Electron-phonon coupling reflecting dynamic charge inhomogeneity in copper oxide superconductors

The attempt to understand copper oxide superconductors is complicated by the presence of multiple strong interactions in these systems. Many believe that antiferromagnetism is important for superconductivity, but there has been renewed interest in the possible role of electron-lattice coupling. The conventional superconductor MgB2 has a very strong electron-lattice coupling, involving a particular vibrational mode (phonon) that was predicted by standard theory and confirmed quantitatively by experiment. Here we present inelastic scattering measurements that show a similarly strong anomaly in the Cu-O bond-stretching phonon in the copper oxide superconductors La(2-x)Sr(x)CuO4 (with x = 0.07, 0.15). Conventional theory does not predict such behaviour. The anomaly is strongest in La(1.875)Ba(0.125)CuO4 and La(1.48)Nd(0.4)Sr(0.12)CuO4, compounds that exhibit spatially modulated charge and magnetic order, often called stripe order; it occurs at a wave vector corresponding to the charge order. These results suggest that this giant electron-phonon anomaly, which is absent in undoped and over-doped non-superconductors, is associated with charge inhomogeneity. It follows that electron-phonon coupling may be important to our understanding of superconductivity, although its contribution is likely to be indirect.     

Link between spin fluctuations and electron pairing in copper oxide superconductors

Although it is generally accepted that superconductivity is unconventional in the high-transition-temperature copper oxides, the relative importance of phenomena such as spin and charge (stripe) order, superconductivity fluctuations, proximity to a Mott insulator, a pseudogap phase and quantum criticality are still a matter of debate. In electron-doped copper oxides, the absence of an anomalous pseudogap phase in the underdoped region of the phase diagram and weaker electron correlations suggest that Mott physics and other unidentified competing orders are less relevant and that antiferromagnetic spin fluctuations are the dominant feature. Here we report a study of magnetotransport in thin films of the electron-doped copper oxide La(2?-?x)Ce(x)CuO(4). We show that a scattering rate that is linearly dependent on temperature--a key feature of the anomalous normal state properties of the copper oxides--is correlated with the electron pairing. We also show that an envelope of such scattering surrounds the superconducting phase, surviving to zero temperature when superconductivity is suppressed by magnetic fields. Comparison with similar behaviour found in organic superconductors strongly suggests that the linear dependence on temperature of the resistivity in the electron-doped copper oxides is caused by spin-fluctuation scattering.     

铜氧化物高温超导体的晶体结构和物理性能研究

阐述了铜氧化物高温超导体的晶体结构 ,指出导电区、蓄电区的划分和电子相图是铜氧化物高温超导体重要的共性特征 .介绍了分块模型及其在研究晶体结合能、弹性模量中的应用 ,对铜氧化物高温超导体结构和性能之间的关系作了探讨 .最后对当前高温超导体研究的几个热点问题及其应用前景予以简介 .     

Small phonon contribution to the photoemission kink in the copper oxide superconductors

Despite over two decades of intense research efforts, the origin of high-temperature superconductivity in the copper oxides remains elusive. Angle-resolved photoemission spectroscopy experiments have revealed a kink in the dispersion relations (energy versus wavevector) of electronic states in the copper oxides at binding energies of 50-80 meV, raising the hope that this anomaly could be a key to understanding high-temperature superconductivity. The kink is often interpreted in terms of interactions between the electrons and a bosonic field. Although there is no consensus on the nature of the bosons (or even whether a boson model is appropriate), both phonons and spin fluctuations have been proposed as possible candidates. Here we report first-principles calculations of the role of phonons and the electron-phonon interaction in the photoemission spectra of La(2 - x)Sr(x)CuO4. Our calculations within the standard formalism demonstrate that the phonon-induced renormalization of the electron energies and the Fermi velocity is almost one order of magnitude smaller than the effect observed in photoemission experiments. Therefore, our result rules out electron-phonon interaction in bulk La(2 - x)Sr(x)CuO4 as the exclusive origin of the measured kink. Our conclusions are consistent with those reached independently in a recent study of the related compound YBa2Cu3O7.     

An explanation for a universality of transition temperatures in families of copper oxide superconductors

A remarkable mystery of the copper oxide high-transition-temperature (T(c)) superconductors is the dependence of T(c) on the number of CuO2 layers, n, in the unit cell of a crystal. In a given family of these superconductors, T(c) rises with the number of layers, reaching a peak at n = 3, and then declines: the result is a bell-shaped curve. Despite the ubiquity of this phenomenon, it is still poorly understood and attention has instead been mainly focused on the properties of a single CuO2 plane. Here we show that the quantum tunnelling of Cooper pairs between the layers simply and naturally explains the experimental results, when combined with the recently quantified charge imbalance of the layers and the latest notion of a competing order nucleated by this charge imbalance that suppresses superconductivity. We calculate the bell-shaped curve and show that, if materials can be engineered so as to minimize the charge imbalance as n increases, T(c) can be raised further.     

Copper oxide superconductors: sharp-mode coupling in high-Tc superconductors

In conventional superconductivity, sharp phonon modes (oscillations in the crystal lattice) are exchanged between electrons within a Cooper pair, enabling superconductivity. A critical question in the study of copper oxides with high critical transition temperature (Tc) is whether such sharp modes (which may be more general, including, for example, magnetic oscillations) also play a critical role in the pairing and hence the superconductivity. Hwang et al. report evidence that sharp modes (either phononic or magnetic in origin) are not important for superconductivity in these materials, but we show here that their conclusions are undermined by the insensitivity of their experiment to a crucial physical effect.     

Zn元素在高TC氧化物超导体中的作用

元素替代效应是研究高TC氧化物超导体的电子结构、晶体结构变化及宏观物性间相互关联、相互制约的重要途径,是获得高TC超导氧化物的重要手段。本文就高TC氧化物超导体中的Zn元素替代效应,尤其对Y系、Bi系高TC氧化物超导体的CuO2平面上Cu(2)位部分取代,导致TC被强烈抑制的机理进行了分析研究,讨论了从中给出的有关高温氧化物超导电性微观机制的信息。     

高T_c铜氧化物超导体的低密度载流子特征

用电负性均衡原理研究在高Tc铜氧化物超导体中由于元素中有化学键的形成,形成了低密度载流子浓度并对超导电性产生了强烈的影响;由于元素之间形成化学键,电子密度的分布在超导材料中的不均匀性,使得超导材料中形成宏观物理性质不同的板块结构。     

Non-quantized penetration of magnetic field in the vortex state of superconductors

As first pointed out by Bardeen and Ginzburg in the early sixties, the amount of magnetic flux carried by vortices in superconducting materials depends on their distance from the sample edge, and can be smaller than one flux quantum, phi0 = h/2e (where h is Planck's constant and e is the electronic charge). In bulk superconductors, this reduction of flux becomes negligible at submicrometre distances from the edge, but in thin films the effect may survive much farther into the material. But the effect has not been observed experimentally, and it is often assumed that magnetic field enters type II superconductors in units of phi0. Here we measure the amount of flux introduced by individual vortices in a superconducting film, finding that the flux always differs substantially from phi0. We have observed vortices that carry as little as 0.001phi0, as well as 'negative vortices', whose penetration leads to the expulsion of magnetic field. We distinguish two phenomena responsible for non-quantized flux penetration: the finite-size effect and a nonlinear screening of the magnetic field due to the presence of a surface barrier. The latter effect has not been considered previously, but is likely to cause non-quantized penetration in most cases.     

铜纳米粒子的电化学制备及其氧化物的光电催化分解水性能

以五水硫酸铜(CuSO4·5H2O)为前驱体,聚乙烯吡咯烷酮(PVP)为包裹剂,在水溶液中采用电化学方法在氧化铟锡( ITO)表面制备得到了形貌和尺寸均一的铜纳米粒子,并研究了前躯体的浓度、包裹剂的种类和浓度以及电化学沉积电位对产物的形貌和生长密度的影响。将得到的产物经过热处理后,会在表面生成一层黑色的氧化铜,经过测试发现其对光电分解水制氢具有良好的催化作用。     

Bioleaching of copper oxide ore by Pseudomonas aeruginosa

Bioleaching is an environmentally friendly method for extraction of metal from ores. In this study, bioleaching of copper oxide ore by Pseudomonas aeruginosa was investigated. Pseudomonas aeruginosa is a heterotrophic bactermm that can produce various organic acids in an appropriate culture medium, and these acids can operate as leaching agents. The parameters, such as particle size, glucose percentage in the culture medium, bioleaching time, and solid/liquid ratio were optimized. Optimum bioleaching conditions were found as follows： particle size of 150-177 μm, glucose percentage of 6%, bioleaching time of 8 d, and solid/liquid ratio of 1：80. Under these conditions, 53% of copper was extracted.     

碱性氧化铜矿产氨菌浸出特性

为了研究碱性氧化铜矿产氨菌浸出特性,分析了产氨菌浸矿过程对矿石的作用.将云南某矿的碱性氧化铜矿置于含菌培养液、去菌培养液和氨水等5种浸矿溶液中,在同一条件下进行摇瓶浸矿实验,剖析溶液中各可能的浸矿因子.研究结果表明:产氨菌产氨能力较强,尿素培养液中氨质量浓度最大达8.93 g·L-1;产氨量与细菌含量呈正相关关系,细菌含量越高,产氨量越大;产氨菌主要通过产氨间接浸矿,此外产氨菌和其代谢产物都能直接作用于矿石,浸矿能力细菌产氨>细菌>细菌代谢产物,三者比值约为12:5:4.     

多次电火花线切割换向条纹形成机理分析

针对高速电火花多次切割表面容易出现换向条纹问题,首先从应变能角度,分析了电极丝因蠕变松弛而导致其张紧力的变化规律,然后基于目前普遍采用的单边重锤张力控制技术,建立了电火花线切割运丝系统张紧力数学模型,根据多次切割单边偏移量与张紧力的关系,分析出工件表面换向条纹产生机理,在此基础上,提出了通过控制张紧力来消除换向条纹的观点,为降低多次切割加工表面粗糙度值提供基础理论依据。     

磁性氧化铁纳米线的制备与表征

通过溶胶-凝胶法在氧化铝模板（AAO）中制备出了磁性Fe_2O_3纳米线阵列,然后去除AAO模板得到磁性Fe_2O_3纳米线。用SEM,TEM,FTIR,EDX,VSM对磁性纳米线的形貌、微结构和磁性能进行表征。SEM和TEM结果显示磁性纳米线的直径约为50～80nm,长度在8～10μm,长径比为120～180;FTIR和EDX结果表明制备的产物是磁性Fe_2O_3纳米线;VSM结果表明磁性氧化铁纳米线阵列存在明显的磁各向异性。此外,采用Zeta电位仪对磁性Fe_2O_3纳米线表面的电性进行了研究,结果表明纳米线表面带正电荷,有利于和动物细胞相结合。     

量子线与量子点中的量子态

本文简要地介绍了量子线与量子点的概念，并说明可利用电容测量研究低维系统的性质。     

含碳酸盐脉石氧化铜矿的酸浸动力学

针对碳酸盐脉石对氧化铜矿酸浸动力学的影响进行探讨,研究了温度、酸度、矿石粒径、液固质量比、振荡速度等因素对含碳酸盐脉石氧化铜矿浸出的影响.结果表明,高温、高酸度、高液固质量比、小粒径和高振荡速度利于矿石的浸出,但碳酸盐脉石使得酸耗增加.考虑浸出成本确定合理的浸出条件为温度303 K、酸度35 g·L-1、矿石粒径0.074~0.125 mm、液固质量比3﹕1以及振荡速度180 r·min-1,浸出180 min后铜浸出率达53.6%.对浸出前后矿石表面形貌进行分析.结果显示碳酸盐脉石与酸反应后在矿石表面形成CaSO4·2H2 O沉淀,覆盖在颗粒表面,限制了矿石颗粒孔裂隙的发育.基于收缩未反应核模型对浸出动力学进行分析,发现碳酸盐脉石反应生成的沉淀阻碍了浸出反应,固体产物层扩散为浸出反应的控制步骤,反应的表观活化能为8.65 kJ·mol-1.     

Cu、O同位素效应与高Tc超导体超导电性机理

Cu元素、O元素在铜氧化物高Tc超导体中对超导电性的产生,超导转变温度的变化,掺杂元素的特征效应具有决定性作用。对Cu元素、O元素的性质特征认识,成键特点,以及在铜氧化物高Tc超导体中的同位素效应清楚的理解,对全面揭示高Tc铜氧化物超导体超导电性机理具有关键作用。通过分析Cu元素、O元素在铜氧化物超导体中的同位素效应,得出了高Tc铜氧化物超导电性的机理仍是电声机制,CuO2平面上的Cu元素,O元素的声子直接参于电声子配对,CuO2平面上的Cu、O元素的键态的声子模对电声配对具有决定性作用。     

弥散铜材料的高温本构方程

弥散铜是一种新型的粉末体电极材料 ,在加工制备过程中其变形行为会不同于致密体 .针对粉末体材料的变形特性 ,提出了弥散铜的高温本构方程的数学模型 ,并通过大量的热模拟压缩实验 ,确定了该材料高温本构方程的具体形式     

含铜取向硅钢磁性能波动成因分析

含铜取向硅钢是一种成本低、成品率高的新型CGO取向硅钢.其制备工艺明显区别于主流的低温加热渗氮高磁感(HiB)取向硅钢,其产品的磁性能波动范围显著高于低温渗氮钢.本文对实际生产中收集到的一些含铜CGO钢成品板中的组织与磁性能进行研究分析,尝试建立不同组织和磁性能相互间的对应关系,并对磁性能波动现象进行分析.分析结果表明,含铜CGO钢成品板组织与抑制剂有明确的对应关系,而晶粒尺寸与Goss晶粒取向度并不完全呈对应关系.同时对热轧板中的异常组织进行了深入研究,认为热轧板表层脱碳区和中心层粗大形变晶粒的存在,直接影响了抑制剂的分布,导致最终成品板中组织和磁性能的波动.     

重离子碰撞中量子源的电磁场研究

在计算真空中的超重力带电粒子在与粒子康普顿波长相距的距离所产生的电磁场时,粒子的波函数由克莱因—戈登方程控制。对于标量粒子、自旋半粒子或狄拉克方程,它们产生的电磁场在大小和方向上与库仑场有本质上的不同,这是由点电荷引起的量子扩散效应。因此,对重离子碰撞产生的电磁场的实际计算必须建立在对价夸克进行全量子处理的基础上。