Lattice Instability in High-Temperature Superconductors

在掺杂能级和高温超导电性所在的温度范围附近，材料经常会遇到晶格不稳定性。声学研究表明，La_xCuO_4(LSCO)中的晶格不稳定性和超导转变是相互竞争的。本研究的目的是反转LSCO的晶格不稳定性与超导电性之间的关系，以及参考物质Sr_2RuO_4(SRO)。在Saclay与法国团队的合作下，我们(日本团队)在我们的LSCO和SRO单晶样品上进行了中子实验。对于SRO，我们还与剑桥的一个英国团队合作进行了DeHaas van Alphen(DHvA)实验，以绘制SRO的费米面。我们的工作总结如下：1.我们生长了高质量的LSCO、掺Nd LSCO和SRO单晶，部分晶体用于X射线衍射、超声实验、比热测量…更多的是S、膨胀法和输运系数的测量。另一部分晶体被送到Saclay进行中子实验，一些SRO晶体在剑桥用于dHvA实验。2.我们得到的证据表明，LNSCO中的条纹结构与Tranquada等人报道的相似。但我们应该足够谨慎地等待我们的确定结论，直到我们知道晶格缺陷对结构的影响。我们成功地详细分析了SRO的晶格结构，其结果已经发表在Physica C.3上。我们可以从dHvA实验中确定SRO的费米面，这使得我们能够定量地讨论SRO的输运性质以及电子比热。结果和讨论发表在我们最近的四篇论文中。4.我们还在非金属平面外导电、由于LNBCO的1/8反常引起的费米能级附近的态密度分裂以及SRO中可能的p波配对方面获得了各种新的发现。较少

In the vicinity of the doping level and the temperature range where the high-temperature superconductivity appcars, materials often encounter the lattice instability. From our acoustic study, the lattice instability and supercondueting transition are suggested to compete with each other in La_<2-x>Sr_xCuO_4 (LSCO). The aim of this research project is to inverstigatethe relation between the lattice instability and the superconductivity in LSCO and the reference material Sr_2RuO_4 (SRO). In collaboratin with a French group at Saclay, we (Japanese group) performed neutron experiments on our single-crystalline samples of LSCO and SRO.For SRO,we collaborated also with a British group at Cambridge on the deHaas van Alphen (dHvA) experiments to map the Fermi surface of SRO.Our works can be summarized as follows.1.We grew high-quality single crystals of LSCO,Nd-doped LSCO (LNSOC) and SRO.Part of the crystals were used for the X-ray diffraction, ultrasonic experiments, specific heat measurement … More s, dilatometry and measurements of transport coefficients. Another part of the crystals were sent to Saclay for the neutron experiments and some SRO crystals were used at Cambridge for the dHvA experiments.2.We obtained an evidence suggesting the stripe structure in LNSCO similar to what has been reported by Tranquada et al.But we should be careful enough to wait for our definite conclusion until we know the influence of lattice imperfection on the structure. We succeeded in analyzing the lattice structure of SRO in detail, the result of which has been published in Physica C.3.We could determine the Fermi surface for SRO from the dHvA experiment, which allowed us to discuss quantitatively the transport properties as well as the electronic speific heat. The result and discussion are published in four pieces of our recent papers.4.We also obtained various new findings on the nonmetallic out-of-plane conduction, the splitting of the density of states near the Fermi level due to the 1/8 anomaly in LNBCO as well as on the possible p-wave pairing in SRO. Less