Anisotropy of Electronic Spin Texture in the High-Temperature Cuprate Superconductor Bi2Sr2CaCu2O8+δ

Seeking new order parameters and the related broken symmetry and studying their relationship with phase transition have been important topics in condensed matter physics. Here, by using spin-and angle-resolved photoemission spectroscopy, we confirm the helical spin texture caused by spin-layer locking in the nodal region in the cuprate superconductor Bi₂Sr₂CaCu₂O_8+δ and discover the anisotropy of spin polarizations at nodes along Γ –X and Γ –Y directio...     

LECTRONIC STRUCTURE STUDIES OF Bi2Sr2CaCu2-xSnxO8+δ SYSTEM

Photoemission measurements have been carried out for Bi₂Sr₂CaCu_2-xSn_xO_8+δ system with conventional x-ray photoemission spectroscopy for core-level spectra and synchrotron radiation photoemission spectroscopy for valence band. With Sn doping, all core levels shift differently in binding energy, and the intensity near fermi energy becomes smaller in valence hand. From the experiment, we can deduce that the shifts of all core levels and valence hands may involve some other mechanisms, such ms electrostatic effects, in addition to binding energy referencing effects. We argue that the chemical environment plays a crucial role in the electronic structure of high-temperature superconductors.     

在H2气氛中Bi2Sr2CaCu2O8+δ的热处理效应

对高品质单相多晶Bi₂Sr₂CaCu₂O_8+δ样品作真空或H₂气氛中不同温度下的热处理。由X射线结构分析,其正常态和超导态性质(特别是载流子浓度)的系统测量结果表明:Bi₂Sr₂CaCu₂0_8+δ样品在H₂气氛中热处理,其氧的释放可分为两个阶段:一是Bi-O层之间的过量氧原子的逸出,降低系统的载流子浓度,从而调节T_c;二是CuO₂面内氧原子的迁移,产生氧空位,使CuO₂面内Cu²⁺的短程二维反铁磁(2D-AFM)有序背景遭到破坏。可以认为:以往文献中报道的Bi₂Sr₂CaCu₂O_8+δ超导体的吸氢效应导致T_c的变化,很可能主要的并不是氢原子的电子掺杂行为,而是与吸氢过程中氧含量的变化相联系。 关键词：     

不同氧含量Bi2Sr2CaCu2O８+δ单晶电阻率的各向异性

精确测量了在不同氧压下退火的单晶Bi₂Sr₂CaCu₂O_8+δ(Bi2212)样品的Cu-O面内和Cu-O面外的电阻率ρ_c(T)和ρ_ab(T).发现ρ_c(T)和各向异性比(ρ_c(T)/ρ_ab(T))随着载流子浓度增加而迅速下降.在过掺杂样品中,高于120K时,ρ_c随温度线性下降,而各向异性 关键词：     

Bi2Sr2CaCu2-xSnxO8+δ系列 超导体的XRD和XPS研究

实验研究了Bi₂Sr₂CaCu_2-xSn_xO_8+δ 的X射线衍射(XRD)和光电子能谱(XPS).实验发现随着掺杂(Sn)量的增加,晶格参数a 和c都有所变化,O1s和Cu2p芯能级谱也发生了变化.实验结果表明： 在低掺杂量时,Sn主要 呈二价态;而在高掺杂浓度时呈四价态;掺Sn对超导电性的影响与其他元素的掺杂不同.这 些实验结果支持化学环境在高温超导样品的电子结构中起着重要作用的结论. 关键词： Bi系超导体 掺杂 X射线衍射 光电子能谱     

Thermodynamic parameters of Bi2Sr2CaCu2O8+δ thin film prepared by molecular beam epitaxy

Bi₂Sr₂CaCu₂O_8+δ (Bi2212) thin film is an important superconducting material ascribed to its high transition temperatures and low toxicity, but the application of Bi2212 thin films is limited due to the appearances of intergrowth and impurity phases. To achieve high-quality Bi2212 thin film by molecular beam epitaxy (MBE), the oxidizing gas pressure and substrate temperature are the key parameters. Here, the phase formation in Bi-based thin films grown by MBE was studied as a function of oxidizing gas pressure and substrate temperature. Furthermore, the thermodynamic parameters have been investigated through enthalpy change. This study indicates that the substrate temperature was increased with the enhancing of ozone partial pressure when the composition ratio is fixed, Bi2212 single phase can be formed. Moreover, the chemical stability decreases in the order of Bi₂Sr₂CuO_6+δ > Bi2212 > Bi₂Sr₂Ca₂Cu₃O_10+δ.     

Bi2Sr2CaCu2O8的晶体结构与超导性能

本文研究了Bi-Sr-Ca-Cu-O体系中理想成份为Bi₂Sr₂CaCu₂O₈化合物的超导性能和晶体结构。名义成份为BiSrCaCu₂O_5.5零电阻超导转变温度T_c(0)=81.5K。用X射线粉末衍射方法测定了Bi₂Sr₂CaCu₂O₈的晶体结构,其基本结构属体心四方晶系,空间群为D_4h¹⁷-l4/mmm,点阵常数a=3.825?,c=30.82?。每单胞化合式单位为2.2Ca占据2(a)等效点系,4Sr,4Bi和4Cu占据三组4(e)位置,其原子参数z分别为0.110,0.302和0.445,16O分别占据8(g),z=0.445和二组4(e),z=0.210和0.380。Bi₂Sr₂CaCu₂O₈晶体结构可认为是阳离子沿z轴的(00z)和((1/2)(1/2)z)交错排列,由Aurivillius相导生出来的。讨论了在Bi-Sr-Ca-Cu-O体系中可能存在的其它沿z轴不同堆垛层数的超导相。 关键词：     

Bi2Sr2CaCu2O8+y掺Na样品的超导机制

用熔融法制备了Bi₂Sr₂CaCu₂O_8+y掺Ｎａ多晶样品，转变温度Ｔ_c提高到９０Ｋ以上，最大的零电阻温度达到９２．５Ｋ。在流动氧气退火后，未掺Ｎａ样品Ｔ_c显著降低，而掺Ｎａ样品Ｔ_c几乎不变，说明二者Ｔ_c提高具有不同的机制。据此我们认为Ｎａ替代了Ｂｉ而使Ｂｉｏ层电荷失去平衡，Ｃｕｏ面上电子转移到Ｂｉｏ层而形成空穴，空穴和电子的吸引相 关键词：     

Fiske steps in surface intrinsic Josephson junctions of Bi2Sr2CaCu2O8+δ single crystals

Current－voltage characteristics of the surface intrinsic Josephson junctions under a magnetic field parallel to CuO_2 planes have been studied experimentally. Fiske steps in such a junction have been observed. The Swihart velocity for the junction is found to be 7.2×10^5m/s, which corresponds to the velocity mode of a single junction.     

Electronic Evolution from the Parent Mott Insulator to a Superconductor in Lightly Hole-Doped Bi2Sr2CaCu2O8+σ

High temperature superconductivity in cuprates is realized by doping the Mott insulator with charge carriers. A central issue is how such an insulating state can evolve into a conducting or superconducting state when charge carriers are introduced. Here, by in situ vacuum annealing and Rb deposition on the Bi₂Sr₂Ca_0.6Dy_0.4Cu₂O_8+σ(Bi2212) sample surface to push its doping level continuously from deeply underdoped(T_c = 25...     

Bi2Sr2CaCu2O8单晶中的反常尖锋效应

使用牛津震动样品磁强计(VSM)研究了Bi₂Sr₂CaCu₂O₈单晶的磁滞回线.在20到40K温度之间发现了反常的尖锋效应,随样品O含量的增加,发生尖锋效应的外场也相应提高.可以认为在尖峰效应处发生了由涡漩物质的有序固态到无序固态的相变,在有少量点缺陷存在的BSCCO单晶相图上,B_sp线终止于20K温度处,在20K以下温区没有发生准格子到涡漩玻璃的相变,涡漩固相始终以准格子形式存在;可以认为尖峰效 关键词： 2Sr₂CaCu₂O₈单晶')" href="#">Bi₂Sr₂CaCu₂O₈单晶 磁滞回线 尖锋效应 相变     

Bi2Sr2CaCu2O8超导单晶中的电阻反常行为

测量了Bi₂Sr₂CaCu₂O₈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(>100Gs)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. 关键词： 2Sr₂CaCu₂O₈单晶')" href="#">Bi₂Sr₂CaCu₂O₈单晶 反常电阻峰 准再入行为     

Bi2Sr2CaCu2O8单晶a-b平面热电势率的各向异性

测量了Bi₂Sr₂CaCu₂O₈单晶a方向的热电势率S_a和b方向的热电势率S_b与温度T的关系,发现在a-b平面内热电势率存在各向异性。认为S_a与S_b的差异来源于b方向的调制结构,并用扩散热电势率S_d,声子曳引热电势率S_g和相关跳跃热电势率S_h三种贡献,对实验结果进行了 关键词：     

Fermi-arc superconductivity, pseudogap and charge order in Bi2Sr2CaCu2O8+δ

We report STM/STS observations on the 4a×4a charge order in the pseudogap (PG) and superconducting (SC) states of Bi₂Sr₂CaCu₂O_8+δ, and suggest that the charge order is associated with incoherent quasiparticle or pair states around the antinodal fermi surface (FS), which are also responsible for the PG, and it can coexist with the superconductivity caused by the pairing of coherent quasiparticles on the nodal fermi arc. We also suggest that the nanometer-scale gap inhomogeneity in the SC state, reported previously [Pan, et al., Nature 413 (2001) 282; Mommo, et al., J. Phys. Soc. Jpn. 74 (2005) 2400; Hashimoto, et al., Phys. Rev. B74 (2006) 064508] arises from that in the PG state, which occurs around the antinodal FS.     

Pairing modulations and phase separation instabilities in Bi2Sr2CaCu2O8 + δ

There is growing evidence that the unconventional spatial inhomogeneities in the doped high-_Tc$T_c$ superconductors are accompanied by the pairing of electrons, subsequent phase transitions and condensation into coherent states. We show that such pairing states can be obtained from phase separation instabilities near level crossings. Conditions for coherent pairing instabilities are examined using exact diagonalization of Hubbard-like pyramid structures under variation of coupling and interaction strengths. We also evaluate the behavior of the energy charge gap in the vicinity of level crossings using a parametrization of coupling to the apical site to represent out-of-plane effects. These results provide a simple microscopic explanation of (correlation induced) supermodulation of the coherent pairing gap observed in scanning tunneling microscopy measurements at atomic scale in Bi₂Sr₂CaCu₂O_8 + δ.     

Bi2Sr2CaCu2-xLixOy体系的光电子能谱研究

采用X射线光电子能谱对Bi₂Sr₂CaCu_2-xLi_xO_y体系在真空中获得的清洁表面进行了研究。结果表明:Li的掺入对Bi和Sr的化学键性质几乎没有影响,而Ca,Cu,O的化学键性质有较大的变化,其结合能随着Li含量x的增加向高能方向移动。同时对真空中获得的清洁表面和普通表面样品O1s进行了比较,结果发现真空中获得的清洁样品O1s有一个峰(528.4eV),而普通表面样品O1s有两个峰(528.4eV)和(531eV),这表明O1s的高能峰是由污染产生的。 关键词：     

Bi2Sr2CaCu2Oy单晶调制结构的X射线衍射研究

用Ｘ射线转靶衍射仪，详细地观察和分析了Bi₂Sr₂CaCu₂O_y单晶的调制结构．指出布喇格反射的卫星峰是沿ｃ^*拉长的，与Ｂ心正交对称结构不相符的宽化峰正是由于这种拉长的结果，且导致卫星峰强度的不对称性．Ｂｉ-Ｏ层和钙钛矿层晶格失配形成的超晶格为非正交而是单斜的，并可能存在超晶格孪晶     

Bi2Sr2CaCu2O8 crystal with a region of periodic blind antidots – transition between bulk and interface vortex pinning

This work focuses on differential magneto-optical two-dimensional imaging of the current distribution in a high-T_c superconducting Bi₂Sr₂CaCu₂O₈ crystal having a region of 170 × 170 μm² patterned with periodic blind antidots. By measuring the self-induced field of an applied current, we can map the current flow distribution within and at the edges of the patterned region. We detected three separate types of current flow within the patterned region, which correspond to three different arrangements of pancake vortices within and at the edges of the patterned region. At high temperatures the vortices delocalize from the antidots, presumably due to thermal fluctuations. However, at lower temperatures vortex pinning mechanisms become prominent, lowering the vortex mobility in the patterned region. There are two contributing mechanisms: bulk pinning by the patterned antidots and interface pinning due to an entry barrier into the patterned region. Each mechanism is dominant at different temperatures. From our experiments we see that the T–H transition line from the bulk to the interface pinning and the vortex melting line in the pristine region coincide.     

用自助熔剂法生长Bi2Sr2CaCu2Oy单晶的特点

用Ｂｉ₂Ｏ₃作自助熔剂，对Ｂｉ-２２１２单晶的生长特点作了较为细致的实验研究．就助熔剂含量、热循环、坩锅的污染、熔体的非共熔性、各向异性生长速度以及Ｂｉ-２２０１相的共生等晶体生长中普遍存在的诸多问题进行了深入的探讨