$超导体中,两个$_2$平面之间的相互作用导致能带分裂为两个费米面片(双层分裂),这两个费米面片具有明显的超导能隙。铁基超导体是由FeAs/FeSe层堆叠而成的,层间耦合是否会引起类似的能带分裂及其对超导电性的影响尚不清楚。本文报道了一种新发现的铁基超导体KCa $_2$ Fe $_4$ As $_4$ F $_2$(T $_C$ = 33.5K)的高分辨角分辨光电子能谱(ARPES)测量结果。首次观察到双层劈裂效应,在布里渊区中心周围产生了五个类空穴费米面片。能带结构计算再现所观察到的双层分裂,通过确定层间轨道间的相互作用,两个FeAs层内的一个FeAs块。在带中心附近的类空穴结构中,均存在费米面依赖的无节点超导能隙。提出了具有短程反铁磁涨落的能隙函数,当考虑层间配对时,能隙的对称性可以得到很好的理解。特别强的层间配对观察到的频带之一。我们的观测结果为理解铁基超导体的超导电性提供了层间耦合和层间配对的关键信息。
Unified order-disorder vortex phase transition in high-Tc superconductors
解释了在不同的高温$_{c}$超导体中测得的涡旋熔化和固-固转变线的多样性,假设由热诱导和无序诱导的波动驱动的统一的有序-无序相变。转变线的温度依赖性和无序相的性质(固体、液体或被钉扎液体)由这些波动的相对贡献和钉扎机制确定。通过改变钉扎机制和钉扎强度,可以获得单调和非单调过渡谱线,其类似于在Bi $_{2}$ Sr $_{2}$ CaCu $_{2}$ O $%_{8}$、YBa $_{2}$ Cu $_{3}$ O $_{7-δ}$、Nd $_{1.85}$ Ce $_{0.15}$ CuO $%_{4-δ}$、Bi $_{1.6}$ Pb $_{0.4}$ Sr $_{2}$ CaCu $_{2}$ O $_{8+δ}$和(La $% _{0.937}$ Sr $_{0.063}$)$_{2}$ CuO $_{4}$中测量的那些
Interlayer transport in high-$T_C$ cuprates is mediated by superconducting tunneling across the CuO$_2$ planes. For this reason, the terahertz frequency optical response is dominated by one or more Josephson plasma resonances and becomes highly nonlinear at fields for which the tunneling supercurrents approach their critical value, $I_C$. These large terahertz nonlinearities are in fact a hallmark of superconducting transport. Surprisingly, however, they have been documented in La$_{2-x}$Ba$_x$CuO$_4$ also above $T_C$ for doping values near $x=1/8$, and interpreted as an indication of superflu…
Anomalies in the ab-plane resistivity of strongly underdoped La_{2-x}Sr_{x}CuO_{4} single crystals: possible charge stripe ordering?
本文给出并讨论了小Sr含量(x=0.052-0.075)的La_{2-x} Sr_{x} CuO_{4}单晶的ab面电阻率的测量结果。通过使用AC Van der Pauw技术在4.2 K和300 K之间的温度范围内获得电阻率。当温度降低时,rho_{ab}(T)曲线显示出从线性行为到类似于双稳态行为的转变。与线性的偏离发生在掺杂依赖的温度T_{ch}。这种效应可以解释为由于预先存在的电荷条纹的渐进钉扎。在同样的框架下,超导样品的rho_{ab}(T)曲线在T_{c}正上方出现的异常尖峰,可以用从一个有序的近晶电子条纹相到一个更有序的近晶电子条纹相的转变来解释。
Magnetic-force-microscope study of interlayer "kinks" in individual vortices in underdoped cuprate YBa$_2$Cu$_3$O$_{6+x}$ superconductor
我们使用磁力显微镜的图像和操纵个别涡线线程单晶YBa $_2$铜$_3$ O $_{6.4}$,层状超导体。我们发现,当我们拉动一个固定涡的顶部时,它可能不会平滑地倾斜。有时,我们观察到一个漩涡分裂成离散的片段,可以描述为短叠的煎饼漩涡,类似于Benkraouda和Clem提出的“扭结”结构。定量分析给出了钉扎力和堆叠之间的耦合的估计。我们的测量突出了分层超导体中煎饼涡旋堆叠的离散性。
Hybridization of Bogoliubov-quasiparticles between adjacent CuO$_2$ layers in the triple-layer cuprate Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$ studied by ARPES
Current - voltage characteristics in magnetic field for layered superconductor with intrinsic pinning of Josephson vortices
M.N. Mikheev Institute of Metal Physics, Ural Branch, Russian Academy of Sciences(俄罗斯科学院乌拉尔分校 M.N. 米凯耶夫金属物理研究所);National Research Nuclear University MEPhI(国立核研究大学莫斯科工程物理学院)
We have previously shown for powders that Mo substitution into the CuO chains of YBa2Cu3O7 can create effective pinning centres which significantly increase the critical current density (j_c) in 7 T field by a factor of 4 and 10 at 50 and 60 K, respectively. The present work reports on the influence of the Mo substitution and high-pressure oxygen annealing on the pinning properties and critical currents of YBa_2Cu_{3-x}Mo_xO_{7-d} by comparing pure (x = 0, d > 0) and substituted (x = 0.03, d < 0) single crystals. Pinning properties have been investigated by measurements of magnetization loops …
Electron Dynamics in Nd$_{1.85}$Ce$_{.15}$CuO$_{4+δ}$: Evidence for the Pseudogap State and Unconventional c-axis Response
红外反射率的测量与光偏振沿a-和c-轴的超导和反铁磁相的电子掺杂的Nd $_{1.85}$ Ce $_{.15}$ CuO $_{4+δ}$。结果进行了比较,在空穴掺杂铜酸盐的电磁响应的特性。在CuO $_2$平面内,依赖于频率的散射速率1/ $τ(ω)$被压低到$\sim$ 650 cm $^{-1}$以下;这种行为是赝能隙态的标志。虽然在几个空穴掺杂的化合物的赝能隙和超导态的能量标度是相当接近的,我们能够表明,在Nd $_{1.85}$ Ce $_{.15}$ CuO $_{4+δ}$的两个规模相差超过一个数量级。面内电荷响应的另一个特征是在50-110 cm $^{-1}$处的电导率实部中的峰值$σ_1(ω)$,这与其中$σ_1(ω)$以$ω=0$为中心的Drude样响应形成鲜明对比。后者的效果是类似于在无序的空穴掺杂的铜氧化物中发现的,并在载流子本地化的上下文中进行了讨论。对c轴电导率的研究证明了层间超流体在一个非常宽的频率范围内聚集。Nd $_{1.85}$ Ce $_{.15}$ CuO $_{4+δ}$中的赝能隙态以及电荷动力学的其他特征的令人信服的证据表明,铜氧化物相图在电子和空穴掺杂方面具有全局相似性。
New surprises continue to be revealed about La$_2$CuO$_4$, the parent compound of the original cuprate superconductor. Here we present neutron scattering evidence that the structural symmetry is lower than commonly assumed. The static distortion results in anisotropic Cu-O bonds within the CuO$_2$ planes; such anisotropy is relevant to pinning charge stripes in hole-doped samples. Associated with the extra structural modulation is a soft phonon mode. If this phonon were to soften completely, the resulting change in CuO$_6$ octahedral tilts would lead to weak ferromagnetism. Hence, we suggest t…
Photoinduced Suppression of Superconductivity in Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$
高温超导体中的超导性是通过将电荷载流子引入到含有CuO $_2$平面的铜氧化物绝缘体中来实现的。这些CuO $_2$平面的扰动通过强烈影响电子环境来抑制超导性。本文利用Cu离子在CuO $_2$平面上的光致电子改性研究了Bi $_2$ Sr $_2$ Ca $_2$ Cu $_3$ O $_{10+δ}$中局域微扰的影响。这种方法已用于抑制超导转变温度T $_c$。我们表明,我们的结果光致抑制的超导性是一致的情况下,基于钉扎的波动条纹在Bi $_2$ Sr $_2$ Ca $_2$ Cu $_3$ O $_{10+δ}$。
Signature of T$_\textrm{c}$ above 111 K in Li-doped (Bi,Pb)-2223 superconductors: synergistic nature of hole concentration, coherence length and Josephson interlayer coupling
Electron-doped and hole-doped superconducting cuprates exhibit a symmetric phase diagram as a function of doping. This symmetry is however only approximate. Indeed, electron-doped cuprates become superconductors only after a specific annealing process: This annealing affects the oxygen content by only a tiny amount, but has a dramatic impact on the electronic properties of the sample. Here we report the occurrence of superconductivity in oxygen-deficient Nd$_{2-x}$Ce$_x$CuO$_4$ thin films grown in an oxygen-free environment, after annealing in pure argon flow. As verified by x-ray diffraction,…
Second magnetization peak (SMP) in hole-doped cuprates and iron pnictide superconductors has been widely explored. However, similar feature in the family of electron-doped cuprates is not common. Here, we report the vortex dynamics study in the single crystal of an electron-doped cuprate Pr$_{0.87}$LaCe$_{0.13}$CuO$_4$ superconductor using dc magnetization measurements. A SMP feature in the isothermal $M(H)$ was observed for $H$$\parallel$$ab$-planes. On the other hand, no such feature was observed for $H$$\parallel$$c$-axis in the crystal. Using magnetic relaxation data, a detailed analysis o…
Transport measurements provide important characterizations of the nature of stripe order in the cuprates. Initial studies of systems such as La(1.6-x)Nd(0.4)Sr(x)CuO(4) demonstrated the strong anisotropy between in-plane and c-axis resistivities, but also suggested that stripe order results in a tendency towards insulating behavior within the planes at low temperature. More recent work on La(2-x)Ba(x)CuO(4) with x=1/8 has revealed the occurrence of quasi-two-dimensional superconductivity that onsets with spin-stripe order. The suppression of three-dimensional superconductivity indicates a frus…
In underdoped cuprates, the interplay of the pseudogap, superconductivity, and charge and spin ordering can give rise to exotic quantum states, including the pair density wave (PDW), in which the superconducting (SC) order parameter is oscillatory in space. However, the evidence for a PDW state remains inconclusive and its broader relevance to cuprate physics is an open question. To test the interlayer frustration, the crucial component of the PDW picture, we performed transport measurements on La$_{1.7}$Eu$_{0.2}$Sr$_{0.1}$CuO$_{4}$ and La$_{1.48}$Nd$_{0.4}$Sr$_{0.12}$CuO$_{4}$, cuprates with…
Uniform mixing of antiferromagnetism and high-T_c superconductivity in multilayered copper oxides Ba_2Ca_{n-1}Cu_nO_{2n}F_2 with apical fluorines (n=2,3,4): Cu-NMR/NQR and F-NMR