ESTIMATES OF LOWER CRITICAL MAGNETIC FIELD AND VORTEX PINNING BY INHOMOGENEITIES IN TYPE Ⅱ SUPERCONDUCTORS

The effect of an applied magnetic field on an inhomogeneous superconductor is studied and the value of the lower critical magnetic field Hc1 at which superconducting vortices appear is estimated. In addition, the authors locate the vortices of local minimizers, which depends on the inhomogeneous term a(x).     

不同碱金属叠氮化物对层状晶体β-MNCl(M=Zr,Hf)电子掺杂的影响

通过使用各种不同的碱金属叠氮化物RN3(R=Li,Na,K,Rb)与层状晶体βMNCl(M=Zr,Hf)发生反应,并控制RN3与βMNCl反应的摩尔比对βMNCl进行电子掺杂.所有的生成物都显示了超导性,βZrNCl系列的起始超导转变温度均为13.5K,而βHfNCl系列的起始超导转变温度均为23.5K.但是,不同的碱金属叠氮化物具有不同的可反应性,其反应产物也具有不同的性质,例如超导体积百分率、晶格常数、热稳定性和在空气中的稳定性等都和碱金属离子有关.SQUID测试结果表明,NaN3和KN3分别是βZrNCl和βHfNCl最好的电子掺杂反应剂.     

4M-2000A超导电缆小型制冷系统的设计计算

为了配合 4 M- 2 0 0 0 A超导电缆系统的研制 ,并为 30 M- 2 0 0 0 A超导电缆制冷系统设计、计算提供实际试验值和运行经验 ,设计、建立了 4 M- 2 0 0 0 A超导电缆小型制冷系统。文中叙述了 4 M- 2 0 0 0 A超导电缆制冷系统的设计要求、系统流程、设计概算 ,制冷系统的主要设备介绍以及调试结果等。     

MgB_2超导体输运特性的研究

文中对 Mg B2 超导体的制备过程 ,对其同位素效应、电阻率、I- V曲线、热电势、电导涨落效应、能隙、霍尔效应、热重 -差热分析实验等输运特性进行了较全面的综述 ,并讨论了在 Mg B2 超导体基础上的元素替代效应。     

Superconductivity in Mo5SiB2

In the Mo-Si binary system, Mo₅Si₃ crystallizes in the W₅Si₃ (T₁ phase) structure type. However, when boron replaces silicon in this compound, a structural transition occurs from the W₅Si₃ prototype structure to the Cr₅B₃ prototype structure (T₂ phase) at the composition Mo₅SiB₂. Mo₅SiB₂ has received much attention in the literature as a candidate for structural application in high-temperature turbines, but its electronic and magnetic behavior has not been explored. In this work, we show that Mo₅SiB₂ is a bulk superconducting material with critical temperature close to 5.8 K. The specific-heat, resistivity and magnetization measurements reveal that this material is a conventional type II BCS superconductor.     

Disordered magnetic phases and magnetic transitions in non anisotropic frustrated systems

Numerous studies have been devoted to disordered magnetic phases which show the existence of several types of disorder in non-anisotropic systems. Semi-disordered systems which retain at least partially long-range order (reentrant properties and randomly canted structures) and fully disordered systems (spin cluster and soft transition systems, true spin glass state) are shortly reviewed. Several characteristic experiments and results are presented and commented on, such as alternative, nonlinear and static susceptibilities, thermoremanence, ageing effects, neutron diffraction and Mössbauer spectroscopy. The possible types of disordered magnetic phases are discussed as a function of a sharp (or soft) transition and of a more or less fast dynamics. In true spin glasses, some problems are still open while in the other disordered phases the unresolved questions are numerous.     

Above-gap and subgap differential conductance anomaly in concentrated magnetic semiconductor Zn0.32Co0.68O1 − v/Pb superconductor hybrid junctions

The Zn_0.32Co_0.68O_1 − v/Pb hybrid junctions were prepared, where the concentrated magnetic semiconductor Zn_0.32Co_0.68O_1 − v is in the region of variable range hopping transport instead of the ballistic or diffusive transport. The high differential conductance peak at gap voltage and two above-gap peaks were observed below the superconducting critical temperature. Moreover, both the zero bias conductance peak and the finite bias conductance peak were observed below the gap voltage. All these differential conductance peaks systematically evolve and finally disappear as the temperature or the magnetic field increases. These transport phenomena were explained by phase coherent Andreev reflection in the presence of strong disorder, magnetic impurity scattering, and spin polarization.     

基于小型低温制冷机的高温超导材料超导转变温度测量装置

高温超导材料的超导转变温度是判断超导材料性能优劣的一个重要指标,而超导材料转变温度的测量一般采用输运方法进行电阻随温度变化来确定.本文介绍一种新近研制的基于低温制冷机的高温超导材料超导转变温度测量装置,能有效的将样品温度从室温连续均匀的降至35K,通过Lab VIEW编写的数据采集系统人机界面,采用电流换向技术消除热电势,可以准确测量出超导材料的超导转变温度.经实验验证,该测量装置测量精确和重复性良好,可作为有效判定高温超导材料性能优劣的一种手段.