权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Borocarbide Superconductors, Materials and Properties

硼碳化物超导体、材料和性能

基本信息

批准号：
07454077
负责人：
TAKAGI Hidenori
金额：
$ 4.93万
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：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

Physical properties of borocarbide superconductors, LuNi_2B_2C and YNi_2B_2C,have been investigated by using a variety of experimental probes. These compounds were found to be clean limit type II superconductors with the upper and lower critical fields, -10T and -0.1T,respectively. Despite the layred structure, any significant anisotropy in the critical fields with fields parallel and perpendicular to the NiB plane was not observed, indicating that the borocarbides are electronically three dimensional rather than two dimensional. A relatively large electronic specific coefficient gamma=18mJ/molK^2 was estimated from the temperature dependent specific heat of LuNi_2B_2C,implying that the high density of states, associated with the presence of a narrow Ni3d band at the Fermi level, is part of the reason for the high-Tc.The high density of state, on the other hand, suggests the importance of electron correlation effects. Indeed, we have shown experimentally that the strong electron correl … More ation indeed plays a very important role in the borocarbides. The resistivities of LuNi_2B_2C and YNi_2B_2C single crystals were found to show T^2-dependence at low temperatures, with the coefficient A satisfying Kadowaki-woods relationship which holds for a variey of correlated Fermi liquids. We found that the Ni 3d bandwidth of YNi_2B_2C determined by photoemission (with Fujimori group) is 20% narrower than the one estimated from the band calculation, which can be ascribed to the correlation efect. The ^<11>B and ^<61>Ni NMR measurements on LuNi_2B_2C and YNi_2B_2C (with Yasuoka group) indicated a strong enhancement of (T_1T)^<-1> in contrast to the weakly temperature dependent Knight shift. The borocarbide is therefore a superconductors with strong antiferromagnetic spin fluctuations.Symmetry of Cooper pairs have been investigated through the quasiparticle states within the vortex core. Magnetic field dependence of the specific heat of LuNi_2B_2C was measured by a relaxation calorimeter. We found that the electronic specific heat coefficient gamma depends on the magnetic field H as gamma *ROO<H>, in contrast to those expected for conventional superconductors with an isotropic gap, gamma*H.This anomalous field dependence of gamma can be understood by assuming the presence of a gapless region on the Fermi surface. Considering the presence of significant spin fluctuations in the compound, we therefore suggest-d-wave superconductivity in this compound. Less

用各种实验探针研究了硼碳化物超导体LuNi_2B_2C和YNi_2B_2C的物理性质。这些化合物都是洁净极限II型超导体，其上、下临界场分别为-10T和-0.1T。尽管层状结构，任何显着的各向异性在临界领域与场平行和垂直于NiB平面没有观察到，表明硼碳化物是电子三维，而不是二维的。由LuNi_2B_2C的比热随温度的变化估算出较大的电子比热系数γ = 18 mJ/molK^2，这意味着与费米能级处的窄Ni 3d带有关的高态密度是导致高Tc的部分原因，而高态密度则表明电子相关效应的重要性.事实上，我们已经通过实验证明，强电子与 ...更多信息在硼碳化物中，氧化确实起着非常重要的作用。在低温下，LuNi_2B_2C和YNi_2B_2C单晶的折射率与T^2有关，其系数A满足Kadowaki-Woods关系，该关系适用于各种相关费米液体。我们发现，用光电发射谱（带藤森群）测定的YNi_2B_2C的Ni 3d带宽比用能带计算的带宽窄20%，这可归因于相关效应。对<11><61>LuNi_2B_2C和YNi_2B_2C（Yasuoka群）的~（1B）和~（1B）Ni NMR测量表明，（T_1T）~* 的增强<-1>与温度依赖性较弱的Knight位移相反。因此，硼碳化物是一种具有强反铁磁自旋涨落的超导体。通过涡核内的准粒子态研究了库珀对的对称性。用弛豫量热计测量了LuNi_2B_2C的比热随磁场的变化。我们发现，电子比热系数γ取决于磁场H为γ *ROO<H>，在与传统的超导体与各向同性的间隙，γ *H的预期相反。这种异常的场依赖性的γ可以通过假设费米表面上的无间隙区域的存在下理解。考虑到该化合物中存在显著的自旋涨落，因此我们在该化合物中发现了最大d波超导性。少