本文關(guān)鍵詞： 高壓研究 鐵基超導(dǎo)體 稀土六硼化合物 量子臨界　出處：《中國科學(xué)院大學(xué)(中國科學(xué)院物理研究所)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：本文主要介紹了鐵基超導(dǎo)體和稀土六硼化合物的研究概況,并對(duì)其中幾種典型體系進(jìn)行了高壓研究。采用金剛石壓砧(DAC)和Toroid兩種不同的高壓盒進(jìn)行了高壓下的電阻、霍爾系數(shù)、磁化率和熱容的測(cè)量,并結(jié)合同步輻射高壓X射線衍射和X射線吸收實(shí)驗(yàn),對(duì)研究系統(tǒng)開展了深入、系統(tǒng)的研究。觀察到一些有趣的物理現(xiàn)象,討論了其產(chǎn)生的物理原因,本研究對(duì)鐵基超導(dǎo)體超導(dǎo)機(jī)理及f電子強(qiáng)關(guān)聯(lián)系統(tǒng)的研究具有重要意義。本文主要包括以下四個(gè)方面:第一章簡(jiǎn)要綜述了高溫超導(dǎo)體的發(fā)展歷程,對(duì)其與傳統(tǒng)超導(dǎo)體的區(qū)別做了簡(jiǎn)單介紹。將銅基高溫超導(dǎo)體和鐵基高溫超導(dǎo)體做了一些對(duì)比,并重點(diǎn)講述了鐵基超導(dǎo)體中發(fā)現(xiàn)的實(shí)驗(yàn)規(guī)律,最后對(duì)高壓在超導(dǎo)研究中的應(yīng)用做了簡(jiǎn)要介紹。第二章主要介紹了本研究中使用的金剛石對(duì)頂壓砧(DAC),以及在測(cè)量物理量時(shí)所使用的方法,同時(shí)對(duì)實(shí)驗(yàn)室的設(shè)備進(jìn)行了簡(jiǎn)要介紹。第三章主要介紹了對(duì)Ca0.73La0.27FeAs2和GdFeAsO0.85的高壓研究。在常規(guī)的高壓電阻、高壓磁化率實(shí)驗(yàn)之外,通過獨(dú)特的高壓熱容測(cè)量,在Ca0.73La0.27FeAs2中發(fā)現(xiàn)了反鐵磁到超導(dǎo)之間的比熱突變,并且突變大小隨溫度上升而增大,最后消失在AFM與SC的邊界附近,意味著反鐵磁和超導(dǎo)之間雙臨界點(diǎn)的存在,這一特征在高溫超導(dǎo)體中屬首次發(fā)現(xiàn)。同樣通過高壓熱容測(cè)量,在GdFeAsO0.85中發(fā)現(xiàn)了“1111”型鐵基超導(dǎo)體依然滿足BNC標(biāo)度率(ΔC/TC∝TC2),只是比例系數(shù)比“122”型要小,解釋了鐵基超導(dǎo)體中電子配對(duì)機(jī)制存在共性。第四章主要介紹了對(duì)SmB6和YbB6的高壓研究。使用金剛石壓砧通過高壓電阻、霍爾、X射線衍射和X射線吸收實(shí)驗(yàn),發(fā)現(xiàn)SmB6在4GPa時(shí)存在異常大的電阻溫度依賴系數(shù)A,與此同時(shí)低溫能隙關(guān)閉,載流子濃度迅速增加,而壓力的增大伴隨著Sm離子平均價(jià)態(tài)的增加和A系數(shù)的發(fā)散,意味著此時(shí)系統(tǒng)發(fā)生量子臨界相變。在YbB6中發(fā)現(xiàn)壓力下能隙關(guān)閉-再打開的現(xiàn)象,能隙的再打開還伴隨著Yb離子平均價(jià)態(tài)的升高,并且在壓力誘導(dǎo)的絕緣態(tài)中還發(fā)現(xiàn)了類似于SmB6中的低溫端電阻平臺(tái)的存在,對(duì)其產(chǎn)生的物理原因做了討論。
[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，

本文編號(hào)：1515919