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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 Superconductor Insulator Transition ： ウィキペディア英語版 Superconductor Insulator Transition The Superconductor Insulator Transition is an example of a quantum phase transition, whereupon tuning some parameter in the Hamiltonian, a dramatic change in the behavior of the electrons occurs. The nature of how this transition occurs is disputed, and many studies seek to understand how the order parameter, $\backslash Psi\; =\backslash Delta\; \backslash exp(i\backslash theta)$, changes. Here $\backslash Delta$ is the amplitude of the order parameter, and $\backslash theta$ is the phase. Most theories involve either the destruction of the amplitude of the order parameter - by a reduction in the density of states at the Fermi surface, or by destruction of the phase coherence; which results from the proliferation of vortices. ==Destruction of superconductivity== In two dimensions, the subject of superconductivity becomes very interesting because the existence of true long-range order is not possible. How then is superconductivity obtained? In the 70's, Kosterlitz and Thouless (along with Berezinski) showed that a different kind of long-range order could exist - topological order - which showed power law correlations (meaning that by measuring the two-point correlation function $\backslash langle\backslash Psi(0)\backslash Psi(r)\backslash rangle\backslash propto\; r^$ it decays algebraically). This picture changes if disorder is included. Kosterlitz-Thouless behavior can be obtained, but the fluctuations of the order parameter are greatly enhanced, and the transition temperature is suppressed. The model to keep in mind in the understanding of how superconductivity occurs in a two-dimensional disordered superconductor is the following. At high temperatures, the system is in the normal state. As the system is cooled towards its transition temperature, superconducting grains begin to fluctuate in and out of existence. When one of these grains "pops" into existence, it is accelerated without dissipation for a time $\backslash tau$ before decaying back into the normal state. This has the effect of increasing the conductivity even before the system has condensed into the superconducting state. This increased conductivity above $T\_$ is referred to as paraconductivity, or fluctuation conductivity, and was first correctly described by Aslamazov and Larkin. As the system is cooled further, the lifetime of these fluctuations increase, and becomes comparable to the Ginzburg-Landau time $\backslash tau\_=\backslash frac$. Eventually, the amplitude $\backslash Delta$ of the order parameter becomes well defined (it is non-zero wherever there are superconducting patches), and it can begin to support phase fluctuations. These phase fluctuations set in at a lower temperature, and are caused by vortices - which are topological defects in the order parameter. It is the motion of vortices that gives rise to inflation of resistance below $T\_$. Eventually the system is cooled further, below the Kosterlitz-Thouless temperature $T\_$, all of the free vortices become bound into vortex-antivortex pairs, and the systems attains a state with zero resistance. 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「Superconductor Insulator Transition」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.