Dielectric constant of insulating copper oxides including parent insulators of high-temperature superconductors

包括高温超导体母体绝缘体在内的绝缘氧化铜的介电常数

基本信息

批准号：
13640374
负责人：
TERASAKI Ichiro
金额：
$ 2.3万
依托单位：
Waseda University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2004
项目状态：
已结题

项目摘要

The aim of the present project is to prepare single crystals of insulating copper oxides including parent insulators of high-temperature superconductors, to measure anisotropic dielectric constants as functions of temperature and frequency, and to clarify unique features to dielectric response in the parent insulators.Through this project, we have successful synthesized Bi_2Sr_<2-x>La_xCaCu_2O_8 as the least disordered parent insulator of the Bi-2212-type super conductor. We have also synthesized the Pb-substituted insulators (Bi,Pb)_2Sr_2ErCu_2O_8 with no superstructure in the BiO layer, which has been used for photoemission and scanning-tunneling-microscope(STM) experiments. These samples clealy exhibit the dielectric relaxation described by extended Debye-type relaxation, which suggest that the carrier density is spatially inhomogeneous in the CuO_2 plane. In fact, the STM experiment has shown that the pseudo-gap is inhomogenous in space.Among the insulating copper oxides, CaCu_3T_<14>O_<12> shows unusual substitution effects, where only 2% Mn can suppress the gigantic dielectric constant. This could be a clue to the elucidation of the dielectric response. We have further investigated the dielectric response of the conducting organic salts theta-(BEDT-TTF)_2MM'(SCN)_4(M=Rb and Cs, M'=Co and Zn), where charge order domains are inhomogeneously distributed. Most unexpectedly we have found gigantic nonlinear conduction for M=Cs, which would break a new ground to the condensed-matter physics.

本项目的目的是制备绝缘铜氧化物单晶，包括高温超导体的母体绝缘体，测量各向异性介电常数随温度和频率的变化，并阐明母体绝缘体介电响应的独特特征。在本项目中，我们成功合成了Bi_2Sr_<2-x>La_xCaCu_2O_8作为Bi-2212型超导体的无序度最小的母绝缘体。我们还合成了BiO层中无超结构的Pb取代绝缘体(Bi,Pb)_2Sr_2ErCu_2O_8,并用于光电发射和扫描隧道显微镜(STM)实验。这些样品清楚地表现出扩展德拜型弛豫所描述的介电弛豫，这表明载流子密度在 CuO_2 平面上空间不均匀。事实上，STM实验已经表明赝能隙在空间上是不均匀的。在绝缘铜氧化物中，CaCu_3T_<14>O_<12>表现出不寻常的替代效应，仅2%的Mn就可以抑制巨大的介电常数。这可能是阐明介电响应的线索。我们进一步研究了导电有机盐 theta-(BEDT-TTF)_2MM'(SCN)_4(M=Rb 和 Cs, M'=Co 和 Zn) 的介电响应，其中电荷有序域分布不均匀。最出乎意料的是，我们发现了 M=Cs 的巨大非线性传导，这将为凝聚态物理开辟了新天地。