WEKO3
アイテム
Dual Electron-phonon Coupling Model for Giant Photoenhancements of Dielectric Constant and Electronic Conductivity in SrTiO3
https://ir.soken.ac.jp/records/674
https://ir.soken.ac.jp/records/674dc97c1de-530f-44c9-8655-fdb938456caf
名前 / ファイル | ライセンス | アクション |
---|---|---|
要旨・審査要旨 (265.9 kB)
|
||
本文 (4.9 MB)
|
Item type | 学位論文 / Thesis or Dissertation(1) | |||||
---|---|---|---|---|---|---|
公開日 | 2010-02-22 | |||||
タイトル | ||||||
タイトル | Dual Electron-phonon Coupling Model for Giant Photoenhancements of Dielectric Constant and Electronic Conductivity in SrTiO3 | |||||
タイトル | ||||||
タイトル | Dual Electron-phonon Coupling Model for Giant Photoenhancements of Dielectric Constant and Electronic Conductivity in SrTiO3 | |||||
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 |
邱, 宇
× 邱, 宇 |
|||||
フリガナ |
クイユ
× クイユ |
|||||
著者 |
QIU, Yu
× QIU, Yu |
|||||
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989号 | |||||
研究科 | ||||||
値 | 高エネルギー加速器科学研究科 | |||||
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 | 2006-09-29 | |||||
学位授与年度 | ||||||
値 | 2006 | |||||
要旨 | ||||||
内容記述タイプ | Other | |||||
内容記述 | Since some 3D type perovkite compounds have been found in the experiments to<br />give gigantic dielectric constant, in contrast to the ordinary dielectrics, its<br />underlying microscopic mechanism has attractted much attention in the field of<br />solid state theory. As is well-known, the ferroelectric modes play an important roll<br />in the dielectric property, transportation and phase transition or these materials.<br />Many efforts were already performed on the connection of this ferroelectric mode<br />with the quartic or sextic anharmonic oscillators. ln experiment, glgantic<br />photo-enhancements of the electronic conductivity and the dielectric constant have<br />recently been observed in SrTiO3. lt was also pointed out that, this dielectric<br />enhancement remains to exist only under the ultraviolet (UV) illumination, while<br />vanishes as the illumination is turned off. As for the photo-induced electronic<br />conduction in SrTiO<sub>3</sub>, it is expected to be an alternative mechanism from that of the<br />ordinary field induced one in metallic systems. However, the microscopic origin of<br />these photo-induced phenomena has not yet been clarified theoretically. Thus, this<br />is just the motivation of the present study.<br /> We will give a short introduction to the soft mode theory in the<br />second chapter since our work will be mainly based on this theory.<br />The spatial structure and the electronic property of this 3D<br />perovskite. SrTi0<sub>3</sub>, are also stated. since we will focus our efforts<br />only on this compound in the present work. Some key points of the<br />previous studies on the fundamental properties of SrTiO<sub>3</sub>, are<br />summerized as well. =n Chapter 3, a detailed illustration is given<br />to the Super-Para-Electric (SPE) large polarons, from the set-up of<br />the cheoretic model to the numerical calculatlons, and ends up with<br />the impurity effect on this polaron. Combining the experimentally<br />observed dielectrlc and conductive properties with previous<br />theoretical researches on the model for this crystal, we give a further<br />investigation into the model and come up with a new model for the<br />photo excited state of the crystal. By which, we can adiabatically<br />obtain the corresponding energy surface and find all the metastable<br />states on it. With the investigation of each of such states, We can<br />find its connection with the dielectric and conductive property of<br />this crystal・ We also give an investigation into the most stable<br />quasiparticle state for the many electron system within the adeabatic<br />method and give a description to the possible lattice configurations<br />for the photo excited state of the electron and phonon coupling system.<br />Then it is followed by Chapter 4, the appllcations of this SPE polaron<br />theory in the interpretation of the photo-induced giant dielectric<br />constant and electronic conductivity. We will first discuss one of<br />the fundamental problems for phonons, phonon softening or phonon<br />hardening with the introduction of e-p coupling. Then we will apply<br />our SPE large polaron theory to the experimentally observed static<br />dielectric enhancement in srTiO<sub>3</sub>, clarifying the microscopic origin <br />of this photo-induced phase transition. In the following, we will<br />give a phenomenological interpretation to the experimentally reported<br />metallic conduction in SrTiO<sub>3</sub> by studying the translational property<br />of the polarons. In Chapter 5, we will discuss the relaxation process<br />of the lattice after the photo-excitation. It has already been studied<br />that for polymers, the formation of the polaron or exciton is an<br />ultra-fast process. <sup>[6l]</sup> In experiment, these states could be detected<br />and predicted from the spectra. However, by virtue of the molecular<br />dynamics theory, the information of the lattice configuration as well<br />as the electronic state can be traced so as to compare with the<br />energetic evolution. Then, the lattice relaxation process could be<br />recognized more clearly. We will first give a deschption to the <br />molecular dynamics theory for the e-p interacting system. Then, we<br />will apply this method to SrTiO<sub>3</sub> and give some detailed descriptions<br />about the relaxation process in this crystal. We will show the<br />formation of the SPE large polaron is an ultra-fast process of about<br />several picoseconds, and how the electron and phonon interaction<br />system releases its energy so as to reach its new stable state. The<br />influence of the electron and phonon interaction strength and the<br />size of the electron and phonon coupling system on the relaxation<br />process will be shown. A summary of all the conclusions of these<br />studies is given at Chapter 6. | |||||
所蔵 | ||||||
値 | 有 |