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^<13>C NMR in borocarbide superconductor

硼碳化物超导体中的^ 13 C NMR

基本信息

批准号：
08640464
负责人：
MIZUNO Kiyoshi
金额：
$ 1.22万
依托单位：
The University of Tokushima
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

Quaternary borocarbide intermetallic compounds RM_2B_2C (R = rare-earth element, M=transition metal element) show a relatively high superconducting transition temperature T_c The effect of electron correlation is expected to be important because the d-electron of transition metal plays a leading actor of conduction. From ^<13>C,^<11>B NMR,the detailed information on the electronic properties of borocarbide superconductor YNi_2B_2C is obtained in normal and superconducting state.1. In the normal state, the existence of the antiferromagnetic spin fluctuation was suggested. The spin-lattice relaxation rate T_1^<-1> and Knight shift K of ^<13>C and ^<11>B NMR show that the isotropic (Fermi contact) interaction between 2s conduction electron spin and nuclear spin at the carbon site and the boron site is dominant. The temperature dependences of T_1^<-1> and K is explained well by the Korringa mechanism. These temperature dependences are attributed to that of spin susceptibility, which is the consequence of band structure. No antiferromagnetic spin fluctuation is observed in ^<13>C and ^<11>B NMR.Strength of the electro-electron interaction is the same order as that found in alkali metal. These experimental results agree well with the results of band calculation.2. In the superconducting state, a small coherence (Hebel-Slichter) peak is obsereved, which testified the borocarbide compounds to be a conventional phonon-mediated s wave (BCS) superconductors. From the temperature dependence of <@D113@>D1CT<@D21@>D2<@D1-1@>D1, a superconducting gap parameter of 2DELTA<@D20@>D2/k<@D2B@>D2T<@D2C@>D2 = 3.30(]SY.+-。[)0.08 is obtained. The borocarbide compound being a conventional BCS superconductor is consistent with the normal properties of the Fermi liquid picture in the normal state.

四元硼碳化物金属间化合物RM_2B_2C（R =稀土元素，M=过渡金属元素）具有较高的超导转变温度T_c，过渡金属的d电子起主导导电作用，电子关联效应是重要的。从~ <13>1C，<11>~ B NMR谱中，获得了硼碳超导体YNi_2B_2C在正常态和超导态下的电子性质的详细信息.在正常状态下，反铁磁自旋涨落的存在被提出。~ 1C和~ 1B B NMR的自旋-晶格弛豫速率T_1^<-1>和Knight位移K<13><11>表明，碳位和硼位的2s传导电子自旋与核自旋之间的各向同性（费米接触）相互作用占主导地位。用<-1>Korringa机制很好地解释了T_1^和K的温度依赖性。这些温度依赖性归因于自旋磁化率，这是能带结构的结果。在~ 1C和~ 1H ~+ B NMR谱中没有观察到反铁磁自旋涨落<13><11>，电子-电相互作用强度与碱金属中的电子-电相互作用强度相同。实验结果与能带计算结果吻合较好.在超导态下，观察到一个小的相干峰（Hebel-Slichter），证明该化合物是一种声子介导的s波超导体。由<@D113@>D1CT<@D21@>D2<@D1-1@>D1的温度依赖性，得到超导能隙参数2 Δ D20/k D2 T <@D2C = 3.30（±）SY. [0.08]得到。硼碳化合物是一种传统的BCS超导体，与正常状态下费米液体图像的正常性质一致。