Current and Temperature Dependent Matching Fields in Nb Film of Rectangular Array of Holes

Nanoengineered periodic array of holes on superconducting thin films have a great interest due to their excellence for the studies of the vortex pinning mechanisms in the type-II superconductors. Rectangular array of holes has been fabricated over a microbridge of Nb superconducting thin film by e-beam lithography. Rectangular array of holes have two type of scenario, at low magnetic fields matching effects are sharp and narrow while at high fields wide and shallower. In this work, we study the matching pinning effect by the artificial hole array in superconducting Nb thin films. We observed that as the inter distance between holes is decreased; the sharp matching effects become dominant and vice versa.     

Stability of a Liquid Film on a Surface with Periodic Array of Gas-filled Grooves

We develop a linear stability theory for a thin liquid film on a structured solid surface with periodic grooves filled by a gas. The main mechanism driving the instability is due to the London-van der Waals disjoining pressure. The grooves are shown to have a destabilizing effect on the film. The results of linear stability analysis are compared with numerical simulations based on the strongly nonlinear equation for film thickness.     

基于周期势函数的自适应二阶欠阻尼随机共振信号增强方法

针对滚动轴承微弱故障振动信号在噪声环境下故障特征难以提取的问题,提出一种基于周期势函数的自适应二阶欠阻尼随机共振信号增强方法。采用粒子群算法对系统参数和阻尼系数的自适应匹配,实现对多个拟增强频段的随机共振,更加适用于工程实际中多故障信号提取。数据库考题检验和工程实验验证表明:1)该方法明显提高了输出信噪比,故障特征频率处主峰突出,边带干扰少,方便故障的机器判读,误判率低;2)随着噪声强度的增加,虽然输出信噪比有所降低,但该方法的检测效果仍优于基于周期势函数的自适应一阶随机共振方法的检测效果;3)该方法对噪声的适应性更强,在噪声环境下对于微弱故障信号的提取有着明显优势。     

Coherence Between Superconducting Edge States in Superconducting Periodic Arrays of Artificial Defects

The transition line of superconducting arrays of holes exhibits a rich field structure due to the interference of superconducting states nucleated at the holes edges. We studied by means of resistance measurements their effect on the T* _c (H) line as a function of transverse magnetic field using regular arrays of nanofabricated micron size holes. The arrays transition fields are higher than for the bulk. Moreover we found a nontrivial field modulation of the T* _c (H) line with an inversion, with increasing field, of the modulation concavity which we assigned to a crossover from a collective to an isolated edge state regime. The high field regime is well described by the nucleation at a single hole in an infinite film. The modulation at low fields was found to be dominated by the interference of neighbor edge states when the inter-hole distance w becomes comparable to the coherence length (T* _c ). A comparison between arrays of different hole shape shows the influence of geometry on the type of interaction established, which can described either as a superconducting wire network or as a weak link array.     

基于频率调制随机共振的弱周期信号检测

将调制技术与随机共振原理相结合,提出用频率调制随机共振的方法,实现在大参数情况下从强噪声中检测微弱周期信号,并对随机共振技术运用于强噪声背景下的弱信号检测进行研究。分析调频信号的频谱,发现其含有的低频信号通过双稳系统易产生随机共振,数值分析及仿真结果表明该方法能使微弱的故障信号特征突出、明显而易于捕捉。     

Superconducting and Structural Properties of Nb/PdNi/Nb Trilayers

The superconducting and structural properties of S/F/S (Superconductor/Ferromagnet/Superconductor) heterostructures have been studied by means of microwave measurements (1–20 GHz) and x-ray absorption fine structure (XAFS) spectroscopy. Nb/PdNi/Nb trilayers have been studied as a function of F layer thickness. With respect to pure Nb, XAFS analysis shows that the heterostructures exhibit larger structural disorder in the S layers. Microwave measurements show evidence for a progressively weaker vortex pinning with increasing F thickness. However, no clear correlation is found with the local disorder in Nb: the weakest pinning is not in the most disordered trilayer. Therefore, the structural disorder in the superconducting material cannot explain on its own the changes in vortex pinning. We argue that the F layer acts on the superconducting state itself. We propose possible explanations for the observed behavior.     

Anderson Localization in Nb/Al Superconducting Bilayers

We have measured the temperature dependence of resistivity in relatively thick Nb/Al bilayers fabricated at room temperature, observing the decrease of for increasing T typical of Anderson localization in disordered systems. We report the experimental conditions which determine this behavior and compare it to theoretical models for localization in 3D systems.     

薄膜制备中的微蚀孔问题

研究了自终止腐蚀停法制备浓硼重掺杂硅薄膜的腐蚀孔问题．许多MEMS结构需要进行2次或2次以上的深刻蚀,有些需要在多次深刻蚀后释放超薄的悬空薄膜结构,这时薄膜表面极易出现微小的腐蚀孔．分析可知,微蚀孔并不完全在第2次腐蚀的过程中形成,而是从第1次深腐蚀过程中对掩膜层的钻蚀开始的．对掩膜层的钻蚀,导致硅表面出现轻微腐蚀,形成细小的凹坑,并在浓硼扩散和第2次深腐蚀中被放大,最终在成膜过程中形成小孔．分析了微蚀孔的成因,提出了工艺上的解决方法,形成了一套重复性好的成膜工艺．     

Superconducting gap in Nb seen by point contact spectroscopy

The nonlinear current voltage characteristics of a point contact convey information about various excitations in the metal. We have made a point contact study on a superconductor to see the band gap and on a normal metal to see the transport characteristics.     

FeSe超导薄膜的研究进展

FeSe及其相关化合物的高温超导性引起了凝聚态物理研究人员的广泛关注。在所有铁基超导体中,FeSe的成分和晶体结构最为简单,只存在铁基超导体最基本的结构单元FeSe层。FeSe超导体具有特殊的电子结构和物理特性,是铁基高温超导机制研究的理想平台。2012年,薛其坤组在SrTiO_3(STO)衬底表面采用分子束外延(MBE)法生长了单层FeSe薄膜,发现该体系的超导转变温度(TC)有接近80K的迹象,引起人们的广泛关注。先简要地介绍了FeSe晶体,FeSe/石墨烯薄膜的超导特性,再详细介绍了FeSe/SrTiO_3高温超导薄膜的输运性质、超导特性、电子结构以及可能影响单层FeSe/SrTiO_3薄膜高温超导的几个因素。     

具有随机参数的线性振荡器的随机共振

研究了噪声作用下的具有随机参数的过阻尼线性振荡器的随机共振现象.基于线性系统理论,得到了系统输出幅度增益的精确表达式.研究表明,输出幅度的增益是噪声强度和激励信号频率的非单调函数.而且,适当的噪声强度和振荡器参数可以使有噪声情况下的输出幅度增益大于无噪声时的输出幅度增益.讨论了噪声的强度和振荡器参数对输出幅度增益的影响.     

Anisotropy in the Transport Properties of Type II Superconducting Films with Periodic Pinning

Using numerical simulations, we analyze the anisotropy effects in the critical currents and dynamical properties of vortices in a thin superconducting film submitted to hexagonal and Kagomé periodical pinning arrays. The calculations are performed at zero temperature, for transport currents parallel and perpendicular to the main axis of the lattice, and parallel to the diagonal axis of the rhombic unit cell. We show that the critical currents and dynamic properties are anisotropic for both pinning arrays and all directions of the transport current. The anisotropic effects are more significant just above the critical current and disappear with higher values of current and both pinning arrays. The dynamical phases for each case and a wide range of transport forces are analyzed.     

Periodic System of Closely Located Holes in a Quasiorthotropic Plane

Materials Science - We study a plane periodic problem of the theory of elasticity for a quasiorthotropic plane with an infinite series of closely located curvilinear holes by the method of singular...     

Heat Treatment of Two-Turn Nb3Sn Superconducting Coil

A heat treatment system was built at High Magnetic Field Laboratory, Chinese Academy of Sciences (CHMFL) for the heat treatment of large-scale Nb₃Sn superconducting coils and conductors. In order to evaluate the manufacturing technique of the joints for the Nb₃Sn CICC, a two-turn Nb₃Sn superconducting coil with two superconducting joints had been developed. A two-turn coil together with several Nb₃Sn witness samples was heat-treated. Experimental and finite elemental analysis was also discussed. The results of the measurements met the requirements of the magnet design.     

参数扰动的RLC低通滤波器的随机共振

研究了RLC低通滤波器在电导受到非对称双值色噪声扰动时的随机共振现象.利用随机平均法和Shapiro-Loginov公式,得到了平均输出幅度增益的精确表达式.分析表明,在欠阻尼、临界阻尼和过阻尼RLC低通滤波器中,平均输出幅度增益对电导噪声的非对称性、相关时间、强度和信号频率都存在非单调依赖关系.适当的噪声和系统参数条件可以使有噪声时系统的平均输出幅度增益大于没有噪声时系统的平均输出幅度增益.噪声可以提高滤波器对高频信号的衰减率.恰当的条件可以获得平均输出幅度增益的最大值.     

参数扰动的RLC低通滤波器的随机共振

研究了RLC低通滤波器在电导受到非对称双值色噪声扰动时的随机共振现象．利用随机平均法和Shapiro—Loginov公式,得到了平均输出幅度增益的精确表达式．分析表明,在欠阻尼、临界阻尼和过阻尼RLC低通滤波器中,平均输出幅度增益对电导噪声的非对称性、相关时间、强度和信号频率都存在非单调依赖关系．适当的噪声和系统参数条件可以使有噪声时系统的平均输出幅度增益大于没有噪声时系统的平均输出幅度增益．噪声可以提高滤波器对高频信号的衰减率．恰当的条件可以获得平均输出幅度增益的最大值．     

Boson Gas in a Periodic Array of Tubes

We report the thermodynamic properties of an ideal boson gas confined in an infinite periodic array of channels modeled by two, mutually perpendicular, Kronig-Penney delta-potentials. The particle’s motion is hindered in the x–y directions, allowing tunneling of particles through the walls, while no confinement along the z direction is considered. It is shown that there exists a finite Bose-Einstein condensation (BEC) critical temperature T _c that decreases monotonically from the 3D ideal boson gas (IBG) value T ₀ as the strength of confinement P ₀ is increased while keeping the channel’s cross section, a _x a _y constant. In contrast, T _c is a non-monotonic function of the cross-section area for fixed P ₀. In addition to the BEC cusp, the specific heat exhibits a set of maxima and minima. The minimum located at the highest temperature is a clear signal of the confinement effect which occurs when the boson wavelength is twice the cross-section side size. This confinement is amplified when the wall strength is increased until a dimensional crossover from 3D to 1D is produced. Some of these features in the specific heat obtained from this simple model can be related, qualitatively, to at least two different experimental situations: ⁴He adsorbed within the interstitial channels of a bundle of carbon nanotubes and superconductor-multistrand-wires Nb₃Sn.     

Magnetic Normal Modes in Squared Antidot Array With Circular Holes: A Combined Brillouin Light Scattering and Broadband Ferromagnetic Resonance Study

We present a combined experimental investigation of magnetic normal modes in an antidot lattice using both Brillouin light scattering and broadband ferromagnetic resonance. It was fabricated on a silicon substrate using optical ultraviolet lithography. The sample consisted of a 30-nm-thick ${rm Ni}_{80}{rm Fe}_{20}$ squared antidot array with circular holes whose diameter and edge-to-edge spacing are 250 and 150 nm, respectively. Experiments were performed as a function of the applied magnetic field $mu_{0}{rm H}_{rm ext}$ in the range from $-$100 to 100 mT, with ${rm H}_{rm ext}$ applied along both the square lattice axis and its diagonal. Several peaks were observed in both the Brillouin light scattering and ferromagnetic resonance spectra, and their evolution with the intensity and the direction of the applied field ${rm H}_{rm ext}$ was measured. Micromagnetic simulations enabled us to identify the modes in terms of their symmetry obtaining a good quantitative agreement with the measured frequencies. In addition, we show how the inhomogeneity of the internal field affected the properties of the magnetic eigenmodes and their localization in different regions of the antidot lattice.