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

硼质超导体，LUNI_2B_2C和YNI_2B_2C的物理特性已通过使用多种实验问题进行了研究。发现这些化合物分别是上下临界场，分别为-10T和-0.1T的干净极限II型超导体。尽管存在铺设结构，但未观察到具有平行且垂直于NIB平面的临界场中的任何明显各向异性，表明硼质核比电子在电子上是三维而不是二维。从LUNI_2B_2C的温度依赖性比热的热量中估算了相对较大的电子特异性系数γ= 18MJ/molk^2，这暗示着与FERMI水平狭窄的Ni3d带有关的状态的高密度是对较高的状态效应的高度密度的原因，该效率是对另一个部门的高密度，提出了corre corron的高度。实际上，我们在实验上表明，强的电子相关性……更多的ation确实在硼核体中起着非常重要的作用。发现LUNI_2B_2C和YNI_2B_2C的抗性单晶在低温下显示出T^2依赖性，核心具有令人满意的Kadowaki-Woods关系，可用于各种相关的Fermi液体。我们发现，通过光发射确定的YNI_2B_2C的Ni 3D带宽（fujimori组）比从频带计算中估计的ni 3D带宽要窄20％，这可以分配给相关效应。 LUNI_2B_2C和YNI_2B_2C（与Yasuoka组）上的 ^<11> b和 ^<61> Ni NMR测量值表明（T_1T） ^<-1>的强烈增强与弱温度依赖的骑士相反。因此，硼质是具有强抗磁性自旋波动的超导体。库珀对的对称性已经通过涡流核心内的准颗粒状态进行了研究。 LUNI_2B_2C的比热的磁场依赖性通过弛豫量热计测量。我们发现，电子特异性热corificγ取决于磁场H作为伽马 *Roo <h>，与具有各向同性间隙的常规超导体预期的相反，伽马 *h。这些异常场依赖性可以通过在菲尔米人表面上存在无异常的区域来理解。考虑到化合物中存在明显的自旋波动，我们建议在该化合物中提出D-D波超导性。较少的