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The flux motion and the symmetry of the Cooper pairs in a high-Tc superconductors

高温超导体中的磁通运动和库珀对的对称性

基本信息

批准号：
09450003
负责人：
NOJI Takashi
金额：
$ 7.74万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

项目摘要

Single crystals of the representative high-Tc superconductor YBaィイD22ィエD2CuィイD23ィエD2OィイD27ィエD2 are usually twinned. The twin boundaries prevent us from studying the intrinsic physical properties of the material. On the other hand, it is known that (Ca,La,Ba)ィイD23ィエD2CuィイD23ィエD2OィイD2yィエD2(CLBCO) and NdBaSrCuィイD23ィエD2OィイD2yィエD2(NBSCO) among the 1-2-3 type superconductors are tetragonal in the crystal structure. Therefore, superconducting single-crystals of these compounds must be twin-free. We tried the single-crystal growth of CLBCO and NBSCO by the travelling-solvent floating zone method to obtain originally twin-free single-crystals of the 1-2-3 type superconductors. Trying various kinds of solvent, we have succeeded in obtaining single crystals with the dimensions of the order of 1×1×0.5mmィイD113ィエD1. As-grown single-crystals of CLBCO and NBSCO are tetragonal and non-superconducting. Through the annealing in oxygen, single crystals of CLBCO have became superconductors with Tc=55 - 65 … More K, keeping the tetragonal structure. On the other hand, single crystals of NBSCO have changed from tetragonal to orthorhombic through the annealing in oxygen, though they have become superconductor with Tc = 55 K.Spin gap of SrィイD214ィエD2CuィイD224ィエD2OィイD241ィエD2 studied by the thermal conductivity.The layered cuprate SrィイD214ィエD2CuィイD224ィエD2OィイD241ィエD2 consisting of two-dimensional CuィイD22ィエD2OィイD23ィエD2 ladder planes (regarded as a spin-1/2 ladder system with two legs) and one-dimensional CuOィイD22ィエD2 chains. The carrier-doped spin ladder systems SrィイD214-xィエD2AィイD2xィエD2CuィイD224ィエD2OィイD241ィエD2 (A=Ca,La) have attracted great interest, triggered by the theoretical prediction on the spin gap and superconductivity. We have investigated the spin gap and the hole pairing in the ladder from the thermal conductivity measurement and found two kinds of spin excitation as predicted theoretically. The observed thermal conductivity κ has been analyzed to be composed of κィイD2phィエD2, κィイD2spinィエD2 and κィイD2holeィエD2 due to phonons, spins and holes, respectively. The spin gap in the ladder estimated from κィイD2spinィエD2 is 〜400K and independent of x(Ca). This is regarded as corresponding to the excitation from spin-singlet to spin-triplet, as those estimate from the neutron scattering. The spin gap estimated from κィイD2holeィエD2 decreases with increasing x(Ca). This is regarded as corresponding to the dissociation of spin-singlet pairs, namely, the dissociation of hole pairs, as those estimate from the NMR measurements. Less

具有代表性的高温超导体YBa γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ。孪晶界使我们无法研究材料的内在物理性质。另一方面,众所周知,(Ca,洛杉矶,Ba)ィイc15ィエD2Cuィイc15ィエD2OィイD2yィエD2 (CLBCO)和NdBaSrCuィイc15ィエD2OィイD2yィエD2 (NBSCO)在1-2-3型超导体中正方的晶体结构。因此，这些化合物的超导单晶必须是无双晶的。我们尝试用行溶剂浮区法生长CLBCO和NBSCO的单晶，得到了1-2-3型超导体的原无双单晶。我们尝试了各种溶剂，成功地获得了尺寸为1×1×0.5mm的单晶。CLBCO和NBSCO的生长单晶是四方的、非超导的。在氧中退火后，CLBCO单晶成为超导体，Tc=55 ~ 65…More K，保持了四边形结构。另一方面，NBSCO单晶经氧退火后由四方晶变为正交晶，但在Tc = 55 K时已成为超导体。用热导率法研究了Sr的自旋间隙，研究了Sr的自旋间隙。分层铜酸盐SrィイD214ィエD2CuィイD224ィエD2OィイD241ィエD2组成的二维铜ィイD22摊位ィエD2Oィイc15ィエD2梯子飞机(视为spin-1/2梯系统用两条腿)和一维措ィイD22摊位ィエD2链。自旋阶梯体系Sr φ φ D214-x φ φ D2A φ φ D2x φ φ D2Cu φ φ D224 φ D2O φ D241 φ D2 （A=Ca,La）由于对自旋隙和超导性的理论预测而引起了人们的极大兴趣。我们从热导率的测量中研究了阶梯中的自旋间隙和空穴配对，发现了两种理论预测的自旋激发。经分析，观察到的导热系数κ分别由声子、自旋和空穴引起的κ D2ph D2、κ D2spin D2和κ D2hole D2组成。由κ D2估计的阶梯自旋间隙为~ 400K，与x（Ca）无关。这与中子散射估计的自旋单重态到自旋三重态的激发相对应。自旋间隙随着x（Ca）的增加而减小。这被认为是对应于自旋单线态对的离解，即从核磁共振测量中估计的空穴对的离解。少