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1.
T'-214相化合物R2-xCexCuO4(R为稀土离子)成为超导体决定于R3+的离子半径大小、Ce4+的取代量和化合物的热处理时的稳定性.从Raman光谱实验结果提出热处理过程中发生电荷转移.Ce4+的取代引起TN(Cu)下降,当TN(Cu)降到0时,超导性出现。不同的稀土离子TN(Cu)不同,稀土离子的反铁磁性(AFM)与超导性(SC)共存。热电势的测量结果可以用双通道模型解释,n型超导体中电子与空穴共存. 相似文献
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We present a review of photoexcited quasiparticle dynamics of cuprate and pnictide high‐temperature superconductors in regimes (temperature, doping) where different phases such as superconductivity, spin‐density‐wave (SDW) and pseudogap phases coexist or compete with one another. We start with the overdoped cuprate superconductor Y1–xCax Ba2Cu3O7–δ, where the superconducting gap and pseudogap coexist in the superconducting state. In another cuprate Tl2Ba2Ca2Cu3Oy, we ob‐ serve a competition between SDW and superconducting orders deep in the superconducting state. Finally, in the underdoped iron pnictide superconductor (Ba,K)Fe2As2, SDW order forms at 85 K, followed by superconductivity at 28 K. We also find the emergence of a normal‐state order that suppresses SDW at a temperature T * ~ 60 K and argue that this normal‐state order is a precursor to superconductivity. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
铜氧化物高温超导体的发现, 打破了基于电声子相互作用BCS理论所预言的超导转变温度极限, 掀开了高温超导材料探索和高温超导机理研究的序幕. 根据掺杂类型的不同, 铜氧化物超导材料可以分为空穴型掺杂和电子型掺杂两类. 受限于样品, 对电子型掺杂铜氧化物的研究工作远少于空穴型掺杂体系. 本文简要回顾有关电子型掺杂铜氧化物超导体近期研究成果, 通过对比电子型掺杂和空穴型掺杂铜氧化物的相图来阐明电子型掺杂铜氧化物的研究对探索高温超导机理的必要性, 并特别针对电子型掺杂样品制备中的关键因素“退火过程”展开讨论. 结合课题组最新实验结果和相关实验报道我们发现电子型掺杂铜氧化物超导体在制备过程中除受到温度和氧分压的影响外, 退火效果还受到界面应力的强烈调制. 在综合考虑样品生长过程中温度、气氛及应力等多种因素的基础上, 探讨了“保护退火”方法导致电子型体系化学掺杂相图变化的起因. 相似文献
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ψ=ψ0eiφ行为用统一的波函数进行描述,其相位φ在宏观尺度上是相同的.当磁场低于一定值的时候,在超Φ0=h/2e保证最大的界面面积,降低系统能量.该最小的磁通束被称为磁通量子,其磁通量是(h为普朗克超导态是一个宏观量子相干态,其载流子是库珀对.在没有外加磁场和电流的时候,这些库珀对的运动导体的边界处穿透深度内会出现一... 相似文献
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Gd,-.Na.CuO#, an interesting compound with complex magnetic behavior, has beensynthesized by a PbO-based flux method (l) and a solid state reaction (2) at temperaturesabout 1000"C. Its X-ray diffraction pattern has been indexed with tetragonal latticeparameters (l,3). Here we report a low temperature synthetic route in which the newmonoclinic form of Gd,-.Na.CuO# is obtained directly by precipitation from a moltenKOH/NaOH/KNO, solution. The SEM, EDX, XRD, XPS and magnetic characte… 相似文献
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利用三维量子电动力学理论中的Dyson-Schwinger方程方法, 研究了零温情况下平面铜氧化合物超导体的反铁磁相和d波超导相之间的相变. 通过在朗道规范下近似解析求解和数值求解完全耦合的Dyson-Schwinger方程、并将所得结果与1/N展开方法的结果相比较, 发现在半填充准费密子味道数约小于等于4的情况下, 通过手征对称性自发破缺, d波超导相可以演化到反铁磁相, 并且反铁磁相有可能与d波超导相共存. 通过进一步比较不同相的压强, 还说明反铁磁与d波超导共存相为稳定相, 从而反铁磁相确实可以与d波超导相共存. 相似文献
8.
V. P. Glazkov B. N. Savenko V. A. Somenkov D. V. Sheptyakov S. Sh. Shilstein 《高压研究》2013,33(3-6):201-207
Abstract The crystal structure of Nd2CuO4 has been studied by neutron diffraction at pressure up to 5 Gpa. The volume compressibility value was determined as 5·6·10?3/Gpa. The decrease of positional parameter of neodymium at high pressure has been observed. This structural change is explained by pressure induced neodymium ions charge increase. 相似文献
9.
Electron-phonon coupling in cuprate and iron-based superconductors revealed by Raman scattering
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Electron-phonon coupling (EPC) in cuprate and iron-based superconducting systems, as revealed by Raman scat- tering, is briefly reviewed. We introduce how to extract the coupling information through phonon lineshape. Then we discuss the strength of EPC in different high-temperature superconductor (HTSC) systems and possible factors affecting the strength. A comparative study between Raman phonon theories and experiments allows us to gain insight into some crucial electronic properties, especially superconductivity. Finally, we summarize and compare EPC in the two existing HTSC systems, and discuss what role it may play in the HTSC. 相似文献
10.
High‐temperature superconductivity and long‐range order in strongly correlated electronic systems
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Lawrence J. Dunne 《International journal of quantum chemistry》2015,115(20):1443-1458
A selective review of the question of how repulsive electron correlations might give rise to off‐diagonal long‐range order (ODLRO) in high‐temperature superconductors is presented. The article makes detailed explanations of the relevance to superconductivity of reduced electronic density matrices and how these can be used to understand whether ODLRO might arise from Coulombic repulsions in strongly correlated electronic systems. Time‐reversed electron pairs on alternant Cuprate and the iron‐based pnictide and chalcogenide lattices may have a weak long‐range attractive tail and much stronger short‐range repulsive Coulomb interaction. The long‐range attractive tail may find its origin in one of the many suggested proposals for high‐Tc superconductivity and thus has an uncertain origin. A phenomenological Hamiltonian is invoked whose model parameters are obtained by fitting to experimental data. A detailed summary is given of the arguments that such interacting electrons can cooperate to produce a superconducting state in which time‐reversed pairs of electrons effectively avoid the repulsive hard‐core of the Coulomb interaction but reside on average in the attractive well of the long‐range potential. Thus, the pairing of electrons itself provides an enhanced screening mechanism. The alternant lattice structure is the key to achieving robust high‐temperature superconductivity with dx2‐y2 or sign alternating s‐wave or s± condensate symmetries in cuprates and iron‐based compounds. Some attention is also given to the question first raised by Leggett as to where the Coulombic energy is saved in the superconducting transition in cuprates. A mean‐field‐type model in which the condensate density serves as an order parameter is discussed. Many of the observed trends in the thermal properties of cuprate superconductors are reproduced giving strong support for the proposed model for high‐temperature superconductivity in such strongly correlated electronic systems. © 2015 Wiley Periodicals, Inc. 相似文献