We report on the design and operation of a transport critical-current measurement option for superconductors based on the widely used Physical Property Measurement System from Quantum Design. The system is capable of supplying transport currents up to 30 A while maintaining a sample temperature of 2.0 +/- 0.1 K, and currents up to 200 A at higher sample temperatures.
The interplay between the thermal transport property and the topological aspect is investigated in a spin-triplet chiral p-wave superconductor Sr2RuO4 with the strong two-dimensionality. We show the thermal Hall conductivity is well described by the temperature linear term and the exponential term in the low temperature region. While the former term is proportional to the so-called Chern number directly, the latter is associated with the superconducting gap amplitude of the gamma band. We also demonstrate that the coefficient of the exponential term changes the sign around Lifshitz transition.…
Whereas there are two critical fields that are H$_{c1}$ and H$_{c2}$ in the ideal type II superconductor, there is another critical field H$_{c1}'$ defined as the field showing the maximum diamagnetic property in the real type II superconductor. We would present that H$_{c1}'$ is able to be proved theoretically and experimentally. We have derived an equation based on flux-pinning effect of volume defects. MgB$_2$ bulks which were synthesized by Mg and B are similar to this model. The number of quantum fluxes pinned at a defect of radius r, a pinning penetration depth, magnetic flux penetration…
Magnetic response is a fundamental property of superconducting materials, which helps to distinguish two superconductivity types: the ideally diamagnetic type I and type II, which can develop the mixed state with Abrikosov vortices. We demonstrate that multi-band superconductors with one shallow band, that have recently attracted much attention for their high critical temperatures and unusual properties, often stay apart of this simple classification. In a wide range of microscopic parameters such systems fall into the inter-type or transitional interval in between the standard types and displ…
本文回顾了俄罗斯科学院喀山物理技术研究所（E. G. Kharakhash'yan）与喀山国立大学（B. I. Kochelaev）和俄罗斯科学院物理问题研究所（N. E. Alekseevskii）提出。我们首次观察到了第二类超导体中杂质的电子顺磁共振;发现了由于超导关联而引起的磁性杂质之间的长程交换相互作用的迹象;观察到了超导状态下杂质的磁有序;最后，我们发现了1：2：3高$T_c$超导体的非均匀性的第一个证据，这是它的自然属性之一
Increasing and improving the critical transition temperature (Tc), current density (Jc) and Meissner effect (Hc) of conventional superconductors are the most important problems in superconductivity research, but progress has been slow for many years. In this study, by introducing the p-n junction electroluminescent inhomogeneous phase with red wavelength to realize energy injection, we found the improved property of smart meta-superconductors MgB2, the critical transition temperature Tc increases by 0.8K, the current density Jc increases by 37%, and the diamagnetism of Meissner effect Hc also …
Analysis of current-voltage characteristics of two-dimensional superconductors: finite-size scaling behavior in the vicinity of the Kosterlitz Thouless transition
有人建议[Pierson et al.，Phys.Rev.B60，1309（1999）; Ammirata等人，Physica C 313，225（1999）]指出，对于2D超导体，存在动态临界指数z \approx 5.6的相变。我们对2D RSJ模型进行了模拟，并将结果与Repaci等人获得的一个YBCO样品的实验数据[Phys. Rev. B 54，R9674（1996）]进行了比较。然后，我们使用与Pierson等人不同的分析动态缩放的方法，并得出结论，无论是模拟和实验是一致的，与传统的Kosterlitz无（KT）过渡的热力学极限，其中z=2。然而，对于有限系统，我们发现在模拟和实验中，由有限尺寸引起的电流-电压（IV）特性的变化显示出指数α \approx 1/6的标度特性，似乎表明在z=1/alpha的温度下电阻消失。指出Pierson等人提出的动态临界指数对应于指数1/α。需要强调的是，这种比例特性并不代表任何真正的相变，因为实际上电阻仅在零温度下才消失。然而，观察到的与α \approx 1/6相关的标度行为似乎是有限尺寸引起的KT转变周围IV特性变化的常见且有趣的特征。
Doping dependence of Normal-state Property in the Iron-based Oxypnictide Superconductors LaFeAsO1-y probed by 57Fe-NMR and 75As-NMR/NQR
本文报道了贫氧铁基氧氮族化合物超导体LaFeAsO_{1-y} $. A microscopic phase separation between superconducting domains and magnetic domains is shown to take place in the underdoped sample, indicating a local inhomogeneity in association with the density distribution of oxygen deficiencies. As a result, 1/T_1T in the normal state of the superconducting domain decreases significantly upon cooling at both the Fe and As sites regardless of the electron-doping level in LaFeAsO_{1-y}. On the basis of this result, we claim that $ 1/T_1 T $ is not always enhanced by antiferromagnetic fluctuations close to an antiferromagn…
Recent excitement in observation of non-reciprocal critical current (NRC) is motivated by a suggestion that "superconducting diode effect" may be an intrinsic property of non-centrosymmetric superconductors with strong spin-orbit interactions[1]. Theoretically it has been understood that linear in the Cooper pair momentum terms, caused by the Rashba spin-orbit and Zeeman interactions or, more generally, any symmetry-allowed Lifshitz invariants[2] in uniform singlet superconductors, do not contribute to the supercurrent, although the role of higher-order terms remains unclear[3, 4]. In this wor…
Best practices for a proper evaluation and conversion of physical property equations in superconductors: the examples of WHH formulation, Bean model and other cases of interest
National High Magnetic Field Laboratory, Florida State University（国家强磁场实验室，佛罗里达州立大学）；M.N. Miheev Institute of Metal Physics, Ural Branch, Russian Academy of Sciences（俄罗斯科学院乌拉尔分支米涅耶夫金属物理研究所）；NANOTECH Centre, Ural Federal University（乌拉尔联邦大学纳米技术中心）；CNR-SPIN, Physics Department（意大利国家研究委员会自旋物理研究所）；Institute for Technical Physics, Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院技术物理研究所）；Robinson Research Institute, Victoria University of Wellington（惠灵顿维多利亚大学罗宾逊研究院）；FAMU-FSU College of Engineering, Florida State University（佛罗里达州立大学 FAMU-FSU 工程学院）
We report on orbital-dependent quasiparticle dynamics in EuFe$_2$As$_2$, a parent compound of Fe-based superconductors and a novel way to experimentally identify this behavior, using time- and angle-resolved photoelectron spectroscopy across the spin density wave transition. We observe two different relaxation time scales for photo-excited d$_x$$_z$/d$_y$$_z$ and d$_x$$_y$ electrons. While d$_x$$_z$/d$_y$$_z$ electrons relax faster through the electron-electron scattering channel, showing an itinerant character, d$_x$$_y$ electrons form a quasi-equilibrium state with the lattice due to their l…
Universal scaling behaviour in superconductors has significantly elucidated fluctuation and phase transition phenomena in these materials. However, universal behaviour for the most practical property, the critical current, was not contemplated because prevailing models invoke nucleation and migration of flux vortices. Such migration depends critically on pinning, and the detailed microstructure naturally differs from one material to another, even within a single material. Through microstructural engineering there have been ongoing improvements in the field-dependent critical current, thus illu…
In this work we explore the chemical-property phase diagram of the AV$_3$Sb$_5$ family through A-site alloying. We demonstrate full miscibility of the alkali-site, highlighting that the three parent compounds are the terminal ends of a single solid-solution. Using both polycrystalline and single crystal methods, we map the dependence of the two primary electronic instabilities: (1) the onset of charge density wave (CDW) order ($T_\text{CDW}$) and (2) the onset of superconductivity ($T_\text{c}$) with alkali-site composition. We show continuous trends in both $T_\text{CDW}$ and $T_\text{c}$, in…
We propose a targeted attack on making the Fe-based superconductor (FBS) AEFe2As2 (122) (AE = alkaline earth, here Ba or Sr) into a much cheaper, higher stability margin, round, twisted and effectively isotropic multifilament conductor suitable for 16-20 T dipole magnet construction. This white paper urges to greatly accelerate progress by providing a fundamental understanding of what controls the transport critical current density, Jc, of 122 polycrystals and then in the wire forms. High grain-to-grain Jc is the one key property not yet fully demonstrated in this new superconductor and this i…
A New Physical Model of Pairing Mechanism in Superconductors: Could the Electron itself be treated as a Composite Particle to Achieve Room Temperature Superconductor?
We demonstrate that current-current correlations (in particular the shot noise), can be used to study the intrinsic superconductivity in a slightly doped Weyl semi-metal. The systems studied is an N-WS tunneling junction where the left electrode is a normal metal while the right electrode is a Weyl superconductor (WS). The superconductivity supports surface state with crossed flat bands thereby impact the low energy spectrum. This spectrum displays a modified density of states in the gap region that strongly affects transport characteristics of the N-WS junction. The Fano factor is calculated …
In a small subset of type II superconductor films, the critical current is determined by a weakened Bean-Livingston barrier posed by the film surfaces to vortex penetration into the sample. A film property thus depends sensitively on the surface or interface to an adjacent material. We theoretically investigate the dependence of vortex barrier and critical current in such films on the Rashba spin-orbit coupling at their interfaces with adjacent materials. Considering an interface with a magnetic insulator, we find the spontaneous supercurrent resulting from the exchange field and interfacial s…
