本文選題：非常規(guī)超導(dǎo)體 + 電子關(guān)聯(lián)系統(tǒng)　； 參考：《南京大學(xué)》2016年博士論文

【摘要】：非常規(guī)超導(dǎo)體是不能用以聲子作為配對(duì)媒的傳統(tǒng)BCS理論理解的超導(dǎo)體,主要有銅氧化物超導(dǎo)體、鐵基超導(dǎo)體、重費(fèi)米子超導(dǎo)體和有機(jī)超導(dǎo)體等。經(jīng)過(guò)近半個(gè)世紀(jì)的研究,物理學(xué)家們雖然認(rèn)為非常規(guī)超導(dǎo)的誘發(fā)與磁性漲落和量子臨界現(xiàn)象有關(guān),但至今仍無(wú)法對(duì)其找到完備而統(tǒng)一的描述方式。因此,發(fā)現(xiàn)新型非常規(guī)超導(dǎo)體系以提供新的研究平臺(tái),并對(duì)其進(jìn)行物性研究得到更多非常規(guī)超導(dǎo)機(jī)理的線索,就成了非常重要的課題。本篇論文基于尋找非常規(guī)超導(dǎo)材料的基本原則性思路,對(duì)探索基于過(guò)渡金屬化合物的新型超導(dǎo)體做了一些有益嘗試。本篇論文的第一部分首先概括了常規(guī)超導(dǎo)現(xiàn)象及物理圖像,并簡(jiǎn)單介紹了銅氧化物超導(dǎo)體、鐵基超導(dǎo)體、重費(fèi)米子超導(dǎo)體和有機(jī)超導(dǎo)體四類非常規(guī)超導(dǎo)體,然后對(duì)歷史上發(fā)現(xiàn)非常規(guī)超導(dǎo)的各種嘗試做了回顧和梳理,并嘗試提出了探索非常規(guī)超導(dǎo)材料的基本原則性思路,最后介紹了設(shè)計(jì)鈷、鎳基高溫超導(dǎo)的一個(gè)實(shí)例。論文的第二部分介紹了我們所使用的晶體生長(zhǎng)、表征方法,和電輸運(yùn)測(cè)量、熱輸運(yùn)測(cè)量、磁性測(cè)量、高壓測(cè)量的實(shí)驗(yàn)及分析方法。論文第三部分我們以LaRu2P2材料為平臺(tái)對(duì)Ru基122系統(tǒng)中可能存在的電子關(guān)聯(lián)效應(yīng)進(jìn)行研究。我們?cè)贚aRu2P2單晶中觀測(cè)到了超導(dǎo)轉(zhuǎn)變溫度Tc隨壓力P的增強(qiáng),這不能由麥克米蘭理論完全理解。關(guān)于正常態(tài)電阻以及上臨界場(chǎng)的自洽分析暗示某些額外關(guān)聯(lián)性質(zhì)的電子-玻色子相互作用可能在壓力下被誘發(fā),成為超導(dǎo)性質(zhì)增強(qiáng)的來(lái)源。基于電子及聲子結(jié)構(gòu)的第一性原理計(jì)算,我們分析了關(guān)聯(lián)增強(qiáng)可能的原因,并對(duì)Tc-p中相圖的dome狀結(jié)構(gòu)做出了解釋。我們的實(shí)驗(yàn)表明LaRu2P2與自旋漲落為配對(duì)膠的鐵基超導(dǎo)有一些共通之處,這或許會(huì)在將來(lái)激發(fā)Ru基系統(tǒng)中關(guān)聯(lián)效應(yīng)誘發(fā)新型非常規(guī)超導(dǎo)的研究。論文第四部分是為發(fā)現(xiàn)新超導(dǎo)做出的一些嘗試。我們首先研究了EuPdAs多晶樣品,通過(guò)電阻和磁化數(shù)據(jù)我們可以看到樣品常壓下在180 K存在的相變,當(dāng)我們對(duì)樣品施加靜水壓,僅僅0.48 GPa就將180 K相變完全壓制,并且電阻在壓力下單調(diào)降低,然而加壓直至1.90 GPa都并未看到超導(dǎo)在低溫被誘發(fā)。這說(shuō)明180 K相變可能僅僅是一個(gè)價(jià)態(tài)轉(zhuǎn)換相變,而與長(zhǎng)程磁序無(wú)關(guān)。為了實(shí)現(xiàn)一些奇異電子性質(zhì),我們認(rèn)為使用電子摻雜調(diào)節(jié)Pd原子的4d軌道占據(jù)應(yīng)當(dāng)是必要的途徑。接著我們看到了MnP多晶在高溫區(qū)的鐵磁相變與低溫區(qū)的螺旋磁性相變,磁化上螺旋磁性態(tài)出現(xiàn)了回滯,而高溫區(qū)的鐵磁態(tài)并未建立回滯。我們發(fā)現(xiàn)在高場(chǎng)下螺旋磁性相變會(huì)被壓制,使系統(tǒng)在低溫區(qū)為鐵磁態(tài),而靜水壓下300K左右的鐵磁相變將緩慢往低溫移動(dòng)。我們還討論了絕緣態(tài)RuP向金屬態(tài)CrP的系列摻雜實(shí)驗(yàn),并在Cr60%處看到了可能對(duì)形成超導(dǎo)態(tài)有利的疑似量子臨界現(xiàn)象。論文第五部分首先介紹了一些量子自旋液體態(tài)(QSL)的理論背景,之后對(duì)Kagome格子中的非常規(guī)超導(dǎo)材料LaRu3Si2進(jìn)行了化學(xué)摻雜研究。我們對(duì)La位和Ru位進(jìn)行了不同稀土與過(guò)渡金屬的摻雜,得到了從LaRu3Si2至CeRu3S i2勺全相圖,并發(fā)現(xiàn)稀土與堿土金屬的摻雜對(duì)超導(dǎo)只有較微弱的壓制作用。特別是在Ru位用Cr和Ni磁性元素進(jìn)行的摻雜,對(duì)超導(dǎo)的壓制作用遠(yuǎn)遠(yuǎn)比不上同為磁性原子的Fe元素。通過(guò)居里外斯定律擬合分析,我們得到雜質(zhì)元素Cr和Ni局域磁矩非常小,顯示它們的確未像Fe元素那樣建立較強(qiáng)的局域磁性散射中心,而僅僅扮演了類似巡游磁矩的角色。論文第六部分是全文的總結(jié)。
[Abstract]:Unconventional superconductors are superconductors that can not be understood by traditional BCS theory with phonons as pairing medium. They are mainly copper oxide superconductors, iron based superconductors, heavy fermion superconductors and organic superconductors. After nearly half a century of research, physicists believe that the induced and magnetic fluctuations and quantum critical phenomena of unconventional superconductors are considered. So far, it is not possible to find a complete and unified description of it. Therefore, it is very important to find a new unconventional superconductor system to provide a new research platform and to study its physical properties to get more unconventional superconducting mechanisms. This article is based on the basic principles of finding unconventional superconducting materials. The first part of this paper first summarizes the conventional superconductivity and physical images, and briefly introduces the four kinds of unconventional superconductors, such as copper oxide superconductors, Tie Jichao conductors, heavy fermion superconductors and organic superconductors. All attempts to find unconventional superconductivity have been reviewed and combed in history, and the basic principles for exploring unconventional superconducting materials are put forward. Finally, an example of the design of cobalt and nickel based high temperature superconductors is introduced. The second part of the thesis introduces the crystal growth, characterization, electrical transport measurement and thermal transport measurements we have used. In the third part of the paper, we have studied the possible electronic correlation effect in the Ru based 122 system with the LaRu2P2 material as a platform. We observed that the superconducting transition temperature Tc is enhanced with the pressure P in the LaRu2P2 single crystal. This can not be fully understood by Macmillan theory. The self consistent analysis of the normal resistance and the upper critical field suggests that the electron boson interaction of some additional associated properties may be induced under pressure and becomes the source of the enhancement of superconducting properties. Based on the first principle calculation of the electron and phonon structures, we analyzed the reasons for the correlation enhancement and the dome structure of the phase diagram in Tc-p We have made an explanation. Our experiments show that LaRu2P2 has some similarities with the iron base superconductor of the spin fluctuation, which may stimulate the study of the new unconventional superconductivity induced by the association effect in the Ru based system in the future. The fourth part is the attempt to find new superconductivity. We first studied the EuPdAs polycrystal sample, Through the resistance and magnetization data we can see the phase transition at 180 K under the normal pressure. When we apply the static pressure to the sample, only 0.48 GPa will completely suppress the 180 K phase transition, and the resistance is monotonically reduced under pressure. However, the pressure until 1.90 GPa does not see the superconductor being induced at low temperature. This indicates that the 180 K phase transition may be only only possible. In order to realize some singular electron properties, we think that the use of electronic doping to regulate the 4D orbit of Pd atoms should be a necessary way to realize some singular electron properties. Then we see the ferromagnetic phase transition of MnP polycrystals in the high temperature region and the spiral magnetic phase transition in the low temperature region, and the appearance of the spiral magnetic state on the magnetization. We found that the ferromagnetic state of the high temperature region did not establish hysteresis. We found that the magnetic phase transition in the high field will be suppressed and the system is ferromagnetic in the low temperature region, and the ferromagnetic phase transition of about 300K under static water pressure will move slowly to the low temperature. We also discuss the series doping experiments of the insulating state RuP to the metal state CrP, and see it at Cr60%. In the fifth part of this paper, the theoretical background of some quantum spin fluid states (QSL) is introduced, and then the chemical doping of the unconventional superconducting material LaRu3Si2 in the Kagome lattice is studied. The doping of different rare earth and transition metals in the La and Ru sites is obtained. The full phase diagram from LaRu3Si2 to CeRu3S I2 spoon is found, and the doping of rare earth and alkaline earth metal has only a weaker suppression effect on superconductivity. Especially in the Ru bit doping with Cr and Ni magnetic elements, the suppression of superconducting is far less than the Fe element of the magnetic atom. The local magnetic moments of elements Cr and Ni are very small, showing that they do not establish strong local magnetic scattering centers like Fe elements, but only play a role similar to the parade magnetic moment. The sixth part of the paper is the summary of the full text.

【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：O469

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