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NMR STUDY OF HEAVY FERMION SUPERCONDUCTOR AT ULTRA LOW TEMPERATURE.

超低温重费米子超导体的核磁共振研究。

基本信息

批准号：
62460030
负责人：
PROFESSER ASAYAMA Kunisuke
金额：
$ 4.93万
依托单位：
OSAKA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1988
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-62460030/
关键词：
Ultra low temperature NMR Heavy fermion superconductor Anisotropic superconductor 反強磁性超伝導

项目摘要

WE DEVELOPED AN ULTRA LOW TEMPERATURE NMR TECHNIQUE BY RECONSTRUCTING THE HEAT EXCHANGER AND BY CONSTRUCTING A NEW TYPE MIXING CHAMBER FOR NMR IN ^3He-^4He DILUTION REFRIGERATOR. FOLLOWING RESULTS HAVE BEEN OBTAINED BY USING THIS APPARATUS.1. CeCu_2Si_2 THE KNIGHT SHIFT K OF Si AND Cu ARE COMFIRMED TO DECREASE TO -50% OF THE NORMAL VALUE BELOW T_c DOWN TO 60mK. TOGETHER WITH THE T^3 DEPENDENCE OF T_1^<-1> ALREADY OBSERVED, THE RESULT SHOWS A d WAVE COOPER PAIRING IS REALIZED IN THE SUPERCONDUCTING STATE.IN THE EXTERNAL FIELD OF -3T, WHERE THE SUPERCONDUCTIVITY IS DESTROYED, THE NMR SIGNAL IS FOUND TO DECREASE WITH LOWERING TEMPERATURE, INDICATING AN ANTIFERROMAGNETIC LIKE ORDERING TO APPEAR BELOW -0.6K.2. UPt_3 K OF Pt BELOW T_c DOES NOT CHANGE BELOW T_c DOWN TO 50 mK, WHILE T_1^<-1> OF Pt DOES NOT SHOW BCS TYPE ENHANCEMENT JUST BELOW T_c DECREASING IN PROPORTION TO T^3 AT LOW TEMPERATURE. THIS INDICATES THAT THE SUPERCONDUCTING NATURE IS EITHER SINGLET d WAVE STRONG SPIN-ORBIT SCATTERING OR TRIPLET p WAVE. PERFECT NO-CHANGE OF K SEEMS TO SUPPORT THE LATTER. NO INDICATION OF MAGNETIC ORDERING IS OBSERVED WHICH IS REPORTED BY SR AND NEUTRON DIFFRACTION MEASUREMENT.THE ANISOTROPIC NATURE OF THE SUPERCONDUCTIVITY OBSERVED IN CeCu_2Si_2 AND UPt_3 INDICATES THE EXISTENCE OF A STRONG ON-SITE CONLOMB REPULSION. THE ANTIFERROMAGNETIC SPIN FLUCTUATIONS ARE CONSIDERED TO BE THE ORIGIN OF THE OCCURRENCE FOR THE SUPERCONDUCTIVITY.3. CeAl_3 AND CeInCu_2 WE HAVE FOUND AN ANTIFERROMAGNETIC LIKE ORDERING IN CeAl_3 AND CeInCu_2 AT 1.2 AND 1.1K, RESPECTIVELY, FROM THE T_2 AND LINE WIDTH MEASUREMENT OF A1, Cu and In.

本文通过改造热交换器和在^3He-^4He稀释制冷机中建造新型核磁共振混合室，实现了超低温核磁共振技术。通过使用本战斗机获得了以下结果。1. CeCu_2Si_2合金中Si和Cu的K值在T_c以下下降到正常值的-50%，低于60 mK。结合已观察到的T_1 ~ 3依赖<-1>性，结果表明在超导态下实现了d波库珀对，在超导性被破坏的-3T外场中，核磁共振信号随温度降低而减弱，表明在-0.6K以下出现了类反铁磁有序。在低温下，Pt的T_1 ^在低于T_c时不表现出<-1>BCS型的增强，而在低于T_c时，Pt的T_1^与T_3成比例地减小。这表明超导本质是单重d波强自旋轨道散射或三重p波。K的完全不变似乎支持后者。SR和中子衍射测量报告没有观察到磁有序的迹象。在CeCu_2Si_2和UPt_3中观察到的超导电性的各向异性性质表明存在强烈的现场ConloMB排斥。反铁磁自旋涨落被认为是超导电性的起源. CeAl_3和CeInCu_2的T_2和线宽测量结果表明，在1.2K和1.1K下，CeAl_3和CeInCu_2中存在反铁磁有序。