反常输运性质Bi2Sr2CaCu2O8单晶的生长

使用自助熔剂融化法成功的制备了Bi2Sr2CaCu2O8超导单晶。在对所得单晶进行输运性质的研究时,我们发现一种反常扔物理特征：在超导涨落区观察到反常的电阻峰,从Bi2Sr2CaCu2O8单晶的颗粒超导电性方面我们给出了合理的解释。     

Bi2Sr2CaCu2O8掺杂MgB2的磁通钉扎特性

为了研究超导材料中高温超导相颗粒的钉扎行为，在Ar气保护条件下，采用固相反应法制备了质量百分比为0，3，5和10％BizSr2CaCu2O8含量的MgB2块状样品．用X射线衍射和扫描电子显微镜对样品进行了显微结构分析；用物理性能综合测试系统振动样品磁强计（最大磁场9T）测量了所有样品在不同磁场下的直流M（T）曲线，并测量了不同温度下的准静态磁化曲线，通过Bean临界态模型分析出Jc（H）曲线．随着掺杂量的增大掺杂后Tc基本不变，转变宽度略为增大；相比于未掺杂样品，掺杂量为3wt％样品抗磁信号和临界电流密度有较大提高．显微结构分析结果表明，部分Bi2Sr2CaCu2O8分解为Cu2O和其它杂相，有部分Bi2Sr2CaCu2O8颗粒保留在样品内部，成为有效的钉扎中心．最后本文对超导体中的高温超导相颗粒的钉扎行为进行了分析．     

Bi2Sr2CaCu2O8掺杂MgB2的磁通钉扎特性

为了研究超导材料中高温超导相颗粒的钉扎行为,在Ar气保护条件下,采用固相反应法制备了质量百分比为0,3,5和10%Bi2Sr2CaCu2O8含量的MgB2块状样品.用X射线衍射和扫描电子显微镜对样品进行了显微结构分析;用物理性能综合测试系统振动样品磁强计(最大磁场9T)测量了所有样品在不同磁场下的直流M(T)曲线,并测量了不同温度下的准静态磁化曲线,通过Bean临界态模型分析出Jc(H)曲线.随着掺杂量的增大掺杂后Tc基本不变,转变宽度略为增大;相比于未掺杂样品,掺杂量为3 wt%样品抗磁信号和临界电流密度有较大提高.显微结构分析结果表明,部分Bi2Sr2CaCu2O8分解为Cu2O和其它杂相,有部分Bi2Sr2CaCu2O8颗粒保留在样品内部,成为有效的钉扎中心.最后本文对超导体中的高温超导相颗粒的钉扎行为进行了分析.     

Bi2Sr2CaCu2O8超导单晶中的电阻反常行为

测量了Bi2 Sr2 CaCu2 O8单晶的ab面和c轴方向电阻 ,在其超导转变温度附近发现了反常的电阻峰出现 .其随外磁场 (>10 0Gs)和电流的增加而逐渐消失 .文章认为这个反常的电阻峰是由于单晶中超导相的不均匀分布而导致的准再进入行为 .     

掺Pb的Bi-Sr-Ca-Cu-O超导体及非晶体的Raman光谱

本文研究了Bi2Sr2CaCu2O8单晶(Tc=85K)、Bi2-xPbxSr2Ca2Cu3Oy单相(Tc=107K)和Bi(Pb)-Sr-Ca-Cu-O非晶体室温下20-720cm-1的Raman光谱.通过谱图的比较,我们认为456-466、631-650cm-1是高Tc氧化物的特征谱,它们与Cu-O链及Cu-O面上的强电子-声子耦合有关;掺Pb导致Bi(Pb)-O双层之间氧的分布改变,增强了Bi(Pb)-O双层之间的耦合,从而有助于提高超导转变温度Tc.     

基于低温光声光谱技术的YBa2Cu3O7-δ超导转变过程

利用低温光声系统实时采集高Tc超导材料超导转变过程光声信号,是高Tc超导材料超导机理研究的一种新的实验方法。选取YBa₂Cu₃O_7-8超导体作为试样,分别构建常态→超导态（试样降温过程）和超导态→常态（试样升温过程）,得到转变过程光声信号对比图,并依据光声光谱图对试样失超现象作出可能的解释。     

《自然·物理》报道拓扑绝缘体/高温超导体近邻效应研究最新成果

清华大学物理系周树云研究组、陈曦/薛其坤研究组和清华大学高等研究院姚宏研究员,最近在拓扑绝缘体和高温超导体异质界面的超导近邻效应研究中取得重要进展.他们首次利用分子束外延（MBE）在高温超导体Bi2Sr2CaCu2O8＋d（BSCCO）上制备出高质量Bi2Se3拓扑绝缘体薄膜,     

用于微波滤波器的Tl2Ba2CaCu2O8超导薄膜

本文报导用磁控离子溅射和后热处理方法在LaAlO3(001)衬底上制作2英寸双面Tl2Ba2CaCu2O8(Tl-2212) 超导薄膜的方法和薄膜的特性.XRD测试表明薄膜具有纯的Tl-2212相和c轴垂直于膜面的织构.衬底两侧薄膜的结晶形貌和超导电性均匀,超导转变温度Tc一般为105 K左右,液氮温度下临界电流密度Jc>2×106A/cm2,10GHz频率下表面电阻最小达到350μΩ,可满足超导微波滤波器实用的需要.     

化学溶液法制备Bi-2212超导厚膜及表征

在柔性衬底上制备的Bi-2212(Bi2Sr2CaCu2O8+x)超导厚膜在高场低温下有高的临界电流密度、可塑性好、易加工成材等特点,因而有广阔的应用前景.所以制备低成本、高性能的Bi-2212厚膜技术已经成为此类高温超导材料实用化的关键.本文系统的研究了采用Bi系超导粉前驱化学溶液的方法进行Bi-2212超导厚膜的制备和表征.对制备超导厚膜过程中的关键步骤做了系统的研究,主要包括局部熔融烧结温度、固相烧结温度、匀胶机最高转速、涂层的厚度等对超导转变温度和转变宽度的影响.我们得出最佳的烧结温度和固相温度分别是888℃、845℃,并发现随着匀胶机转速和涂层厚度的增加,超导膜的转变温度逐步提高,当最高转速为4000r/min,涂层厚度设定为七层,制备出的超导膜R～T曲线的第二个相转变点消失了.制备出的超导膜的转变温度在90K左右.与此同时还进行了XRD、SEM测试表征.最终可以得到均匀平整无裂纹的高质量Bi-2212超导厚膜.     

共沉淀法合成Sm3+掺杂的Sr2CeO4的荧光光谱

以（NH4）2C2O4为沉淀剂，用Sr，Ce和Sm的硝酸盐为反应物，制备了Sr2CeO4：Sm的前驱体。将此前驱体烧结后，得到了Sm掺杂的Sr2CeO4白色荧光材料。其荧光光谱强度与烧结温度和Sm^3＋的掺杂浓度密切相关，当烧结温度为1050℃以及Sm^3＋的掺杂浓度为1mol％时，峰值为470nm的宽带以及Sm^3＋在608和654nm的线谱发射最强。同直接在高温固相反应下得到的样品进行比较，其发射光谱强度大大提高。     

Phase-coherence effects in vortex transport entropy

Nernst and electrical resistivity measurements in superconducting YBa2Cu3O7-delta and Bi2Sr2CaCu2O8+delta with and without columnar defects show a distinctive thermodynamics of the respective liquid vortex matter. At a field-dependent high temperature region in the H-T phase diagram, the Nernst signal is independent of structural defects in both materials. At lower temperatures, in YBa2Cu3O7-delta, defects contribute only to the vortex mobility, and the transport entropy is that of a system of vortex lines. The transition to lower temperatures in Bi2Sr2CaCu2O8+delta has a different origin; the maximum in the Nernst signal when decreasing temperature is not associated with transport properties but with the entropy behavior of pancake vortices in the presence of structural defects.     

Fourfold structure of vortex-core states in Bi2Sr2CaCu2O8+delta

We present a detailed study of vortex-core spectroscopy in slightly overdoped Bi2Sr2CaCu2O8+delta using a low-temperature scanning tunneling microscope. Inside the vortex core, we observe a fourfold symmetric modulation of the local density of states with an energy-independent period of (4.3 +/- 0.3)a0. Furthermore, we demonstrate that this square modulation is related to the vortex-core states which are located at +/-6 meV. Since the core-state energy is proportional to the superconducting gap magnitude , our results strongly suggest the existence of a direct relation between the superconducting state and the local electronic modulations in the vortex core.     

Scanning tunneling spectroscopy of Bi(2)Sr(2)CuO(6+delta): new evidence for the common origin of the pseudogap and superconductivity

Using scanning tunneling spectroscopy, we investigated the temperature dependence of the quasiparticle density of states of overdoped Bi(2)Sr(2)CuO(6+delta) between 275 mK and 82 K. Below T(c) = 10 K, the spectra show a gap with well-defined coherence peaks at +/-Delta(p) approximately 12 meV, which disappear at T(c). Above T(c), the spectra display a clear pseudogap of the same magnitude, gradually filling up and vanishing at T(*) approximately 68 K. The comparison with Bi(2)Sr(2)CaCu(2)O(8+delta) demonstrates that the pseudogap and the superconducting gap scale with each other, providing strong evidence that they have a common origin.     

Quasiparticles in the superconducting state of Bi(2)Sr(2)CaCu(2)O(8+delta)

Recent improvements in momentum resolution lead to qualitatively new angle-resolved photoemission spectroscopy results on the spectra of Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212) along the (pi,pi) direction, where there is a node in the superconducting gap. We now see the intrinsic line shape, which indicates the presence of true quasiparticles at all Fermi momenta in the superconducting state, and lack thereof in the normal state. The region of momentum space probed here is relevant for charge transport, motivating a comparison of our results to conductivity measurements by infrared reflectivity.     

Bi_2Sr_2CaCu_2O_(8+δ)单晶的钉扎力标度和磁通钉扎机制

测量了 Bi2 Sr2 Ca Cu2 O8+δ单晶不同温度下的磁化曲线。根据 Bean临界态模型得到了不同温度下的钉扎力密度 FP 对磁场的依赖关系 ,发现在不同温度下的钉扎力密度可以标度在同一条曲线上。标度函数和最大钉扎力所对应的磁场与不可逆场 Hirr的比值都表明 Si2 Sr2 Ca Cu2 O8+δ单晶在磁通玻璃态的钉扎机制主要是正常相面钉扎。     

Field-enhanced diamagnetism in the pseudogap state of the cuprate Bi2Sr2CaCu2O(8+delta) superconductor in an intense magnetic field

In hole-doped cuprates, Nernst experiments imply that the superconducting state is destroyed by spontaneous creation of vortices which destroy phase coherence. Using torque magnetometry on Bi2Sr2CaCu2O(8+delta), we uncover a field-enhanced diamagnetic signal M above the transition temperature Tc that increases with applied field to 32 Tesla and scales just like the Nernst signal. The magnetization results above Tc distinguish M from conventional amplitude fluctuations and strongly support the vortex scenario for the loss of phase coherence at Tc.     

Temperature dependent scattering rates at the fermi surface of optimally doped Bi(2)Sr(2)CaCu(2)O(8+delta)

For optimally doped Bi(2)Sr(2)CaCu(2)O(8+delta), scattering rates in the normal state are found to have a linear temperature dependence over most of the Fermi surface. In the immediate vicinity of the (pi, 0) point, the scattering rates are nearly constant in the normal state, consistent with models in which scattering at this point determines the c-axis transport. In the superconducting state, the scattering rates away from the nodal direction appear to level off and become temperature independent.     

Identification of a new form of electron coupling in the Bi2Sr2CaCu2O8 superconductor by laser-based angle-resolved photoemission spectroscopy

Laser-based angle-resolved photoemission measurements with superhigh resolution have been carried out on an optimally doped Bi(2)Sr(2)CaCu(2)O(8) high temperature superconductor. New high energy features at approximately 115 meV and approximately 150 meV, in addition to the prominent approximately 70 meV one, are found to develop in the nodal electron self-energy in the superconducting state. These high energy features, which cannot be attributed to electron coupling with single phonon or magnetic resonance mode, point to the existence of a new form of electron coupling in high temperature superconductors.     

Resonant spin excitation in an overdoped high temperature superconductor

An inelastic neutron scattering study of overdoped Bi(2)Sr(2)CaCu(2)O(8+delta) ( T(c) = 83 K) has revealed a resonant spin excitation in the superconducting state. The mode energy is E(res) = 38.0 meV, significantly lower than in optimally doped Bi(2)Sr(2)CaCu(2)O(8+delta) ( T(c) = 91 K, E(res) = 42.4 meV). This observation, which indicates a constant ratio E(res)/k(B)T(c) approximately 5.4, helps resolve a long-standing controversy about the origin of the resonant spin excitation in high temperature superconductors.