Vortex Matter in the Presence of Magnetic Pinning Centra

Within the non-linear Ginzburg-Landau (GL) theory, we investigate the vortex structure of a thin type II superconductor with a ferromagnetic dot on top of it. Spontaneous creation of vortex-antivortex pairs as well as specific arrangements of vortices are found. We show that the equilibrium vortex phase diagram depends on the size of the magnetic dot and its magnetization, and we discuss the shell structure of the multivortex states with magic numbers which are size and magnetization dependent.     

Modeling of Nonlinear Surface Impedance of High-Tc Superconductors Using an Exponential Vortex Penetration Model

We have modeled surface impedance of YBa₂Cu₃O_7?δ thin films, using an exponential dependence on an applied rf magnetic field. For verification of the model we compared simulation results with experimental data of Nguyen et al. [2] and of Hein [14] at differing temperatures, frequencies and rf power levels. Obtained temperature dependence of the model fitting coefficients exhibited the same character in both cases.     

Modeling of Nonlinear Surface Impedance of High-Tc Superconductors Using an Exponential Vortex Penetration Model

We have modeled surface impedance of YBa₂Cu₃O_7– thin films, using an exponential dependence on an applied rf magnetic field. For verification of the model we compared simulation results with experimental data of Nguyen et al. [2] and of Hein [14] at differing temperatures, frequencies and rf power levels. Obtained temperature dependence of the model fitting coefficients exhibited the same character in both cases.     

Exotic Vortex Matter: Pancake Vortex Molecules and Fractional-Flux Molecules in Some Exotic and/or Two-Component Superconductors

The discovery of superconductivity in MgB₂ and, more recently, in iron pnictides, revived the interest in two-component and other exotic superconductors, including in the field of vortex matter, as was shown recently by the discovery of ??type 1.5?? superconductivity. However, even some ??older?? exotic cuprates grown by high-pressure techniques showed interesting anomalies related to the interplay between Josephson and magnetic coupling and/or two-gap superconductivity. Here, we will present two such examples of exotic vortex matter: magnetically-coupled pancake-vortex molecules in super-multilayered cuprates, and vortex molecules composed of fractional flux quanta glued by an interband phase difference soliton, and will discuss the major differences between MgB₂ and such multilayer cuprates in terms of the relative strength of the interband interaction and, respectively, in terms of the coherence and penetration lengths.     

The National High Magnetic Field Laboratory: Condensed Matter Science in Continuous Magnetic Fields

The National High Magnetic Field Laboratory (NHMFL) operates three facilities in support of magnet-related research. The main facilities are located at Florida State University, Tallahassee, Florida, the ultra-low-temperature high-magnetic-field facilities are located at the University of Florida, Gainesville, Florida, and the pulsed field facilities are located at the Los Alamos National Laboratory, Los Alamos, New Mexico. These facilities support a wide variety of magnet-related research capabilities that are open to all qualified users through a peer-reviewed proposal process. This paper summarizes the research capabilities at the DC facilities at the main facility of the NHMFL and the High B/T Facility at the University of Florida. A few select scientific achievements in the high field condensed matter sciences are presented to highlight the research capabilities available to all users. The NHMFL is supported by the United States National Science Foundation and the State of Florida.     

Superconducting Vortex Lattice Configurations on Periodic Potentials: Simulation and Experiment

Nb films have been fabricated on top of array of Ni nanodots. The array of periodic pinning potentials modifies the vortex lattice for specific values of the external applied magnetic field. By means of an implemented code developed from scratch, computer simulations based only on the vortex?Cvortex and the vortex?Cnanodot interactions provide the total interaction between vortices and pinning sites as well as the position of the vortices in the array unit cell. This simulation approach could be performed on square, rectangular or triangular arrays of nanodefects of different size.     

Magnetic Nondestructive Test for Resistance Spot Welds Using Magnetic Flux Penetration and Eddy Current Methods

Resistance spot welding technologies are widely used in industry. A highly reliable monitoring method is needed to effectively weld and create a robust structure. We developed a combined technique using magnetic flux penetration and an eddy current test (ECT). The magnetic measuring system consists of a pair of magnetic probes having an induction coil and detection coil, a lock-in amplifier, a current source, and a personal computer. The magnetic flux penetration through both surfaces at the weld was measured at low frequency. The ECT was performed at each surface with multiple frequencies. The magnetic flux penetration method showed good correlation with the destructive shear test because of the change in permeability due to the formation of the nugget. The ECT method reflected the depth profile of the nugget and was effective for determining a defective product.     

Statics and Dynamics of Vortex Matter with Competing Repulsive and Attractive Interactions

We numerically examine vortex matter with repulsive interactions at short range and attractive interactions at long range in the presence of periodic pinning arrays. Such competing vortex interactions are predicted to occur in multiband superconductors or type-I and type-II hybrid materials. For weak pinning, the vortices form cluster states, while for strong pinning, the vortices form uniform states in which flux is evenly distributed among the pinning sites. As a function of external drive, the weak pinning system exhibits clump depinning with no structure changes, while the strong pinning system depins into a disordered fluctuating state followed by a transition to a partially aligned stripe state. For weak pinning, there is a single peak in the differential conductivity, while for strong pinning there are two peaks, indicating that transport curves could be used to distinguish between vortex systems with purely repulsive interactions and those with additional long range attractive interactions.     

The Structure of a Quantized Vortex in a Bose-Einstein Condensate

The structure of a quantized vortex in a Bose-Einstein Condensate is investigated using the projection method developed by Peierls, Yoccoz, and Thouless. This method was invented to describe the collective motion of a many-body system beyond the mean-field approximation. The quantum fluctuation has been properly built into the variational wave function, and a vortex is described by a linear combination of Feynman wave functions weighted by a Gaussian distribution in their center positions. In contrast to the solution of the Gross-Pitaevskii equation, the particle density is finite at the vortex axis and the vorticity is distributed in the core region.     

Critical Radius and Magnetic Field for Vortex Nucleation on a Superconducting Spherical Surface

Spherical, two-dimensional electron systems are realized in nanoshells and multielectron bubbles in helium. In this contribution, we investigate the superconducting state of such shells using a variational Ginzburg-Landau formulation. A phase diagram as a function of the sphere radius and the magnetic field is derived, and we calculate a critical radius below which vortices cannot be nucleated on the superconducting spherical surface.     

气辅成型过程气体穿透行为的MPI三维模拟及实验

采用MPI/GAS-3D模块分析了不同延迟时间和气体压力条件下的气体穿透效果,并与该工艺条件下实验测定的高密度聚乙烯(HDPE)气体辅助注射成型(GAIM)制品的气体穿透长度(GPL)及残余壁厚(RWT)进行比较,探讨了气辅成型中延迟时间和气体压力等关键工艺参数对制品气体穿透长度和残余壁厚的影响,利用实验数据分析了气体穿透长度与残余壁厚之间的定性关系。     

The Peculiarities of Americium Electronic Structure and Magnetic Susceptibility

By implementing a self-consistent procedure that combines the calculations of electronic spectrum within LDA+U+SO approximation with a generalized spin-fluctuation s(p)df-model, we have calculated the densities of states and temperature dependence of magnetic susceptibility of Americium. It was revealed that in the vicinity of the Fermi energy the densities of states of Am d-electrons become comparable to its f-electron densities of states that leads to that both bands make comparable contributions to the spin magnetic susceptibility. It is shown that the unusual transition from Curie-like to Pauli-like magnetic susceptibility, which is observed in Am, is caused by coexistence in Am of electronic states of two types—the localized, responsible for the formation of Curie-like susceptibility and the itinerant, which lead to temperature-independent magnetic susceptibility.     

基于MEMS存储器中二维驱动机构数值模型分析与实验

分析了MEMs数据存储器机构中柔性弹簧的线性大位移驱动特性,提出了一种等效数值模型,并利用该模型等效替换数据存储器驱动机构的关键部位,保留了MEMS数据存储器驱动机构的实际工作特性,并在此基础上将驱动机构转换成质量块和弹簧结构两种单元形式,解决了驱动机构中相对小尺寸有限元建模的问题,大大减少了单元数量．通过设计实验系统进行对比验证,驱动仿真分析结果与实验结果具有良好的吻合性,验证了该等效过程及模型的正确性．为MEMS数据存储器驱动机构的开发提供了理论设计和实验参考．     

Results and Prospects for the Cryogenic Dark Matter Search (CDMS) Experiment

The Cryogenic Dark Matter Search (CDMS) experiment, located at the Soudan underground mine, operated 30 low-temperature Ge and Si detectors for several years to search for Weakly Interacting Massive dark matter Particles (WIMPs). Due to their excellent background discrimination power and low energy threshold, our detectors have provided world-leading sensitivity for WIMP-nucleon interactions for most of the past decade over a large WIMP mass range. The final exposure of our CDMS?II detectors yielded two candidate events, with an expected background of 0.9 ± 0.2 events, and this result was published in March 2010 in Science. A reanalysis of 8 Ge detectors with a lowered, 2 keV recoil energy threshold, provided increased sensitivity to interactions from WIMPs with masses below ?10 GeV/c² and excluded possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments. The CDMS collaboration is moving forward with the SuperCDMS experiments at Soudan and SNOLAB with the goal of probing the zeptobarn scale and beyond over the next decade. To achieve this goal, a new generation of larger mass detectors with interleaved geometry for the phonon and ionization readout has been developed.     

Magnetic Field Analysis and Structure Design of a New Magnetic Wheel for Wall-Climbing Robot

Journal of Superconductivity and Novel Magnetism - According to the working requirements of the wall-climbing robot, a wall-climbing method using a permanent magnet wheel to realize wall surface...     

存在油墨渗透印刷品色彩预测Kubelka-Munk理论模型

油墨与纸张均是均匀介质,将印刷品分为油墨层、油墨渗透层和纸张层,并分别建立模型,在漫反射光的照射下,利用Kubelka-Munk理论和多重内反射的Sanderson修正,以及以点扩散函数为基础的网点扩大的修正,来建立新的半色调印刷品色彩预测模型.在此基础上,将模型推广到双面半色调印刷的情形.新模型也可为印刷品的呈色规律分析与印刷品在线检测提供理论依据.     

Electron-optical Observation of Magnetic Flux Quanta in Superconductors by Decoration and Vortex Microscopy

The stray field modulation of magnetic flux in superconductors can be converted into an optical or electron optical contrast by various decoration techniques, which are reviewed. Thin films decorated in this way are analysed in a transmission, scanning, or scanning transmission electron microscope and permit one to study the configuration of the magnetic flux relative to the crystalline structure. Results of electron interferometer experiments on the flux quantization in small superconducting hollow cylinders, on the motion of single flux quanta, and on their pinning forces at grain boundaries, will be surveyed.