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Heavy Fermion State in the Pr-based Skutterudites

镨基方钴矿中的重费米子态

基本信息

批准号：
13640369
负责人：
AOKI Yuji
金额：
$ 2.62万
依托单位：
Tokyo Metropolitan University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640369/
关键词：
Strongly correlated electron system Heavy fermion state filled skutterudite specific heat heavy fermion superconductivity quadrupole ordering anisotropic superconductivity muSR トンネル微分抵抗測定

项目摘要

1. Pr-based heavy fermion compound PrFe_4P_<12>(1) By neutron scattering, muSR, nuclear specific heat measurements, the anomalous ordered state appearing below 6.5 K is found to be nonmagnetic. Considering the crystalline electric field (CEF) effect, it is highly probable to be an antiferro quadrupole ordered state. Using high quality single crystalline samples, field-temperature phase diagram has been determined. By applying the resonance level model, the energy scale of the heavy fermion state (or Kondo temperature) has been determined.(2) It is found that the substitution of La ions to Pr sites suppress the ordered state and makes the heavy fermion state restored even in zero field, suggesting that the quadruple ordering and the heavy fermion state are competing each other.2. Pr based heavy fermion superconductor PrOs_4Sb_<12>(1) Double jump structure at the superconducting phase transition has been confirmed and the field-vs-temperature phase diagram has been constructed by specific heat measurements. Using muSR technique, we found an internal magnetic field appearing in the superconducting state, which is the undoubted evidence for the broken time-reversal symmetry in the superconductivity; the first known instance of its kind in metallic materials.(2) By specific heat measurements, we discovered a field-induced ordered phase and confirmed that it is an antiferro quadrupole ordered state by neutron scattering. Based on this result, we proposed the most appropriate CEF level scheme.

1. (1)通过中子散射、muSR、核比热测量，发现在6.5 K以下出现的异常有序态是非磁性的。考虑到晶体电场效应，极有可能为反铁四极有序态。利用高质量的单晶样品，确定了场温相图。应用共振能级模型，确定了重费米子态（近藤温度）的能量尺度。(2)发现La离子取代Pr位点抑制了有序态，即使在零场下也能恢复重费米子态，表明四重有序态和重费米子态是相互竞争的。证实了Pr基重费米子超导体PrOs_4Sb_<12>(1)超导相变的双跳变结构，并通过比热测量建立了场温相图。利用muSR技术，我们发现了超导状态下出现的内部磁场，这是超导中时间反转对称性被打破的确凿证据；这是金属材料中已知的第一个实例。(2)通过比热测量，发现了场致有序相，并通过中子散射证实其为反铁四极有序态。在此基础上，我们提出了最合适的基金水平方案。