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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Charge ordering ： ウィキペディア英語版 Charge ordering Charge ordering (CO) is a (first- or second-order) phase transition occurring mostly in strongly correlated materials such as transition metal oxides or organic conductors. Due to the strong interaction between electrons, charges are localized on different sites leading to a disproportionation and an ordered superlattice. It appears in different patterns ranging from vertical to horizontal stripes to a checkerboard–like pattern, and it is not limited to the two-dimensional case. The charge order transition is accompanied by symmetry breaking and may lead to ferroelectricity. It is often found in close proximity to superconductivity and colossal magnetoresistance. This long range order phenomena was first discovered in magnetite (Fe3O4) by Verwey in 1939. He observed an increase of the electrical resistivity by two orders of magnitude at TCO=120K, suggesting a phase transition which is now well known as the Verwey transition. He was the first to propose the idea of an ordering process in this context. The charge ordered structure of magnetite was solved in 2011 by a group led by Paul Attfield with the results published in ''Nature''. == Theoretical description == The extended one-dimensional Hubbard model delivers a good description of the charge order transition with the on-site and nearest neighbor Coulomb repulsion U and V. It emerged that V is a crucial parameter and important for developing the charge order state. Further model calculations try to take the temperature and an interchain interaction into account. The extended Hubbard model for a single chain including inter-site and on-site interaction V and U as well as the parameter $\backslash delta\_d$ for a small dimerization which can be typically found in the (TMTTF)2X compounds is presented as follows: $H\; =\; -t\; \backslash sum\_\; \backslash sum\_\; \backslash left\; (\; \backslash left\; (1+\; \backslash left(-1\; \backslash right)^i\; \backslash delta\_d\; \backslash right)c^\_c\_+\; h.c\; \backslash right)+\; U\; \backslash sum\_i\; n\_n\_\; +\; V\; \backslash sum\_n\_i,\; n\_$ where t describes the transfer integral or the kinetic energy of the electron and $c^\_$ and $c\_$ are the creation and annihilation operator, respectively, for an electron with the spin $\backslash sigma\; =\; \backslash uparrow\; ,\; \backslash downarrow$ at the $i$th or $i+1$th site. $n\_$ denotes the density operator. For non-dimerized systems, $\backslash delta\_d$ can be set to zero Normally, the on-site Coulomb repulsion U stays unchanged only t and V can vary with pressure. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Charge ordering」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.