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本文解释了La2CuO4+δ(0≤δ≤0.09)和La2-xSrxCuO4(0≤x≤0.3)两种p型系统含铜稀土氧化物中的电阻和Seebeck系数与温度的依赖关系,在室温以上,一氧大气压下的La2CuO4+δ系统趋于失氧;在500 K以上,超导样品显示出失氧的一级相变,并且恢复到反铁磁相。在转变温度T1≈300 K以下,对0<δ<0.05成份的样品,相分离成反铁磁相和超导相;而在Tcρ≈100 K的温度范围内,超导相进一步分离成富空穴和贫空穴畴。在0.04≤δ≤0.09范围内,Tc处的电阻陡降出现了台阶;我们认为,它反映了电子成对的起伏。在La2-xSrxCuO4系统中,对于成分为01≈300 K以上,空穴的运动是弥散的,但是ΔHm=0;而对于x≥0.22的样品,经历了从平滑到Fermi液态的转变。成份为0c1范围(其中空穴继续以弥散方式运动)是亚稳的,但是,在Tcρ≤150 K范围,出现了电荷起伏。当样品冷却通过T1时,对于成份为0.15≤x≤0.2的样品,经历了由弥散到强质量增强巡游电子状态的转变;在Tc处,从均匀的修饰电子的正常态凝聚成超导的载流子对。在超导成份样品的正常态中,不寻常的电子-晶格相互作用,可以归结为在CuO2面上从更离子性的到共价性的Cu:3dx2-r2─O:Pσ键合的转变;通过这种转变,轨道杂化和Hubbard U参量随Cu─O键长和Cu原子上的外表局域氧化态都产生灵敏的变化。 相似文献
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LIU Qing-Qing WANG Fu-Ren LI Feng-Ying CHEN Liang-Chen YU Ri-Cheng JIN Chang-Qing LI Yan-Chun LIU Jing 《中国物理快报》2008,25(6):2239-2241
A single-phase Sr2CuO3+δ superconductor is synthesized under high temperature and high pressure, in which oxygen atoms only partially occupy the apical sites next to the CuO2 planes and act as hole-dopants. Thesuperconducting transition temperature with Tcmax=75K is achieved in the material. Structure analysis from x-ray powder diffraction data show that this material crystallizes into a K2NiF4 structure with tetragonal unit cell of a=3.795(3)AAand c= 12.507(1)AA. Energy-dispersive synchrotron x-ray-diffraction studies at ambient are performed on powder samples of Sr2CuO3+δ in a diamond-anvil cell at pressure up to 35GPa. Anisotropic compressibility is found. Pressure-induced isostructural phase transition might exist as revealed by the discontinuous change of crystal cell volume V withpressure. 相似文献
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EFFECT OF THE SUBSTITUTION OF Ga AND Sn FOR Cu ON THE ELECTRONIC STRUCTURE AND SUPERCONDUCTIVITY OF La1.85Sr0.15CuO4 下载免费PDF全文
The electronic structure of La1.85Sr0.15CuO4, as well as the two cases of substitution of Ga and Sn for Cu, has been studied by the recursion method. The change of hole concentration and the effective local magnetic moment have also been calculated. Our calculations show that Ga and Sn destroy the two-dimensional character of the CuO2 plane and lead to the disorder of the electronic structure, accompanied by the migration of electrons which canines the decrease of the hole concentration in the CuO2 planes. From our point of view, these changes may be responsible for the destruction of superconductivity of the Ga and Sn-doped systems. 相似文献
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用高温高压法、在1 260 ℃和5.0 GPa条件下,成功制备出电子型掺杂层状钙钛矿结构锰氧化物La2-2xCa1+2xMn2O7(x=1.0~0.8)系列样品。样品的粉末X射线衍射实验和Rietveld精修结构分析表明,所制样品具有Sr3Ti2O7型四方结构,空间群为I4/mmm。随着电子浓度的增加,MnO6八面体畸变程度增大,晶胞体积增加。同时样品的磁化强度随La的掺入、x的增加而增强,反铁磁有序温度TN提高。由于双交换作用减小,样品的电阻增加。在测量温度范围内,没有观测到磁电阻效应。 相似文献
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本文采用超高氧压2.3 GPa合成方法,得到超导相含量大于30%的超导化合物La2CuO4+δ所采用的压力是目前所见报导中对La2CuO4化合物施加的最高氧压。湿化学方法测量给出过量氧含量δ=0.05±0.01,而TGA(氮气中)给出δ=0.143。高氧压合成产物经在空气中、不同温度下加热,然后淬火到室温,结果发现超导体在200~300 ℃的加热处理中存在着一个一级相变。经此相变后,超导体转变成反铁磁半导体。TGA及DSC证实了此相变的存在。该相变前后所联系的氧含量变化恰好为湿化学方法给出的结果,这部分与超导电性存在联系的过量氧,实际上引起了Cu2+向Cu(2+2δ)+的转变。该结果强有力地排除了所谓“超氧化物”引起超导电性的可能性。 相似文献
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采用热压法获得了具有不同混合比例的超导氧化物La1.85Sr0.15CuO4/超高分子量聚乙烯导电复合材料,并利用x射线衍射、扫描电子显微镜和标准四引线方法对复合材料的结构和低温电输运性质进行测量.实验结果显示,超导氧化物La1.85Sr0.15CuO4颗粒随机分布在聚合物本体中,相互间没有连接构成网络结构.在正常态下,复合材料的电阻-温度变化曲线给出类半导体行为.但对应于超导氧化物La1.85Sr0.15CuO4的超导转变温度Tc处,复合材料的电阻-温度变化曲线出现了极小值.室温下电阻率ρ随外加电场强度E的变化曲线测量结果表明,ρ-E曲线为一线形关系,随着电场强度E增加,电阻率ρ下降.文中对可能存在的导电机制进行分析,结果表明隧道贯穿模型可以很好地解释复合材料的导电机制.另外,外加电场强度E对复合材料的电输运特性有明显的影响. 相似文献
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Il Nuovo Cimento D - The temperature dependence of local Cu site conformations in single-domain crystals of Bi2Sr2CaCu2O8+y (Bi-2212) and La1.85Sr0.15CuO4 (La-214) has been determined by EXAFS... 相似文献
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The effect of disorder on the superconducting transition temperature T(c) of cuprate superconductors is examined. Disorder is introduced into the cation sites in the plane adjacent to the CuO2 planes of two single-layer systems, Bi(2.0)Sr(1.6)Ln(0.4)CuO(6+delta) and La(1.85-y)Nd(y)Sr0.15CuO4. Disorder is controlled by changing rare earth (Ln) ions with a different ionic radius in the former, and by varying the Nd content in the latter with the doped carrier density kept constant. We show that this type of disorder works as weak scatterers in contrast to the in-plane disorder produced by Zn, but remarkably reduces T(c), suggesting novel effects of disorder on high-T(c) superconductivity. 相似文献
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Dual nature of the electronic structure of (La(2--x--y)Nd(y)Sr(x))CuO(4) and La(1.85)Sr(0.15)CuO(4).
X J Zhou T Yoshida S A Kellar P V Bogdanov E D Lu A Lanzara M Nakamura T Noda T Kakeshita H Eisaki S Uchida A Fujimori Z Hussain Z X Shen 《Physical review letters》2001,86(24):5578-5581
High resolution angle-resolved photoemission measurements have been carried out on (La(1.4--x)-Nd(0.6)Sr(x))CuO(4), a model system with static one-dimensional (1D) charge ordering (stripe), and (La(1.85)-Sr(0.15))CuO(4), a high temperature superconductor (T(c) = 40 K) with possible dynamic stripes. In addition to the straight segments near ( pi,0) and ( 0,pi) antinodal regions, we have identified the existence of spectral weight along the [1,1] nodal direction in the electronic structure of both systems. This observation of nodal state, together with the straight segments near antinodal regions, reveals the dual nature of the electronic structure of stripes due to the competition of order and disorder. 相似文献
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The normal-state single particle spectral function of the high temperature superconducting cuprates, measured by the angle-resolved photoelectron spectroscopy (ARPES), has been considered both anomalous and crucial to understand. Here, we report an unprecedented success of the new extremely correlated Fermi liquid theory by one of us [B. S. Shastry, Phys. Rev. Lett. 107, 056403 (2011)] to describe both laser and conventional synchrotron ARPES data (nodal cut at optimal doping) on Bi(2)Sr(2)CaCu(2)O(8+δ) and synchrotron data on La(1.85)Sr(0.15)CuO(4). It fits all data sets with the same physical parameter values, satisfies the particle sum rule and successfully addresses two widely discussed kink anomalies in the dispersion. 相似文献
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We performed high-resolution angle-resolved photoemission spectroscopy on La1.85Sr0.15CuO4 to study the nature of the single-particle excitation gap. We found that there is a well-defined superconducting coherence peak in the off-nodal region while it is strongly suppressed around the antinode. The momentum dependence of the single-particle excitation gap shows a striking deviation from the dx-y2--wave symmetry with anomalous enhancement around the antinode in both the superconducting and the pseudogap state. The observed close correlation between the superconducting coherence peak and the pseudogap suggests a substantial contribution of the pseudogap to the anomalous behavior of the gap in the superconducting state. 相似文献
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Gadermaier C Alexandrov AS Kabanov VV Kusar P Mertelj T Yao X Manzoni C Brida D Cerullo G Mihailovic D 《Physical review letters》2010,105(25):257001
We determined electronic relaxation times via pump-probe optical spectroscopy using sub-15 fs pulses for the normal state of two different cuprate superconductors. We show that the primary relaxation process is the electron-phonon interaction and extract a measure of its strength, the second moment of the Eliashberg function λ[ω2] = 800 ± 200 meV2 for La(1.85)Sr(0.15)CuO4 and λ[ω2] = 400 ± 100 meV2 for YBa(2)Cu(3)O(6.5). These values suggest a possible fundamental role of the electron-phonon interaction in the superconducting pairing mechanism. 相似文献
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Karpinska K Cieplak MZ Guha S Malinowski A Skoskiewicz T Plesiewicz W Berkowski M Boyce B Lemberger TR Lindenfeld P 《Physical review letters》2000,84(1):155-158
Measurements of the resistivity, magnetoresistance, and penetration depth were made on films of La1.85Sr0.15CuO4, with up to 12 at. % of Zn substituted for the Cu. The results show that the quadratic temperature dependence of the inverse square of the penetration depth, indicative of d-wave superconductivity, is not affected by doping. The suppression of superconductivity leads to a metallic nonsuperconducting phase, as expected for a pairing mechanism related to spin fluctuations. The metal-insulator transition occurs in the vicinity of k(F)l approximately 1, and appears to be disorder driven, with the carrier concentration unaffected by doping. 相似文献
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Orgad D Kivelson SA Carlson EW Emery VJ Zhou XJ Shen ZX 《Physical review letters》2001,86(19):4362-4365
In the normal state of the high temperature superconductors Bi(2)Sr(2)CaCu(2)O(8+delta) and La2(-x)Sr(x)CuO4, and in the related "stripe ordered" material, La(1.25)Nd(0.6)Sr(0.15)CuO4, there is sharp structure in the measured single hole spectral function, A<(k-->,omega), considered as a function of k--> at fixed small binding energy omega. At the same time, as a function of omega at fixed k--> on much of the putative Fermi surface, any structure in A<(k-->,omega), other than the Fermi cutoff, is very broad. This is characteristic of the situation in which there are no stable excitations with the quantum numbers of the electron, as is the case in the one-dimensional electron gas. 相似文献
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The c-axis far-infrared reflectivity spectra in the superconducting state were investigated for La1.85-yNd(y)Sr0.15CuO4. The Josephson plasma edge rapidly shifts towards lower frequency with increasing y, and almost disappears when y exceeds a critical value ( y(c) approximately 0.12) above which the low-temperature-tetragonal (LTT) deformation switches on, stabilizing the spin/charge ordered stripe phase. In the vicinity of y(c), a "normal state" reentrant behavior was observed with lowering temperature below Tc. This clearly demonstrates that the static stripe order pinned by the LTT distortion suppresses the interlayer phase coherence. 相似文献