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La_1.85Sr_0.15CuO₄(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 关键词： 1.85Sr_0.15CuO₄薄膜')" href="#">La_1.85Sr_0.15CuO₄薄膜 超导电性 晶体结构     

La1.85Sr0.15CuO4纳米线阵列的微结构与超导电性

采用溶胶-凝胶结合多孔氧化铝硬模板约束的方法,成功制备出直径约30nm的La1.85Sr0.15CuO4纳米线阵列,用XRD与X-ray EDX测定了所制备纳米线的物相与成分;FE-SEM与TEM表征了其形貌特征;由HRTEM与SAED测量分析了其微结构;磁化强度的测量结果表明样品具有Tc= 30 K的超导电性,比块材La1.85Sr0.15CuO4的Tc稍低.分析表明所制备的样品中存在一种a,b轴拉伸,c轴压缩的结构畸变,减弱了铜氧面内Cu3d和O2p轨道的杂化程度,减小了a,b面内的态密度,从而压制了体系的超导电性.     

Nd1.85Ce0.15 CuO4-δ单晶c-轴方向电阻的低场行为

采用自助熔剂缓冷法成功地生长出了Nd1.85Ce0.15CuO4-δ单晶,其零场下零电阻温度约为21K.在0-0.5T范围内分别测量了磁场平行和垂直样品表面的电阻转变曲线以及0.5T不同角度下的电阻转变曲线.结果显示磁场平行和垂直样品表面时的转变温度Tp随磁场的变化均服从H=H0(1-Tp(h)/Tp(0))2关系.0.5T不同角度下的转变温度Tp符合有效质量模型,即Tp∝H1/12(cos2θ+sin2θ/γ2)1/4.该单晶的各向异性因子γ约为45.     

电子型超导体Sm1.85Ce0.15CuO4单晶样品的制备和品质鉴定

本研究了助溶剂法生长了Sm2-xCeXCuO4单晶的可行性，制备出x=0.15,Sm2-x=CexCuO4单晶，并作了品质鉴定，为了研究坩埚中的Al掺入的情况，对电阻率和热电势进行了测量。     

不同退火条件下Nd1.85Ce0.15CuO4-δ单晶输运性质的研究

本文测量了电子型高温超导体Nd1.85Ce0.15 CuO4-δ单晶在不同退火条件下的ab面电阻率(ρ)和热电势(S).电阻率曲线偏离了费米液体理论T2的温度依赖关系和热电势在整个测量温区(15～300 K)都为正值表明在这一体系中有两种载流子共存.基于此,我们提出了一个空穴型窄带叠加在一个电子型宽带的双能带模型.进一步的退火处理实验表明:这一理论模型能很好的解释电阻率和热电势在不同退火条件下的行为,并有助于我们分析在不同退火过程中能带的结构和填充位置的变化.在深度去氧退火过程中,能带结构保持不变的但能带填充度增加使得费米能(EF)上升了;在加氧退火过程中EF位置不变而空穴型窄带变宽了.     

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．     

Zn,Ni,Mg高掺杂La1.85Sr0.15CuO4的晶体结构比较

对Zn,Ni,Mg高掺杂的La_1.85Sr_0.15CuO₄(LSCO)超导体的X射线衍射谱进行了仔细的分析,从而获得了各掺杂样品的晶格常量、原子结构参量及衍射的峰形参量,比较了不同掺杂所引起的晶体结构的差异,计算了由于掺杂所产生的晶格内部的微应变,结果表明非磁性金属Zn,Mg掺杂比磁性金属Ni掺杂更强烈地抑制了LSCO的超导电性可能与材料中晶格的微应变有关. 关键词： 1.85Sr_0.15CuO₄')" href="#">La_1.85Sr_0.15CuO₄ 磁、非磁掺杂 原子结构参量 晶格微应变     

Zn,Ni,Mg高掺杂La1.85Sr0.15CuO4的晶体结构比较

对Zn ,Ni,Mg高掺杂的La1.85Sr0 .15CuO4 (LSCO)超导体的X射线衍射谱进行了仔细的分析 ,从而获得了各掺杂样品的晶格常量、原子结构参量及衍射的峰形参量 ,比较了不同掺杂所引起的晶体结构的差异 ,计算了由于掺杂所产生的晶格内部的微应变 ,结果表明非磁性金属Zn ,Mg掺杂比磁性金属Ni掺杂更强烈地抑制了LSCO的超导电性可能与材料中晶格的微应变有关     

Factors affecting the superconductivity in the process of depositing Nd1.85Ce0.15CuO4-δ by the pulsed electron deposition technique

On SrTiO₃ single crystal substrate, by using the pulsed electron deposition technique, the high-quality electron doped Nd_1.85Ce_0.15CuO_4−δ superconducting film was successfully fabricated. After careful study on the R-T curves of the obtained samples deposited with different substrate temperatures, thicknesses, annealing methods and pulse frequencies, the effects of them on the superconductivity of the films were found, and the reasons were also analyzed. Additionally, by using the same model of the pulsed laser deposition technique, the relation between the target-to-substrate distance and the deposition pressure was drawn out as a quantitative one. Supported by the Key Project of Zhejiang Provincial Natural Science Foundation (Grant No. Z605131), the ‘100 Talents Project’ of Chinese Academy of Sciences, the Creative Research Group of National Natural Science Foundation of China (Grant No. 60321001) and the National Natural Science Foundation of China (Grant No. 60571029)     

La1．85Sr0．15CuO4纳米线阵列的微结构与超导电性

采用溶胶凝胶结合多孔氧化铝硬模板约束的方法，成功制备出直径约30nm的La1．85Sr0．15CuO4纳米线阵列，用XRD与X-ray EDX测定了所制备纳米线的物相与成分；FE-SEM与TEM表征了其形貌特征；由HRTEM与SAKD测量分析了其微结构；磁化强度的测量结果表明样品具有L-30K的超导电性，比块材La1．85Sr0．15CuO4的Tc稍低．分析表明所制各的样品中存在一种α，b轴拉伸，c轴压缩的结构畸变，减弱了铜氧面内Cu3d和O2p轨道的杂化程度，减小了α，b面内的态密度，从而压制了体系的超导电性．     

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.     

Upper limit on the resistivity of La1.85Sr0.15CuO4

The stability of a shielding current in a hollow cylinder of La_1.85Sr_0.15CuO₄ has been studied with a superconducting quantum interference device (SQUID). From the observed lack of decay of the current an upper limit of 3×10^-17ω cm has been established on the resistivity at 4.2 K.     

Spontaneous strain in high-temperature superconductor La1.85Sr0.15CuO4

The lattice parameters of La_1.85Sr_0.15CuO₄ were measured by an x-ray Rietveld method between 15 K and room temperature. A change in a lattice parameter could be detected at superconducting phase transition. It is pointed out, for the first time, that the change can be attributed to a spontaneous strain in the superconducting phase caused by coupling between a superconducting order parameter and the strain.     

柠檬酸盐凝胶法制备La1.85Sr0.15CuO4超导样品工艺研究

采用溶胶凝胶法制备LSCO超导样品.凝胶中不同组元分布均匀,达到分子级的程度,有利于样品成相.通过我们的研究发现,仅在750℃就可以合成具有超导性的LSCO样品;处理过程中通氧,有利于有机物的分解,消除残余碳氮含量.     

Tunneling and point contact investigations of La1.85Sr0.15CuO4

The high-T _c superconductor La_1.85Sr_0.15CuO₄ was investigated by means of point contact and tunneling measurements on small-sized contacts. We find different values for the energy gap at different points of the samples. The ratio 2/k _B T _c ranges from about 3 to 6. For some point contacts we observe a clear signature of a supercurrent. Data for the temperature dependence of the critical current are presented.     

The energy gap of the high Tc superconductor La1.85Sr0.15CuO4

We have measured the energy gap of a polycrystalline sample of La_1.85Sr_0.15CuO₄ using far-infrared reflectance. The sample was prepared by sintering and has a superconducting transition at 36 ±1 K (mid point of a 2K wide region) both in resistance and magnetic susceptibility. The Meissner effect was incomplete and there was considerable absorption below the gap frequency in the superconducting state. The change in far infrared absorption on going to the superconducting state was fitted to the theory of Mattis and Bardeen, yielding an energy gap of (3.2 ± 0.3) kT_c withT_c= 36 K     

Novel in-gap spin state in Zn-doped La1.85Sr0.15CuO4

Low-energy spin excitations of La(1.85)Sr(0.15)Cu(1-y)Zn(y)O4 were studied by neutron scattering. In y=0.004, the incommensurate magnetic peaks show a well-defined "spin gap" below T(c). The magnetic signals at omega=3 meV decrease below T(c)=27 K for y=0.008, also suggesting the gap opening. At lower temperatures, however, the signal increases again, implying a novel in-gap spin state. In y=0.017, the spin gap vanishes and elastic magnetic peaks appear. These results clarify that doped Zn impurities induce the novel in-gap state, which becomes larger and more static with increasing Zn.