Nodal quasiparticles and antinodal charge ordering in Ca2-xNaxCuO2Cl2

Understanding the role of competing states in the cuprates is essential for developing a theory for high-temperature superconductivity. We report angle-resolved photoemission spectroscopy experiments which probe the 4a0 x 4a0 charge-ordered state discovered by scanning tunneling microscopy in the lightly doped cuprate superconductor Ca2-xNaxCuO2Cl2. Our measurements reveal a marked dichotomy between the real- and momentum-space probes, for which charge ordering is emphasized in the tunneling measurements and photoemission is most sensitive to excitations near the node of the d-wave superconducting gap. These results emphasize the importance of momentum anisotropy in determining the complex electronic properties of the cuprates and places strong constraints on theoretical models of the charge-ordered state.     

ZnFe2O4基磁凝胶的制备及磁性

用自形成法制备ZnFe2O4磁凝胶,并进一步研究包裹ZnFe2O4的γ-Fe2O3磁凝胶的制备,用振动样品磁强计(VSM)对ZnFe2O4和包裹ZnFe2O4的γ-Fe2O3磁性微粒及配制的胶体处在溶胶和凝胶的磁性测量.结果表明ZnFe2O4磁性微粒和胶体呈顺磁性,而包裹ZnFe2O4的γ-Fe2O3磁性微粒和胶体呈亚铁磁性.ZnFe2O4凝胶较其溶胶易磁化,而ZnFe2O4/γ-Fe2O3凝胶较其溶胶难磁化.从微观机制上解释了产生这些磁性差异的原因.

Abstract：

ZnFe2O4 magnetic gel is prepared by the self-formed method, and the preparation of γ-Fe2O3 coated with ZnFe2O4 is studied. The magnetization of ZnFe2O4 and γ-Fe2O3 nanoparticles coated with ZnFe2O4 and their gels and sols are measured by a vibrating sample magnetometer(VSM). The results show that the ZnFe2O4 powder and its colloid are paramagnetic, while the γ-Fe2O3 magnetic particles coated with ZnFe2O4 and colloid show ferrimagnetism. ZnFe2O4 gel is easier to be magnetized than sol. However, ZnFe2O4/γ-Fe2O3 gel is harder magnetized than sol. The reason for the difference in magnetization is interpreted microscopically.     

0.8ZnFe2O4-0.2MnFe2O4纳米颗粒磁化性质的实验研究

对采用化学共沉淀法制备的ZnFe2O4,MnFe2O4以及两者混合的3种纳米颗粒体的磁化性质进行了实验研究．在室温下测量了它们的磁化曲线,结果表明ZnFe2O4颗粒是顺磁性的,MnFe2O4及0.8Zn Fe2O4-0.2MnFe2O4混合颗粒呈超顺磁性．MnFe2O4颗粒的实验曲线和无相互作用的Langevin理论曲线间有较大偏差．混合颗粒体系的磁化强度不等于单独两种颗粒的磁化强度的简单相加．应用偶极子相互作用和颗粒团聚效应解释了MnFe2O4颗粒和混合颗粒体系的磁化性质．     

0.8ZnFe2O4-0.2MnFe2O4纳米颗粒磁化性质的实验研究

对采用化学共沉淀法制备的ZnFe2O4,MnFe2O4以及两者混合的3种纳米颗粒体系的磁化性质进行了实验研究.在室温下测量了它们的磁化曲线,结果表明ZnFe2O4颗粒是顺磁性的,MnFe2O4及0.8Zn Fe2O40.2MnFe2O4混合颗粒呈超顺磁性.MnFe2O4颗粒的实验曲线和无相互作用的Langevin理论曲线间有较大偏差.混合颗粒体系的磁化强度不等于单独两种颗粒的磁化强度的简单相加.应用偶极子相互作用和颗粒团聚效应解释了MnFe2O4颗粒和混合颗粒体系的磁化性质.     

Superconductivity in Alkaline Earth-Substituted La2CuO4-y

La(2)CuO4-y ceramics containing a few percent of Ca(2+), Sr(2+), and Ba(2+) ions have been prepared. Resistivity and susceptibility measurements exhibit superconductive onsets (as in earlier Ba(2+)-containing samples). The onset temperature La(2)CuO4-y with Sr(2+) is higher and its superconductivity-induced diamagnetism larger than that found with Ba(2+) and Ca(2+). This is proof that the electronic change resulting from alkaline earthdoping, rather than the size effect, is responsible for superconductivity. The ionic radius of Sr(2+) is close to that of La(3+) for which it presumably substitutes.     

Orbital ordering transition in La4Ru2O10

We report experimental evidence for a full orbital ordering transition in the two-dimensional lanthanum ruthenate La4Ru2O10. The observable consequences of this orbital ordering include the loss of the Ru local moment, a structural distortion which partitions Ru-O bonds into axially oriented short and long sets, a sharp jump in electrical resistivity, and the opening of a spin gap that is visible in neutron scattering experiments. This is a rare example of a discrete orbital ordering transition in a 4d transition metal oxide and demonstrates that orbital effects can have an influence on the properties of layered ruthenates, a family of compounds that notably includes the p-wave superconductor Sr2RuO4 and the field-tuned quantum critical metamagnet Sr3Ru2O7.     

Direct Observation and Analysis of CuO2 Shear Defects in La2-xSrxCuO4

Direct observations of CuO(2) sheet defect structures in superconducting La(2-x)Sr(x)CuO(4), with x in the range 0.05 crystallographic directions, by a pure shear mechanism along the edge of the octahedral copper-oxygen units. The line defects are partial screw dislocations, with characteristic displacement vectors of the type <(a/2), 0, (c/6)>, bounding the stacking faults. The existence of this type of defect demonstrates that there is an oxygen deficiency within the CuO(2) layers. However, unlike the open ReO(3) type-related structures, the packing density of the K(2)NiF(4) structure necessarily requires that anion defects be accompanied by the loss of cations of the A type (lanthanum, strontium). Under identical synthesis conditions, no defects are observed in the parent compound La(2)CuO(4).     

The Resonating Valence Bond State in La2CuO4 and Superconductivity

The oxide superconductors, particularly those recently discovered that are based on La(2)CuO(4), have a set of peculiarities that suggest a common, unique mechanism: they tend in every case to occur near a metal-insulator transition into an odd-electron insulator with peculiar magnetic properties. This insulating phase is proposed to be the long-sought "resonating-valence-bond" state or "quantum spin liquid" hypothesized in 1973. This insulating magnetic phase is favored by low spin, low dimensionality, and magnetic frustration. The preexisting magnetic singlet pairs of the insulating state become charged superconducting pairs when the insulator is doped sufficiently strongly. The mechanism for superconductivity is hence predominantly electronic and magnetic, although weak phonon interactions may favor the state. Many unusual properties are predicted, especially of the insulating state.     

磁性羧甲基纤维素基水凝胶的制备及其对Cu^2+的吸附行为

以羧甲基纤维素、β-环糊精和Fe3O4粒子为主要原料,采用接枝共聚法,制备了具有高吸附性能的磁性羧甲基纤维素基水凝胶(MHG)。采用FTIR、SEM等手段对MHG的物化结构进行了表征,用静态吸附的方法研究了MHG在不同温度和不同Cu^2+溶液质量浓度中的吸附行为,采用准一阶方程、准二阶方程对其吸附过程进行拟合。结果表明:MHG对蒸馏水的吸水量可高达5767 g/g,具有超优良的吸水效果。在不同质量浓度的Cu^2+溶液中,吸附量随着Cu^2+溶液质量浓度的升高而增多;当吸附温度为20~40℃时,MHG对Cu^2+的吸附量在吸附初期随着吸附温度的升高而增加,后期吸附量随吸附温度的增加变化不大。MHG对Cu^2+的最高吸附量可达465 mg/g,是一种优良的重金属离子吸附剂。     

CuFe2O4纳米微粒及其自形成磁性液体的磁性研究

对用共沉淀法制备的CuFe2O4磁性纳米微粒及其合成的自形成磁性液体在室温下进行磁性测量.其结果表明CuFe2O4微粒的饱和磁化强度较小,粉末与自形成磁性液体均呈超顺磁性-无剩磁、无矫顽力.用Langevin理论对测得的磁性进行了对比分析,从微粒间的相互作用解释了粉末和磁性液体的实测磁化曲线与Langevin理论的不同偏离现象.     

Oxygen Isotope Effect and Structural Phase Transitions in La2CuO4-Based Superconductors

The oxygen isotope effect on the superconducting transition temperature (alpha(o)) varies as a function of x in La2-xSrxCuO(4) and La2-xBaxCuO(4), with the maximum alpha(o) values (alpha(o) >/= 0.5) found for x near 0.12. This unusual x dependence implies that the isotope effect is influenced by proximity to the Abma --> P4(2)/ncm structural phase transition in these systems. Synchrotron x-ray difaction measurements reveal little change in lattice parameters or orthorhombicity due to isotope exchange in strontium-doped materials where alpha(o) > 0.5, eliminating static structural distortion as a cause of the large isotope effects. The anomalous behavior of alpha(o) in both strontium- and barium-doped materials, in combination with the previously discovered Abma --> P4(2)/ncm structural phase-transition in La(1.88)B(0.12)CuO(4), suggests that an electronic contribution to the lattice instability is present and maximizes at approximately 1/8 hole per copper atom. These observations indicate a dose connection between hole doping of the Cu-O sheets, tilting instabilities of the CuO(6) octahedra, and superconductivity in La(2)CuO(4)-based superconductors.     

CuFe2O4纳米微粒及其自形成磁性液体的磁性研究

对用其沉淀法制备的CuFe2O4磁性纳米微粒及其合成的自形成磁性液体在室温下进行磁性测量.其结果表明CuFe2O4微粒的饱和磁化强度较小,粉末与自形成磁性液体均呈超顺磁性-无剩磁、无矫顽力.用Langevin理论对测得的磁性进行了对比分析,从微粒间的相互作用解释了粉末和磁性液体的实测磁化曲线与Langevin理论的不同偏离现象.     

Superconductivity at 40 K in the Oxygen-Defect Perovskites La2-xSrxCuO4-y

Structural, magnetic, and electronic properties of compounds in the series La2-xSrx CuO4-y for 0.05 相似文献   

超导高梯度磁分离造纸厂污水处理

分析了超导高梯度磁分离污水处理技术的基本原理,介绍了超导高梯度磁分离技术在纸厂污水处理中的应用及设备,讨论了利用等离子体聚合薄膜制备具有强捕捉能力磁性粒子的工艺.

Abstract：

Superconducting magnetic separation is a new candidate method for purifying wastewater produced by paper factories owing to its compactness in volume and effectiveness in treatment. In this paper,the principles of wastewater purification with superconducting high gradient magnetic separation are analyzed, its usage and equipment in wastewater purifying factories are presented and the process of preparation of the magnetic particles having high scavenging capabilities with plasma polymerization polymer thin film is described.     

自形成MnFe2O4磁性液体的磁性研究

采用共沉淀法制备MnFe2O4磁性纳米微粒,并配制自形成磁性液体.测量了微粒粒径,以及MnFe2O4磁性纳米微粒、自形成磁性液体的磁性.磁性液体呈现出微粒所具有的矫顽力,其比饱和磁化强度与剩余磁化强度之比都是3∶1的关系.在高场下的磁化性质随v变化.通过分析得出自形成MnFe2O4磁性液体的磁性除与微粒磁性、微粒体积分数v以及基液磁性有关外,还受微粒表面非磁性层的影响.     

自形成MnFe2O4磁性液体的磁性研究

采用共沉淀法制备MnFe2O4磁性纳米微粒,并配制自形成磁性液体．测量了微粒粒径,以及MnFe2O4磁性纳米微粒、自形成磁性液体的磁性．磁性液体呈现出微粒所具有的矫顽力,其比饱和磁化强度与剩余磁化强度之比都是3：1的关系．在高场下的磁化性质随声。变化．通过分析得出自形成MnFe2O4磁性液体的磁性除与微粒磁性、微粒体积分数Фv 以及基液磁性有关外,还受微粒表面非磁性层的影响．     

Superconductivity in SrCuO2-BaCuO2 Superlattices: Formation of Artificially Layered Superconducting Materials

Pulsed-laser deposition was used to synthesize artificially layered high-temperature superconductors. Thin-film compounds were formed when the constraint of epitaxy was used to stabilize SrCuO(2)-BaCuO(2) superlattices in the infinite layer structure. Using this approach, two new structural families, Ba(2)Srn-1,Cun+1 O2n+2+delta and Ba(4)Srn-1 Cun+3O2n+6+delta have been synthesized; these families superconduct at temperatures as high as 70 kelvin.     

WO3复合La2/3Ca1/3MnO3的磁电阻效应与导电行为研究

采用溶胶-凝胶法制备了不同摩尔比的WO3复合La2/3Ca1/3MnO3(LCMO)样品,探讨了零场下LCMO样品的阻温关系及在不同磁场下的磁电阻效应.分析了体系在高温区和低温区的导电行为,并在此基础上讨论了磁场对导电机制的影响及起因.     

Temperature Dependence of the Superconducting Gap Anisotropy in Bi2Sr2CaCu2O8+x

Detailed data on the momentum-resolved temperature dependence of the superconducting gap of Bi(2)Sr(2)CaCu(2)O(8+x) are presented, complemented by similar data on the intensity of the photoemission superconducting condensate spectral area. The gap anisotropy between the Gamma-Mand Gamma-X directions increases markedly with increasing temperature, contrary to what happens for conventional anisotropic-gap superconductors, such as lead. Specifically, the size of the superconducting gap along the Gamma-X direction decreases to values indistinguishable from zero at temperatures for which the gap retains virtually full value along the Gamma-M direction. These data rule out the simplest type of d-wave order parameter.