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PathIntegral Theory for Photoemission Specta of ElectronPhonon Coupled Systems
https://ir.soken.ac.jp/records/664
https://ir.soken.ac.jp/records/6646436f7218f164047968ad31dd66b5bfb
名前 / ファイル  ライセンス  アクション 

要旨・審査要旨 / Abstract, Screening Result (284.6 kB)

Item type  学位論文 / Thesis or Dissertation(1)  

公開日  20100222  
タイトル  
タイトル  PathIntegral Theory for Photoemission Specta of ElectronPhonon Coupled Systems  
タイトル  
タイトル  PathIntegral Theory for Photoemission Specta of ElectronPhonon Coupled Systems  
言語  en  
言語  
言語  eng  
資源タイプ  
資源タイプ識別子  http://purl.org/coar/resource_type/c_46ec  
資源タイプ  thesis  
著者名 
吉, 凱
× 吉, 凱 

フリガナ 
ジ, カイ
× ジ, カイ 

著者 
JI, Kai
× JI, Kai 

学位授与機関  
学位授与機関名  総合研究大学院大学  
学位名  
学位名  博士（理学）  
学位記番号  
内容記述タイプ  Other  
内容記述  総研大甲第744号  
研究科  
値  数物科学研究科  
専攻  
値  13 物質構造科学専攻  
学位授与年月日  
学位授与年月日  20040324  
学位授与年度  
値  2003  
要旨  
内容記述タイプ  Other  
内容記述  It has been a longstanding question in solid state physics, how the electronphonon (eph) interaction influences the electronic energy band structures, and finally determines a material to become an insulator, metal or superconductor. Since the photoemission spectrum can directly probe this structure of electronic energy bands and topology of Fermi surface, it has become one of the most important measurements for the experimental studies. In the angle resolved photoemission spectra (ARPES) , the binding energy can now be measured as a function of each given momentum. With the rapid progress of this high resolution ARPES, the electronic energy band structure can now be discerned in the scale of a few meV. Based on this technical development, quite a lot of new properties associated with eph interaction have been discovered in the normal metallic states as well as in the superconducting (SC) ones, signifying direct and clear evidences for the importance of the eph interactions. On the other hand, theoretical studies for this eph coupling already have a long history. In the case of a single electron coupled with phonons, it has been investigated in detail, by the ordinary perturbation theory, and also by the unitary transformation methods. As for the manyelectron system coupled with phonons, the socalled MigdalEliashberg (ME) theory, and also adiabatic or mean field approximation are often used to clarify the energy band structures, in connection with various phase transition phenomena, such as the charge density wave (CDW) states and superconductor ones from metallic states. In some cases, systematic theoretical methods have already been devised to take into account high order corrections, which are not included in the ordinary perturbation theories. However, these existing theories seem to be not so useful to clarify the aforementioned ARPES, since it spans the whole momentum region from the Fermi level (≡E<SUB>F</SUB> ) to the bottom of the valence band. According to recent experimental results, it has become clear that the ARPES evolve quite drastically as the momentum changes from E<SUB>F</SUB> to the band bottom. This spectral evolution appears quite universal for a wide varieties of eph systems, especially the intermediately coupled metallic ones. However, its origin seems beyond the conventional approximation theories mentioned above. Thus, the problem how eph interaction dominates the spectral shape has now emerged as a new challenge for the theory of solid state physics. <br /> In this work, we present a new pathintegral theory to calculate the ARPES of e=ph coupled systems. Our main purpose of this paper is to clarify the impact of eph interaction on the lineshape of ARPES. we consider a manyelectron system coupled with Einstein phonons, which is often called Holstein model. This model has been studied extensivery, with various interests ranging from the competition between metallic, CDW and SC phases, to the energy gap opening, by perturbative and nonperturbative methods. In our numerical calculation, the pathintegral is performed by the quantum Monte Carlo (QMC) simulation. Thus it is completely free from any other approximations. Give the QMC data of imaginary time Green's function, we reproduce the spectral function by the analytic continuation. By this means, we systematically study the spectral properties of the eph coupled systems based on the onedimensional and twodimensional (2D) Holstein models under various conditions. We find the band structure is greatly modified by the multiple scattering effect of electron with phonons, even if the whole system is still metallic and the eph coupling strength is intermediate. Around the band bottom, the spectrum takes a broad Gaussian, indicating the electron in this state is nearly localized and incoherent. While near the E<SUB>F</SUB>, the spectral shape is characterized by an asymmetric twoheaded Lorentzian, which means the electron in this state is almost coherent with a plane wave nature, extending over all the crystal. There are also dimensionality effects on the phonon peaks, which make them most clearly observed in the 2D nonhalffilled cases with no CDW gap. Our results qualitatively agree with recent experiments of high resolution ARPES on Be (0001) surface and Bi<SUB>2</SUB>Sr<SUB>2</SUB>CaCu<SUB>2</SUB>O<SUB>8</SUB>.  
所蔵  
値  有 