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Spin-charge ordering and charge dynamics in electron-doped high-Tc superconductors

电子掺杂高温超导体中的自旋电荷排序和电荷动力学

基本信息

批准号：
10440100
负责人：
TAKURA Yoshinori
金额：
$ 7.74万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

We have grown single crystals of Nd_<2-x>Ce_xCuO_<4+y> (x=0, 0.05, 0.1, 0.125, 0.15) by traveling solvent floating zone method and have investigated the temperature dependence of charge and lattice dynamics by the measurements of optical reflectivity spectra. In the as-grown crystals with x=0.05, 0.10, 0.125, we have observed pseudo-gap structure and anomalies in phonon modes at low temperatures which are similar to those observed in non-superconducting sample with x=0.15. This indicates the presence of instability to-ward charge-ordering or electronic phase separation for a broad range of doping levels in this system. The difference from the sample with x=0.15 consists of two points, namely, the increased energy of the pseudo-gap structure and the increased onset temperature of the pseudo-gap with reduced doping-levels.We have also investigated the reduced crystal with x=0.125 that is in the vicinity of superconducting-nonsuperconducting trasition point. The resistivity shows metallic be-havior, but at low temperature it shows a modest uptern and does not exhibit the super-conductivity. The pseudo-gap structure has been observed to open up at a slightly higher temperature than the resistivity uptern also in this sample. This strongly suggests that the instability that is responsible for the pseudo-gap suppresses the superconductivity in this electron-doped system.

我们用流动溶剂浮区法生长出了Nd_<2-x>Ce_xCuO_<4+y> (x= 0,0.05, 0.1, 0.125, 0.15)的单晶，并通过光学反射光谱的测量研究了电荷和晶格动力学的温度依赖性。在x=0.05, 0.10, 0.125的生长晶体中，我们观察到低温下声子模式的赝隙结构和异常，与x=0.15的非超导样品相似。这表明在该系统中，在广泛的掺杂水平范围内，存在向电荷有序或电子相分离的不稳定性。与x=0.15样品的差异包括两个点，即随着掺杂水平的降低，赝隙结构的能量增加和赝隙的起始温度升高。我们还研究了在超导-非超导过渡点附近x=0.125的还原晶体。电阻率表现为金属行为，但在低温下表现为适度上升，不表现出超导性。在该样品中，也观察到赝隙结构在略高于电阻率上升的温度下打开。这有力地表明，伪间隙的不稳定性抑制了电子掺杂体系的超导性。