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Unified Theoretical Approach on High-Tc Superconducting and Ferroelectric Phase Transitions

高温超导和铁电相变的统一理论方法

基本信息

批准号：
04640364
负责人：
MATSUSHITA Eiko
金额：
$ 1.22万
依托单位：
GIFU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1994
项目状态：
已结题

项目摘要

Ferroelectric and superconducting transitions are studied theoretically from a unified picture for various phase transitions, and the origin of high transition temperature is discussed (T_f, T_c) . First, in the mixed crystals of ferro-and antiferro-electrics, and a model of NMR-NQR spectra is proposed to define the phase transition points. Next, to explain the phase transition in one-dimensional (1D) hydrogen-bonded ferroelectrics, a cluster theory is developed by taking into account the role of host lattice on the proton configurations. It is shown that rather high T_f is related with the large anisotropy among proton-proton correlations and the renormalization of the host lattice into the proton system. Furthermore, the general equation for T_f is presented including the information of bond lengths for various hydrogen-bonded ferroelectrics. It is discussed that the mechanism to produce high T_f is common to X-dimensional (X=0,1,2,3) substances. Basing on the above-mentioned theoretical results, the equation for T_p is presented as the proton-induced ordering point among CDW chains in quasi-1D electron systems. The competition between CDW (T_p) and superconductivity(T_c) is discussed in halogen-bridged mixed-valence transition-metal complexes. The light proton motion on the interchain hydrogen bonds is introduced in a strongly coupled form with the 1D-electron system. It is predicted that protons modulate the electron-electron interaction, and that the electron-proton coupling induces a strong attraction to lead the superconductivity surpassing the CDW state. Finally, in alkali-doped fullerene, I propose a model of phonon-mediated superconductivity with rather high T_c by making use of the intrinsic large fluctuation. It is the interesting result that both high T_c and high T_f (T_p) are obtained under the similar condition.

本文从统一的相变图象出发，对铁电和超导相变进行了理论研究，并讨论了高相变温度（T_f，T_c）的原因。首先，在铁电体和反铁电体的混晶中，提出了一种NMR-NQR谱模型来确定相变点。其次，为了解释一维氢键铁电体中的相变，考虑到主晶格对质子构型的作用，发展了一个团簇理论。结果表明，较高的T_f值与质子-质子关联的各向异性以及主晶格重整化为质子系统有关。此外，还给出了包含各种氢键铁电体键长信息的T_f通用方程。讨论了X维（X= 0，1，2，3）物质产生高T_f的共同机制。在上述理论结果的基础上，给出了准一维电子系统中质子诱导CDW链间有序点T_p的表达式。本文讨论了卤素桥联混合价过渡金属配合物中CDW（T_p）与超导电性（T_c）之间的竞争。轻质子在链间氢键上的运动以与一维电子系统强耦合的形式引入。预测质子调制电子-电子相互作用，电子-质子耦合引起强吸引，导致超导电性超过CDW态。最后，在碱金属掺杂的富勒烯中，利用声子的本征大涨落，提出了一个具有较高T_c的声子介导超导模型。有趣的是，在相同的条件下得到了高T_c和高T_f（T_p）。