高压下新型铁基超导体及稀土六硼化合物的物性研究

发布时间：2018-02-16 16:13

  本文关键词： 高压研究 铁基超导体 稀土六硼化合物 量子临界　出处：《中国科学院大学(中国科学院物理研究所)》2017年博士论文　论文类型：学位论文

【摘要】：本文主要介绍了铁基超导体和稀土六硼化合物的研究概况,并对其中几种典型体系进行了高压研究。采用金刚石压砧(DAC)和Toroid两种不同的高压盒进行了高压下的电阻、霍尔系数、磁化率和热容的测量,并结合同步辐射高压X射线衍射和X射线吸收实验,对研究系统开展了深入、系统的研究。观察到一些有趣的物理现象,讨论了其产生的物理原因,本研究对铁基超导体超导机理及f电子强关联系统的研究具有重要意义。本文主要包括以下四个方面:第一章简要综述了高温超导体的发展历程,对其与传统超导体的区别做了简单介绍。将铜基高温超导体和铁基高温超导体做了一些对比,并重点讲述了铁基超导体中发现的实验规律,最后对高压在超导研究中的应用做了简要介绍。第二章主要介绍了本研究中使用的金刚石对顶压砧(DAC),以及在测量物理量时所使用的方法,同时对实验室的设备进行了简要介绍。第三章主要介绍了对Ca0.73La0.27FeAs2和GdFeAsO0.85的高压研究。在常规的高压电阻、高压磁化率实验之外,通过独特的高压热容测量,在Ca0.73La0.27FeAs2中发现了反铁磁到超导之间的比热突变,并且突变大小随温度上升而增大,最后消失在AFM与SC的边界附近,意味着反铁磁和超导之间双临界点的存在,这一特征在高温超导体中属首次发现。同样通过高压热容测量,在GdFeAsO0.85中发现了“1111”型铁基超导体依然满足BNC标度率(ΔC/TC∝TC2),只是比例系数比“122”型要小,解释了铁基超导体中电子配对机制存在共性。第四章主要介绍了对SmB6和YbB6的高压研究。使用金刚石压砧通过高压电阻、霍尔、X射线衍射和X射线吸收实验,发现SmB6在4GPa时存在异常大的电阻温度依赖系数A,与此同时低温能隙关闭,载流子浓度迅速增加,而压力的增大伴随着Sm离子平均价态的增加和A系数的发散,意味着此时系统发生量子临界相变。在YbB6中发现压力下能隙关闭-再打开的现象,能隙的再打开还伴随着Yb离子平均价态的升高,并且在压力诱导的绝缘态中还发现了类似于SmB6中的低温端电阻平台的存在,对其产生的物理原因做了讨论。
[Abstract]:In this paper, the research situation of iron based superconductors and rare earth hexaboron compounds are introduced, and some typical systems are studied at high pressure. The resistance and Hall coefficient of two kinds of high voltage boxes, including diamond anvil) and Toroid, are carried out at high pressure. The measurement of magnetic susceptibility and heat capacity, combined with the experiments of synchrotron radiation high pressure X-ray diffraction and X-ray absorption, has carried out a deep and systematic study of the research system. Some interesting physical phenomena have been observed and the physical reasons for their formation have been discussed. This study is of great significance to the study of superconducting mechanism and f electron strong correlation system of iron based superconductors. This paper mainly includes the following four aspects: in chapter 1, the development of high temperature superconductors is briefly reviewed. The difference between the superconductor and the traditional superconductor is briefly introduced. Some comparisons between copper based high temperature superconductors and iron base high temperature superconductors are made, and the experimental rules found in iron based superconductors are emphatically described. Finally, the application of high voltage in superconducting research is briefly introduced. Chapter two mainly introduces the diamond anvil DACU used in this study and the methods used in measuring physical quantities. At the same time, the laboratory equipment is briefly introduced. Chapter three mainly introduces the high voltage research of Ca0.73La0.27FeAs2 and GdFeAsO0.85. In addition to the conventional high voltage resistance and high voltage magnetic susceptibility experiment, the special high voltage heat capacity measurement is adopted. The specific heat mutation between antiferromagnetism and superconducting has been found in Ca0.73La0.27FeAs2, and the magnitude of the mutation increases with the increase of temperature, and finally disappears near the boundary between AFM and SC, which means the existence of a double critical point between antiferromagnetism and superconductivity. This feature is first found in high temperature superconductors. By measuring high pressure heat capacity, it is also found in GdFeAsO0.85 that the "1111" iron based superconductors still satisfy the BNC scale rate (螖 C / TC 鈭，

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