FLUCTUATIONS OF FLUX LINES ON THE SURFACE OF SUPERCONDUCTOR

In this paper, we study the magnetic structure of the half-ring flux line ended on the surface of a superconductor. The elemental modes for these half-ring flux lines are the half-ellipse flux lines ended on and perpendicular to the surface. The statistics of these half-ring flux lines is, in a certain degree, similar to the vortex-antivortex pairs in thin superconducting films. An abrupt change of the thermodynamic properties for this system takes place at a temperature lower than T_c. It is analogous to the KT transition in thin superconducting films in certain sense.     

Nernst effect in Tl-Ba-Ca-Cu-O superconducting films due to infrared laser heating

A Nernst effect has been observed in a high temperature superconductor for the first time. Irradiating superconducting Tl–Ba–Ca–Cu–O thin films by short pulses of a TEA-CO₂ laser, a photovoltaic signal is detected perpendicular to a magnetic field applied parallel to the film surface. The signal is attributed to magnetic flux line depinning and flux line transport driven by the laser induced temperature gradient. The results are described by thermal flux line activation leading to a calculated distribution of pinning energies from 100 K to 4000 K.     

Low-field vortex dynamics in various high-T c thin films

We present a novel ac susceptibility technique for the study of vortex creep in superconducting thin films. With this technique we study the dynamics of dilute vortices in c-axis oriented Y-123, Hg-1212, and Tl-1212 thin films, as well as a axis oriented Hg-1212 thin films. Results on the Hg-1212 and Tl-1212 thin films indicate that dislocation-mediated plastic flux creep of single vortices dominates at low temperatures and fields. As the temperature (or the field) is increased, the increasing vortex-vortex interactions promote a collective behavior, which can be characterized by elastic creep with a non-zero μ exponent. Also, in some of these samples effects of thermally assisted quantum creep are visible up to 45 K in some of these samples. In Y-123 thin films, creep is found to be collective down to the lowest temperatures and fields investigated, while the quantum creep persists only up to 10–11 K.     

高温超导薄膜微波非线性研究的进展

文章介绍了高温超导薄膜微波非线性的主要特征，阐述了高温超导薄膜微波非线性产生的原因和相关的研究现状，指出了高温超导薄膜非线性研究中遇到的困难和尚未解决的问题．     

纳米粒子在不锈钢衬底MgB2超导膜中的作用

我们用混合物理化学气相沉积法(hybrid physical-chernical vapor deposition简称为HPCVD)以氩气为背景气体,在不锈钢衬底上于不同条件下制备了一批MgB2超导薄膜样品.用扫描电子显微镜获取了相关的SEM图像,并对膜的成分进行了能谱分析(EDX)的.当把不锈钢衬底MgB2超导薄膜弯曲不同角度之后,膜面上均出现了裂纹.裂纹的数量和宽度随弯曲的角度的增大而增加,但是膜始终紧紧地覆着在衬底上不脱落.因此我们可以说覆着在不锈钢衬底上的MgB2超导薄膜具有了很好的韧性.在膜中我们也发现有大量的数十纳米大小的晶粒.这个尺寸的纳米粒子的作用可以用来平衡MgB2膜内结构和表面晶粒的活性之间的相互作用.MgB2纳米粒子的存在是MgB2超导膜表现出韧性的关键角色.     

Ginzberg-Landau理论对超导薄膜的适用性

本文指出虽然三十年来Ginzberg-Landau理论(以下简称G-理论)被人们广泛地用于描述超导薄膜的临界场,而且它还是描述强耦合超导薄膜临界场的唯一理论,但G-L关于薄膜临界场的理论不仅一直未得到实验证明,而且它既不能用于描述结晶态的弱耦合超导薄膜的临界场,也不适用于描述强耦合超导薄膜的临界场。本文还提出了一个在薄膜极限下定域的新判据:ξ<<λ,ξ<关键词：     

三相电抗器型高温超导限流器的阻抗与动态仿真

三相电抗器型超导故障限流器(SCFCL)由三个同匝数的超导绕组绕在单一铁芯上组成，正常工作时阻抗为零，接地短路时，相当于串联了一个大电感，若发生三相或两相短路，其电阻突然增大；本分析了它在各种运行状态下其铁芯内的磁通变化，推导出了相应的阻抗公式；设计了一个小型样机，并对该样机的进行了动态仿真，其结果与理论分析一致．     

Local Observation of Field Polarity Dependent Flux Pinning by Magnetic Dipoles

A scanning Hall probe microscope is used to study flux pinning in a thin superconducting Pb film covering a square array of single-domain Co dots with in-plane magnetization. We show that single flux quanta of opposite sign thread the superconducting film below T(c) at the opposite poles of these dipoles. Depending on the polarity of the applied field, flux lines are attracted to a specific pole of the dipoles, due to the direct interaction with the vortexlike structures induced by the local stray field.     

高温超导薄膜无源微波器件的应用

高温超导薄膜在微波器件中的应用,与常规导体相比可以减小器件的体积,重量,功率消耗和插入损耗,并且可以在液氮沸点附近工作,接近于卫星的环境温度100K,微波器件是在几个平方厘米的高温超导薄膜上制备的。这些薄膜必须要有最高的超导性能,如临界温度,临界电流密度以及微波表面电阻,因此高温度超导薄膜的应用受到制备大面积,高质量薄膜的限制,美国高温超导空间实验在1999年5月已经获得成功,使高温超导薄膜在微波器件中的应用成为现实。     

Electronic structure and nematic phase transition in superconducting multiple-layer FeSe films grown by pulsed laser deposition method

We report comprehensive angle-resolved photoemission investigations on the electronic structure of single crystal multiple-layer FeSe films grown on CaF_2 substrate by pulsed laser deposition(PLD) method. Measurements on FeSe/CaF_2 samples with different superconducting transition temperatures T_c of 4 K, 9 K, and 14 K reveal electronic difference in their Fermi surface and band structure. Indication of the nematic phase transition is observed from temperature-dependent measurements of these samples; the nematic transition temperature is 140-160 K, much higher than ~90 K for the bulk FeSe. Potassium deposition is applied onto the surface of these samples; the nematic phase is suppressed by potassium deposition which introduces electrons to these FeSe films and causes a pronounced electronic structure change. We compared and discussed the electronic structure and superconductivity of the FeSe/CaF_2 films by PLD method with the FeSe/SrTiO_3 films by molecular beam epitaxy(MBE) method and bulk FeSe. The PLD-grown multilayer FeSe/CaF_2 is more hole-doped than that in MBE-grown multiple-layer FeSe films. Our results on FeSe/CaF_2 films by PLD method establish a link between bulk FeSe single crystal and FeSe/SrTiO_3 films by MBE method, and provide important information to understand superconductivity in FeSe-related systems.     

化学气相沉积-后退火法制备MgB2超导薄膜

本文提出在高真空镀膜系统中通过化学气相沉积(CVD)的方法沉积高纯度的先驱B膜,再经过后退火工艺,Mg扩散进入先驱膜而反应生成了MgB2超导薄膜.经过多种实验方法检测,这种薄膜具有较为优异的超导性能,是一种和传统微电子工艺兼容、适宜于工业化大规模生产MgB2超导薄膜的方法.     

Thermally assisted flux flow in MgB2: strong magnetic field dependence of the activation energy

The origin of the resistive transition broadening of superconducting MgB₂ thin films is investigated. Thermally activated flux flow is found to be responsible for the resistivity in the vicinity of the critical temperature. The activation energy for flux motion is observed to have an extraordinary strong dependence on the magnetic field. The results are discussed.     

Is the Static Magnetic Vector Potential Screened by a Thick Superconducting Shield

In 1986 Tonomura and his co-workers reported the results of a test for the existence of the magnetic Aharonov-Bohm (AB) effect using permalloy toroids with a superconducting niobium coating. Classical Maxwell theory suggests that the group may have been able to observe the AB effect only because their superconducting shield was quite thin (2.5 penetration depths), and that, had a very thick shield been used, no AB effect would have been observable. However, orthodox quantum mechanics predicts that a static vector potential penetrates a superconducting shield of any thickness in cases where the magnetic flux inside the sample is an odd integer times h/2e. Regardless of which view is correct, it is argued in this paper that a superconductor only screens leakage or fringing field to the extent that it screens vector potential, so that there are doubts that the experiment answered the critics of earlier experiments, as was claimed.     

超导薄膜表面电阻测量新方法

本文报导一种测量高温超导薄膜微波表面电阻的新方法和测试装置.通过对加载两个不同蓝宝石的同一谐振腔进行测试,可以得到测试样品以外所有其它损耗对应的Q值.根据电磁场分布计算出谐振腔的结构参数G.用网络分析仪测量出谐振腔的无载Q值,便可计算出超导薄膜的微波表面电阻Rs.测量过程中既不会损伤超导薄膜样品,同时可以实现单片超导薄膜表面电阻的绝对测量,不需要校准件,测量简便可靠,精度高.     

Superconducting mechanism of YBaCuO superconductors

Electromagnetic properties of YBaCuO superconductor were measured on applying an external magnetic field to study non-volatile magnetic effect. The voltage increases with increase in applied magnetic flux, but it becomes constant at about 10⁻² T. The appearance of the voltage is ascribed to the trapping of magnetic flux. By changing the density of external magnetic flux, changes in inductance of a coil in which a superconducting bar inserted were also measured. The results showed that the filament model was valid to explain the mechanism of the occurrence of a voltage in superconducting sample. It was concluded that the electromagnetic properties arose from the interaction between the trapped magnetic flux and weak link of the filament formed in the superconducting bulk.     

Enhanced vortex damping by eddy currents in superconductor-semiconductor hybrids

An enhancement of vortex-motion damping in thin Pb/In superconducting films is obtained through coupling to an adjacent two-dimensional electron gas formed in a modulation-doped GaAs/AlGaAs heterostructure. This effect is observed by monitoring the power dissipation in the superconductor in the vortex state while increasing the density of the electron gas using a gate voltage. Quantitative agreement is found with calculations based on a viscous damping model which considers generation of eddy currents in the electron gas by moving flux lines. In the regime of filamentary vortex flow, eddy-current damping leads to a striking dissipation breakdown due to the stopping of entire vortex channels.     

Electronic transport properties of topological insulator films and low dimensional superconductors

In this review, we present a summary of some recent experiments on topological insulators （TIs） and superconducting nanowires and fihns. Electron electron interaction （EEI）, weak anti-localization （WAL） and anisotropic magneto-resistance （AMR） effect fbund in topological insulator fihns by transport measurements are reported. Then, transport properties of superconducting films, bridges and nanowires and proximity effect in non-superconducting nanowires are described. Finally, the interplay between topological insulators and superconductors （SCs） is also discussed.     

EFFECTS OF THE QUALITY OF SUBSTRATE ON THE STRUCTURE AND SUPERCONDUCTING PROPERTIES OF Yba2Cu3O7-x THIN FILM

We have systematically investigated the structures, morphologies, microwave surface resistance, DC performances and the substrate qualities of three YBa₂Cu₃O_7-x(YBCO) thin films 30mm in diameter. The three samples deposited by the same process have been proved of different properties. It has been shown that the structure and superconducting properties of the thin film depend strongly on the quality of substrate.     

在小型制冷机中测量薄片交流磁化率以决定超导转变温度的装置

本文介绍了一种利用电磁感应原理和超导磁效应,在小型制冷机中测量超导体转变温度的装置.本装置包括密闭的真空室、压缩制冷机、真空泵、真空计、锁相放大器、温控仪、计算机、线圈绕组.其中,线圈绕组置于真空室内,由初级线圈和次级线圈组成,初级线圈和次级线圈分别绕制在两个线圈骨架上;被测超导薄片材料放置于初级线圈和次级线圈之间;压缩制冷机用来为超导材料制冷;真空泵用来对真空室抽真空;温控仪用来测量和控制真空室内的温度;锁相放大器为初级线圈提供交流电压信号,并测量次级线圈的电信号以得到交流磁化率值;计算机记录温控仪测得的温度数据和锁相放大器测得的次级线圈的电压信号,并显示锁相放大器测得的次级线圈的电压信号随温度变化的曲线.实验证明该装置可以通过测量超导体交流磁化率的变化测得超导转变温度,具有自动化测量及测试成本低等特点.     

原位法MgB_2-B_4C复相超导体合成及相含量调控研究

以B4C和Mg为原料合成的MgB2-B4C复相超导体具有高的临界电流密度(Jc)和高的超导转变温度(Tc),是一种有潜力的实用MgB2超导材料,其成相机理对复相MgB2超导体的相含量调控和磁通钉扎研究具有重要意义。结合经典烧结理论,研究了B4C-Mg真空固相烧结制备MgB2-B4C复相超导体的超导相形成和晶粒生长过程,给出了B4C-Mg的金斯特林格扩散模型和MgB2晶粒生长过程。通过选择B4C原料粒径,MgB2-B4C复相超导体超导相体积相含量在18%-88%范围可控。相含量88%的MgB2-B4C复相超导体临界转变温度达33.5K,转变宽度1.5K。10 K环境6T外场下电流密度可以达到1×104A/cm2,表明MgB2-B4C复相超导体具有良好的磁通钉扎行为。