Lateral magnetic stiffness under different parameters in a high-temperature superconductor levitation system

Magnetic stiffness determines the stability of a high-temperature superconductor(HTS) magnetic levitation system.The quantitative properties of the physical and geometrical parameters that affect the stiffness of HTS levitation systems should be identified for improving the stiffness by some effective methods. The magnetic stiffness is directly related to the first-order derivative of the magnetic force with respect to the corresponding displacement, which indicates that the effects of the parameters on the stiffness should be different from the relationships between the forces and the same parameters.In this paper, we study the influences of some physical and geometrical parameters, including the strength of the external magnetic field(B0) produced by a rectangular permanent magnet(PM), critical current density(Jc), the PM-to-HTS area ratio(α), and thickness ratio(β), on the lateral stiffness by using a numerical approach under zero-field cooling(ZFC)and field cooling(FC) conditions. In the first and second passes of the PM, the lateral stiffness at most of lateral positions essentially increases with B0 increasing and decreases with β increasing in ZFC and FC. The largest lateral stiffness at every lateral position is almost produced by the minimum value of Jc, which is obviously different from the lateral force–Jc relation. The α-dependent lateral stiffness changes with some parameters, which include the cooling conditions of the bulk HTS, lateral displacement, and movement history of the PM. These findings can provide some suggestions for improving the lateral stiffness of the HTS levitation system.     

基于LabVIEW的高温超导材料特性测试实验

高温超导体临界特性的测量是近代物理实验中最为经典的实验之一,本文通过使用GM制冷机,利用Lab-VIEW虚拟仪器软件和高性能采集卡,改进了传统的测量高温超导材料临界特性的实验装置.本测试系统不仅可以测量高温超导体在不同温度下的临界电流,还可以测量其失超传播特性.该实验对于学生了解超导体特性和培养严谨的科学作风十分有益.     

Levitation of a rapidly oscillating magnetic dipole above a metallic sheet

We show that such a magnetic dipole suspended at a height h above a conducting sheet experiences a lift force proportional to $1/h^2$. This represents an order of magnitude improvement over the $1/h^4$ lift obtained in the quasistatic limit.     

组合振子天线磁偶特性实验研究

通过对组合振子的实验研究,验证了磁偶极子回路所具有的优势:能够极大地改善天线低频传输以及辐射特性,具有明显的低频补偿能力。此外,通过设置磁偶回路周长比,比较了不同磁偶回路状态下的天线特性,发现双磁偶回路对于低频特性的改善要优于单磁偶回路,后者的优势主要体现在高频。根据这一现象,采用单磁偶回路结构设计工作频带为300MHz~5GHz组合振子接收天线。     

组合振子天线磁偶特性实验研究

通过对组合振子的实验研究,验证了磁偶极子回路所具有的优势：能够极大地改善天线低频传输以及辐射特性,具有明显的低频补偿能力。此外,通过设置磁偶回路周长比,比较了不同磁偶回路状态下的天线特性,发现双磁偶回路对于低频特性的改善要优于单磁偶回路,后者的优势主要体现在高频。根据这一现象,采用单磁偶回路结构设计工作频带为300 MHz~5 GHz组合振子接收天线。     

磁偶极和电四极在磁各向异性介质中的辐射功率

在经典电动力学的框架下,研究了磁各向异性介质中的电磁辐射问题,得到了磁偶极和电四极在磁各向异性介质中的辐射功率表达式.进一步地,通过把各向同性介质中的μrii代入所得辐射功率表达式,得到了与文献相符合的结果,验证了所得结果的正确性.研究结果表明磁偶极和电四极在磁各向异性介质中的辐射功率大小与磁各向异性介质的μrii大小有关,对判断磁偶极和电四极在磁各向异性介质中的辐射效果有较大的帮助.     

Helmet-size vessels of high-Tc oxide superconductor for magnetic shield

We have developed a very large magnetic shielding vessel made from high-T_c Bi-Pb-Sr-Ca-Cu-O superconductor and have experimentally confirmed that this vessel can reduce a weak magnetic field to -100 dB or 1/10⁵. The size of this vessel is 32 cm in diameter, 64 cm in depth and 2.5 cm in thickness. The shielding effect of the vessel does not decrease even at a low frequency like 0.2 Hz. The high attenuation ratio in the low frequency range indicates that magnetic shielding using a high-T_c superconductor is promising for neuromagnetic measurements with SQUID.     

高温超导体的磁激发:探寻不同体系铜氧化合物的共同特征

文章回顾了中子散射在高温超导铜氧化合物磁激发研究中的最新进展．自从铜氧化合物在20年前被发现以后，理解它们超导电性的微观来源一直是凝聚态物理中的核心课题．在传统超导体中，使得电子成对形成超导态的相互作用是以晶格振动（声子）为媒介的、而对于铜氧化合物的超导机理，人们通常认为磁激发可能起到根本的作用，因为超导电性是在可移动的“电子”或“空穴”掺杂到反铁磁母体化合物之后才发生的．文章总结了过去20年来利用非弹性中子散射研究磁激发的关键结果和现状，并指出了将来可能的研究方向．     

运动介质的电偶极矩与磁矩

在推导出介质的极化强度与磁化强度的坐标变换公式的基础上,分析导出了运动介质的电偶极矩与磁矩.     

电子型FeSe基高温超导体的磁通束缚态与Majorana零能模

作为凝聚态物理中一类新奇准粒子态,Majorana零能模(Majorana zero mode)由于可用来实现拓扑量子计算而成为当前的研究热点.理论预言,Majorana零能模可作为特殊的束缚态出现在一些拓扑超导体的磁通涡旋中.但实际超导体磁通中还可能存在其他低能束缚态或杂质态,这给Majorana零能模的辨别和具体应用带来了困难.目前实验上寻找合适的拓扑超导体系、分辨出清晰的Majorana零能模仍然是十分迫切的.本文主要介绍最近利用高能量分辨的扫描隧道显微镜,对电子掺杂铁硒类超导体(Li,Fe)OHFeSe和单层FeSe/SrTiO3磁通态进行的研究.实验上在前者的自由磁通中观测到清晰的零能模,并进一步测量到Majorana零能模的重要特征—量子化电导.而在后者磁通中只发现常规Caroli-de Gennes-Matricon(CdGM)束缚态,反映出s波对称性的特征.这系列实验既为Majorana零能模物性的进一步研究提供了合适平台,也为澄清铁基超导体中拓扑超导电性的来源提供了线索.     

Lifshitz时空s波超导模型的关联长度和穿透深度

在D=d+2维各向异性的Lifshitz黑洞时空背景中, 在探子极限下, 用解析方法研究了临界温度附近引力系统的微扰, 计算出超导的关联长度ξα(1/T_c)(1-(T/T_c)^-1/2, 这与平均场论的结果一致. 进一步, 考虑在该系统中加一个均匀外磁场, 计算出穿透深度λα(T_c-T)^-1/2, 该结果与Ginzburg-Landau理论相符.     

钕铁硼在高温超导磁悬浮技术实验中的应用

将新材料钕铁硼作为磁导轨引入到高温超导磁悬浮技术实验中,介绍了高温超导悬浮技术实验的基本原理、仪器及钕铁硼对实验的改进.     

NdFeB永磁体下YBaCuO块材在交流磁扰动中的悬浮力磁滞特性

研究了交流磁扰动对高温超导块材和永磁体之间悬浮力的影响。实验分析了在零场冷(ZFC)条件下,不同频率的交流磁场扰动下的悬浮力曲线;另外还研究了交流磁扰动在永磁体下降和上升过程中对悬浮力的影响,发现上升过程中悬浮力受交流磁场影响较大,而在下降过程中影响则较为不明显,同时随着交流磁场幅值的增大,悬浮力的滞回曲线逐渐加宽。说明交流磁场导致了超导块磁滞损耗的增加,对超导磁浮特性的研究具有理论意义。     

Polarization control over electric and magnetic dipole resonances of dielectric nanoparticles on metallic films

We reveal unusually strong polarization sensitivity of electric and magnetic dipole resonances of high‐index dielectric nanoparticles placed on a metallic film. By employing dark‐field spectroscopy, we observe the polarization‐controlled transformation from high‐Q magnetic‐dipole scattering to broadband suppression of scattering associated with the electric dipole mode, and show numerically that it is accompanied by a strong enhancement of the respective fields by the nanoparticle. Our experimental data for silicon nanospheres are in an excellent agreement with both analytical calculations based on Green's function approach and the full‐wave numerical simulations. Our findings further substantiate dielectric nanoparticles as strong candidates for many applications in enhanced sensing, spectroscopy and nonlinear processes at the nanoscale.

     

钫原子磁偶极超精细结构常数及其同位素的磁偶极矩的理论计算

应用基于B样条基组的相对论耦合簇理论方法,计算了~(212)Fr原子的n S (n=7—12), n P (n=7—12)和n D (n=6—11)态的磁偶极超精细结构常数.与精确实验值的比较说明这套理论方法能精确计算出磁偶极超精细结构常数,其中7P态的磁偶极超精细常数的理论值与实验值之间的差异小于1%.在忽略场移效应对Fr原子7P态超精细结构常数的影响下,通过结合实验值进一步定出了~(207-213,220-228)Fr核磁偶极矩μ,这些值与已有的测量值具有非常好的一致性.本文报道了12S, n P (n=9—12)和n D (n=10—11)态的磁偶极超精细结构常数.     

Kq, Scaling of ac susceptibility and the nonlinear response function of high-temperature superconductors

The amplitude-dependent ac susceptibility of high-temperature superconductors is shown to obey some empirical scaling relations. We try to analyze this behavior by extending a dc nonlinear response function of mixed state to the ac cases. The derived equations for critical current and ac susceptibility ξ(T) agree with the scaling relations of experimental data.     

非同轴结构高温超导推力轴承的悬浮力

基于宏观电磁场的临界态Bean模型,利用商用电磁场有限元分析软件ANSYS,对由非同轴的单块高温超导体和整块永磁体组成的高温超导推力轴承静态特性进行了数值研究,分析了永磁体的结构参数对高温超导推力轴承静态悬浮力的影响。     

LK-99的半磁悬浮和高温超导体的锁定磁悬浮

基于电磁学和超导物理学的原理和相关实验数据,说明所谓的室温常压超导体LK-99在圆盘状钕铁硼永磁体极面的半悬浮应来源于其中的铁磁杂质碎片所受的转矩和引力。涂覆Y-Ba-Cu-O的高温超导体薄片在这种永磁体磁极上下的锁定悬浮,则起因于不均匀外磁场中超导体位置变化感生的超导电流所受该磁场的位置回复洛伦兹力,而并非迈斯纳效应和所谓的量子锁定的结果。     

The solution of a wedge disclination dipole interacting with an annular inclusion and the force acting on the disclination dipole

The interaction between a wedge disclination dipole and an elastic annular inclusion is investigated. Utilizing the Muskhelishvili complex variable method, the explicit series form solutions of the complex potentials in the matrix and the inclusion region are derived. The image force acting on the disclination dipole centre is also calculated. The influence of the location of the disclination dipole and the thickness of the annular inclusion as well as the elastic dissimilarity of materials upon the equilibrium position of the disclination dipole is discussed in detail. The results show that a stable equilibrium point of the disclination dipole near the inclusion is found for certain combinations of material constant. Moreover, the force on the disclination dipole is strongly affected by the position of the disclination dipole and the thickness of annular inclusion. The repulsion force increases （or the attraction force reduces） with the increase of the thickness of the annular inclusion. An appropriate critical value of the thickness of the annular inclusion may be found to change the direction of the force on the disclination dipole. The present solutions include previous results as special eases.     

高温超导磁悬浮轴承悬浮力数值分析

高温超导磁悬浮轴承已经被广泛应用到飞轮储能系统之中,它的主要结构是由高温超导体和永磁体组成。本论文基于有限元法(FEM)和临界态模型,对高温超导推力轴承的悬浮力和刚度等参数进行模拟仿真,并且在SCML-02测试装置上进行测试,计算结果与测试结果得到很好的吻合。并且进一步对环形永磁体推力轴承进行计算模拟,为进一步的轴承结构参数优化做好基础。