薄膜厚度对La1.85Sr0.15CuO4薄膜结构和超导电性的影响

使用直流同轴磁控溅射法,在SrTiO3(STO)衬底上成功制备出c取向的La1.85Sr0.15CuO4(LSCO)超导薄膜.通过电输运测量系统和X射线衍射仪研究了薄膜厚度对LSCO(x＝0.15)薄膜电学性质和晶体结构的影响.实验证明随着膜厚增加,(006)衍射峰的半高宽(Full Width at Half Maximum,FWHM)逐渐减小,薄膜的取向性增强,与此同时,薄膜的超导转变温度TC逐渐提高.     

Mo低掺杂La_(0.67)Sr_(0.33)MnO_3的磁电特性及室温磁电阻增强(英文)

采用固相反应法成功制备了Mo低掺杂La0.67Sr0.33Mn1-xMoxOc(x=0,0.02)单相多晶样品,系统研究了样品的磁性、电输运特性和磁电阻效应.发现Mo低掺杂对La0.67Sr0.33MnO3 的居里温度影响很小,但在La0.67Sr0.33MnO3铁磁基态背景下诱导出团簇自旋玻璃态行为.在低温区(0.1相似文献   

La1-x／2Pr1-x／2SrxCuO4的电输运性质和超导电性

La1-x/2Pr1-x/2SrxCuOy(LPSCO)多晶样品采用传统的固相反应法制备.X射线衍射表明:LPSCO具有典型的空穴搀杂的T-214相的结构.磁化率测量显示:Sr搀杂在0.05≤x≤0.30范围内具有超导转变;Tc随x的增大呈抛物线形式变化,且在x=0.18时达到最大值28K.电阻的测量显示:随搀杂量的增大,系统呈现从绝缘到半导体,最后到金属的导电行为的变化;在欠掺杂区,正常态电阻温度关系符合ρ(T)=ρ0 αT-ClnT;而在过掺杂区,对数项消失.本文从替代所引起的晶体结构和载流子特性变化解释了Sr掺杂样品的电输运行为和超导特性.     

La2-xSrxCuO4单晶膜的热电势与电阻率

测量了高质量的单晶膜La2-xSrxCuO4(x=010,020,025)的电阻率和热电势.La19Sr01CuO4电阻率呈现S型行为,表明存在一个赝能隙,在赝能隙态可以用公式ρ=ρ0+βexp(-ΔT)很好地拟合.热电势的测量表明,在超导转变前样品的残余热电势值非常小,这是膜的高质量引起的,三个样品在200K以上都出现一个宽峰,对其进行了一些理论模型分析,并与电子型超导体热电势结果作了比较. 关键词： 薄膜 输运性质 热电势     

Sm2-xCexCuO4单晶的赝能隙行为研究

我们在电子型超导体Sm1.85Ce0.15CuO4中首次观察到赝能隙的证据.研究了在O2中不同退火时间,单晶Sm1.85Ce0.15CuO4样品的电阻率ρ和热电势S,电阻率ρ的测量结果显示退火后样品高温区电阻率ρ、dρ/dT和热电势的斜率dS/dT斜率增加,意味着载流子浓度下降,与减小Ce掺杂量x的作用等效.所有的样品S～T和ρ～T曲线在某个温度T*下都发生斜率的改变,该转变温度随着退火时间的增加而向高温区移动,而且越来越明显.这可能是因为该温度下赝能隙被打开,热电势曲线在某个温度下存在一个最小值,这是载流子局域化的表现;热电势曲线上50K附近观察到一个明显的声子曳引峰,正的峰值表示载流子符号在低温区发生了改变,即由高温的电子型变为低温的空穴型,与霍尔系数实验中斜率变化一致.     

La0.5Sm0.2Sr0.3MnO3/x（Sb2O3）体系电输运性质及MR温度稳定性

用固相反应法制备La0.5Sm0.2Sr0.3MnO3/x(Sb2O3)(x=0.00,0.02,0.04,0.05,0.075,0.10,0.15)系列样品,通过X射线衍射(XRD)谱、电阻率-温度(ρ～T)曲线、ρ～T拟合曲线、磁电阻-温度(MR～T)曲线,研究了该体系的电输运性质及MR的温度稳定性.所有样品的电输运性质都表现出绝缘体-金属相变,相变温度很高(312K)且基本保持不变,随Sb2O3复合量增大,电阻率迅速增大,类金属导电可以用ρ=ρ0+AT2公式拟合,表明导电机制是电子-电子相互作用,x=0.075的样品,在200～320K温区磁电阻基本保持不变,MR的温度稳定性是晶界引起的隧穿磁电阻与钙钛矿颗粒体相本征磁电阻竞争的结果.     

超导体Bi1.8Pb0.2Sr2-xLaxCuOy的电阻率和热电势研究

本文对名义组份为Bi1.8Pb0.2Sr2-xLaxCuOy系列样品的电阻率和热电势特性进行了实验研究.测量表明,Pb掺杂可以进一步提高超导转变温度Tc ;随着La含量的增加,Tc 按照典型的抛物线型规律变化;La掺杂极大地影响超导体正常态的输运特性.我们的分析指出,热电势在正常态所表现出的规律与高温超导机制密切相关,而且电阻率正常态输运特性的变化可用La掺杂造成CuO6八面体顶点氧发生位移来解释.     

电子型超导体Nd1.85Ce0.15CuO4单晶输运性质研究

我们测量了最佳掺杂的Nd1．85Ce0．15CuO4单晶的电阻率和ab面以及c方向热电势．ρ-T曲线在高温下表现为非常好的直线，超导转变比较尖锐Tc,mid=20．6K，说明我们的样品品质很好．低温下的电阻率拟合结果表明频率大约100K的软声子模与载流子有强烈相互作用，这是极化子模型有力的证据．对于热电势结果，令人惊奇的是，无论数值还是曲线形状，包括低温曳引峰的位置，c方向的热电势Sc与ab面内的热电势Sab非常接近．这可能是某种共同的机制导致的结果．比较Nd1．85Ce0．15CuO4和Sm1.85Ce0.15CuO4的热电势曲线可以发现，二的数值和曲线形状基本相同，而与La1．85Sr0．15CuO4差异较大，这进一步说明了顶点氧在这些体系中的作用．     

(La1-xSmx)0.185Sr0.15CuO4的输运性质的研究

通过对系列（La1-xSmx)0.185Sr0.15CuO4（x=0,0.05,0.10,0.15)的多晶样品在4.2K-300K的电阻率和液氮温区内的热电势的测量,发现（La1-xSmx)0.185Sr0.15CuO4的电阻率在高温区呈现出线性关系,其斜率也随着x的增大而增大,在x=0.10时达到最大,而在Tc到100K的温区,随着Sm含量的增加,则呈现出由金属行为到类半导体行为的转变,同时超导温度Tc也随着降低,液氮温区内的温差热电势反映了随着Sm含量的增加,体系的载流子浓度也随之降低。     

Ag和K掺杂对La4/5Sr1/5MnO3电输运性质及磁电阻的影响

用固相反应法制备La4/5Sr1/5MnO3及在其A位分别掺K、Ag系列样品,通过X射线衍射(XRD)谱,电阻率-温度(ρ～T)曲线,磁电阻-温度(MR～T)曲线,研究了在A位同时掺入一价、二价元素而保持Mn3+/Mn4+比值(摩尔比n(A)/n(B))不变的钙钛矿锰氧化物体系A位离子半径及A位离子的无序度σ2对电输运性质及磁电阻的影响.结果表明:A位离子的无序度σ2对电输运性质的影响比A位平均离子半径对电输运性质的影响大;电阻率曲线出现双峰是由于表面相电阻率与体相电阻率竞争的结果;MR的温度稳定性是本征磁电阻与隧穿磁电阻竞争的结果;掺K样品在253～175K温区MR从8.1%缓慢上升到9.5%,掺Ag样品在260K以下温区MR都在7.4%以上,纯的La4/5Sr1/5MnO3样品在318～259K温区MR都在7.0%以上,在如此宽温区MR几乎不变有利于MR的实际应用.     

一些高Tc超导体的弹性性质

 本文用超声相比较方法测定了高T_c超导体La_1.85Sr_0.15CuO₄，La₂CuO₄和YBa₂Cu₃O₇的纵波和横波声速，进而导出了它们的纵向模量、切变模量、杨氏模量、泊松比、德拜温度及定体比热。在La_1.85Sr_0.15CuO₄样品上，还进行了压力实验，发现所有弹性模量都是随压强增加而增加。定体比热c_V和泊松比σ在高压下则略有下降。德拜温度是随压强增加而增加的。     

La2-xBaxCuO4单晶反常的正常态输运性质研究

测量了La2-xBaxCuO4系列单晶样品的电阻率和热电势,我们发现,当＝0．125（x＝1／8）时,La2-xBaxCuO4的截流子是所有样品中局域化最强的,但数据分析结果显示,它又是弱域化行为,文中我们讨论了Tc的被压制的原因,得出这可能与低温下LTO到LTT的结构相变,空穴与自旋的静态条纹有序有关,热电势结果观察不到任何声子曳引的痕迹,表明在LBCO体系中电声子的相互作用很弱。     

High critical temperature by resonant quantum confinement: Evidence for polarons ordering at T *≈1.5T c in Bi-2212 and La-214 by EXAFS

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...     

Metallic nonsuperconducting phase and D-wave superconductivity in Zn-substituted La1.85Sr0.15CuO4

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.     

Extremely correlated Fermi-liquid description of normal-state ARPES in cuprates

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.     

Effect of disorder outside the CuO2 planes on Tc of copper oxide superconductors

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.     

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).

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.     

c-axis optical response in the static stripe ordered phase of the cuprates

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.     

Nd1.67Sr0.33NiO4中的热导反常

报道了两个典型掺杂的镍氧化物Nd＿2-xSr＿xNiO＿4(x =0.33,1.35)的低温热导率、电阻率和低场交流磁化率，测试温区为77—300K. 在Nd＿2-xSr＿xNiO＿4 (x=0.33)样品的热导率-温度曲线上在电荷有序转 变温度（T＿CO）和自旋有序转变温度（T＿SO）附近分别观测到反常， 电荷有序使热导率在T＿CO以下有所增加，反铁磁自旋有序使热导率在T＿SO附近被压制. 在低场交流磁化率-温度曲线上也分别观测到对电荷有序和自旋有 序的响应，而在其电阻率-温度曲线上仅观测到电荷有序. 作为比较，Nd＿1.67Sr0.33NiO＿4样品中没有观测到输运性质和磁性质上的反常. 两个样品中声子热导占 主导地位. Nd＿1.67Sr0.33NiO＿4样品中电荷有序和自旋有序导致的热导 率的反常表明样品中存在强的电荷-声子和自旋-声子相互作用. 关键词： 热导率 电荷有序 自旋有序     

Evidence of electron fractionalization from photoemission spectra in the high temperature superconductors

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.