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Superconductivity and Nuclear Magnetism due to the Virtual Excitation of the Singlet Ground State

单重态基态虚激发的超导性和核磁性

基本信息

批准号：
07640489
负责人：
ISHII Hiroumi
金额：
$ 0.51万
依托单位：
Osaka City University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
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

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07640489/
关键词：
Singlet Ground State Van Vleck Paramagnetism Crystalline Field State Anisotropic Superconductor Heavy Fermion Nuclear Magnetism Manetic Superconductor Nuclear Spin Relaxation 1重項基底状態ヴァンヴレック常磁性

项目摘要

This project aimed to extend the theory of superconductivity and nuclear magnetism which we had proposed for praseodimium metal and its intermetallic compounds. In our theory an atractive interaction comes from the virtual excitation of the crystal field singlet ground state. We first proved that the Migdal theorem holds for this process and set up the Eliashberg equation. By linearizing it, we obtained the superconducting transition temperature Tc for the cases where the maximum of the conduction electron susceptibility occurs at Q=0 and at the Brillouin zone boundary. For the former, we found p-wave pairing, whose degeneracy of the spin triplet states is lifted at Tc due to the crystalline field anisotropy. For the latter, d-wave pairing occurs. The mechanism to induce the attractive force also induces the mass-enhancement for the conduction electrons, which works to reduce Tc strongly. Although the increase of the s-f exchange interaction and/or the Van Vleck susceptibility augments Tc, it also induces spontaneous magnetization beyond a critical value. In this case, due to the mass enhancement effect, the superconductivity appears only below the magnetic order. This suggests a similarity with UPt3, which is known as a crystal field singlet state system. The phase diagram is obtained. We are also extending the study to derive the s-f exchange interaction from the Anderson Hamiltonian for (4f) <@D12@>D1 with strong Hund and LS couplings. On the basis of it the RKKY interaction is derived for nuclear spins. Relating to these studies we also study the nuclear spin relaxation in ultralow temperatures. In approaching the nuclear ordering, the relaxation deviates from the Korringa law and turns slow. Another study is concerning nuclear spins in the electric quadrupole field, where lz=(]SY.+-。[)I states are the lowest states. The magnetic relaxation behaves as an activation process and turns very slow inultralow temperatures.

本计画的目的是将我们提出的超导与核磁理论延伸至镨金属及其金属间化合物。在我们的理论中，吸引相互作用来自于晶体场单重基态的虚激发。我们首先证明了Migdal定理对这个过程成立，并建立了Eliashberg方程。通过线性化，我们得到了超导转变温度Tc的情况下，最大的传导电子磁化率发生在Q=0和布里渊区边界。对于前者，我们发现了p波配对，其自旋三重态的简并度由于晶场各向异性而在Tc处被提升。对于后者，d波配对发生。诱导吸引力的机制也诱导了传导电子的质量增强，其作用是强烈地降低Tc。虽然s-f交换作用和/或货车Vleck磁化率的增加增大了Tc，但它也诱导自发磁化超过临界值。在这种情况下，由于质量增强效应，超导性只出现在磁序以下。这表明与UPt 3相似，UPt 3被称为晶体场单重态系统。得到了相图。我们还将研究扩展到从具有强Hund和LS耦合的（4f）<@D12@>D1的安德森哈密顿量导出s-f交换相互作用。在此基础上推导出核自旋的RKKY相互作用。与此相关，我们还研究了超低温下的核自旋弛豫。在接近核有序时，弛豫偏离了Korringa定律，变得缓慢。另一项研究是关于电四极场中的核自旋，其中lz=（]SY.+-。[)I国家是最低的国家。磁弛豫表现为激活过程，在超低温下变得非常缓慢。