本文選題：銅氧化物高溫超導(dǎo)體 + 鐵基超導(dǎo)體��； 參考：《清華大學(xué)》2014年博士論文

【摘要】：非常規(guī)超導(dǎo)材料的相圖中存在一個(gè)重要的現(xiàn)象,即在其超導(dǎo)相附近往往存在著一個(gè)絕緣相。其中最顯著的例子是銅氧化物高溫超導(dǎo)體,其母體通常被認(rèn)為是一個(gè)反鐵磁關(guān)聯(lián)的Mott絕緣體。最近在鐵基超導(dǎo)材料中也發(fā)現(xiàn)了若干新奇的絕緣態(tài)。了解這些絕緣相的電子結(jié)構(gòu),將有可能對(duì)理解非常規(guī)超導(dǎo)電性形成的機(jī)制有所啟示。本文將闡述我們應(yīng)用掃描隧道顯微鏡技術(shù)對(duì)非常規(guī)超導(dǎo)體中的絕緣相進(jìn)行研究所獲得的結(jié)果。我們?cè)谠映叨葴y(cè)量銅氧化物高溫超導(dǎo)體的母體,Mott絕緣材料Ca2CuO2Cl2的電子結(jié)構(gòu),并首次獲得了跨過(guò)整個(gè)Mott-Hubbard能隙的完整的電子譜。它呈現(xiàn)出電子-空穴對(duì)稱,實(shí)空間均勻分布的特性。由雜質(zhì)引入的載流子在Mott-Hubbard能隙中引發(fā)一個(gè)新的能態(tài),此能態(tài)有很大的能量展寬,并在實(shí)空間高度局域化。我們的實(shí)驗(yàn)數(shù)據(jù)與Zhang-Rice單態(tài)模型大致吻合,但是對(duì)雜質(zhì)所引起電子態(tài)的一些具體特征還需要進(jìn)一步的理論解釋。對(duì)于鐵基超導(dǎo)體,我們測(cè)量了Cu摻雜的NaFeAs體系在超導(dǎo)體-絕緣體相變前后其局域電子結(jié)構(gòu)的演化。我們發(fā)現(xiàn)Cu原子摻雜將系統(tǒng)地降低低能電子態(tài)的譜權(quán)重,并引入很強(qiáng)的局域雜質(zhì)勢(shì)。在絕緣相的電子譜中我們探測(cè)到一個(gè)低能能隙,它使得費(fèi)米面附近的電子態(tài)密度進(jìn)一步降低。尤其值得注意的是絕緣相電子譜的總體線型,以及其空間分布的不均勻性,都與極度欠摻雜的銅氧化物高溫超導(dǎo)體十分類似。我們認(rèn)為Cu原子摻雜對(duì)系統(tǒng)巡游電子態(tài)密度的壓制以及它所引入的雜質(zhì)勢(shì)共同作用,從而在通常呈現(xiàn)金屬性的鐵基系統(tǒng)中導(dǎo)致了一個(gè)強(qiáng)耦合的絕緣態(tài)。
[Abstract]:There is an important phenomenon in the phase diagram of unconventional superconducting materials, that is, there is always an insulating phase near the superconducting phase. The most notable example is the copper oxide high temperature superconductor, the parent of which is generally considered to be an antiferromagnetic associated Mott insulator. A number of novel insulating states have also been recently found in iron-based superconductors. Understanding the electronic structure of these insulating phases may be helpful in understanding the mechanism of formation of unconventional superconductivity. This paper describes the results obtained by using scanning tunneling microscope (SEM) to study the insulating phase in unconventional superconductors. We have measured the electronic structure of Ca2CuO2Cl2, the parent material of copper oxide high temperature superconductors, at atomic scale. For the first time, we have obtained the complete electronic spectra across the entire Mott-Hubbard gap. It presents the characteristics of electron-hole symmetry and uniform distribution in real space. The carrier introduced by impurity induces a new energy state in the Mott-Hubbard gap, which has a large energy broadening and is highly localized in real space. Our experimental data are in good agreement with the Zhang-Rice single state model, but some specific characteristics of the electronic states caused by impurities need further theoretical explanation. For Fe-based superconductors, the evolution of local electronic structures of Cu-doped NaFeAs system before and after superconductor-insulator phase transition has been measured. We find that the doping of Cu atoms will systematically reduce the spectral weight of low energy electronic states and introduce a strong local impurity potential. We have detected a low energy gap in the electron spectrum of the insulating phase, which further reduces the density of electronic states near the Fermi surface. It is particularly noteworthy that the general line of the insulating phase electron spectrum and the heterogeneity of its spatial distribution are very similar to those of highly underdoped copper oxide high temperature superconductors. We consider that Cu doping compacts the density of states in the system and the impurity potential it introduces, which leads to a strongly coupled insulating state in the iron-based system, which usually presents gold properties.
【學(xué)位授予單位】：清華大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TM26

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