Lattice Instability in High-Temperature Superconductors

在高温超导出现的掺杂水平和温度范围附近，材料往往会出现晶格不稳定性。声学研究表明，La_ Sr_xCuO_4（LSCO）的晶格不稳定性和超晶格跃迁是相互竞争<2-x>的。本课题的目的是研究LSCO和Sr_2RuO_4（SRO）的晶格不稳定性与超导电性之间的关系。我们与萨克雷一个法国小组合作，在SRO方面，我们还与英国剑桥的一个研究小组合作，利用deHaas货车Alphen（dHvA）实验对SRO的费米面进行了测量。对部分晶体进行了X射线衍射、超声波实验、比热测量 ...更多信息 s、电导率测定法和输运系数的测量。另一部分晶体被送往Saclay进行中子实验，部分SRO晶体被用于剑桥的dHvA实验。2.我们得到了类似于Tranquada等人报道的LNSCO中的条纹结构的证据，但我们应该足够谨慎，直到我们知道晶格不完整性对结构的影响，我们才能得到明确的结论。我们成功地对SRO的晶格结构进行了详细的分析，结果发表在Physica C.3上。我们可以通过dHvA实验确定SRO的费米面，从而定量地讨论输运性质和电子比热。4.在非金属离面导电、LNBCO中1/8反常引起的费米能级附近态密度分裂以及SRO中可能存在的p波配对等方面，我们也得到了一些新的发现。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