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

从统一的角度对铁电相变和超导相变进行了理论研究，并讨论了高相变温度的来源（T_f, T_c）。首先，在铁电体和反铁电体的混合晶体中，提出了一种核磁共振- nqr谱模型来确定相变点。接下来，为了解释一维（1D）氢键铁电体的相变，考虑到主晶格对质子构型的作用，建立了一个簇理论。结果表明，较高的T_f与质子-质子关系的大各向异性和主晶格向质子体系的重整化有关。在此基础上，给出了包含各种氢键铁电体键长信息的T_f的一般方程。讨论了产生高T_f的机理是X维（X=0,1,2,3）物质所共有的。基于上述理论结果，给出了准一维电子系统中CDW链中质子诱导有序点T_p的方程。讨论了卤素桥接混合价过渡金属配合物中CDW （T_p）与超导性（T_c）的竞争。链间氢键上的轻质子运动以与一维电子系统强耦合的形式引入。预测质子调节电子-电子相互作用，电子-质子耦合产生强烈的吸引力，导致超导态超越CDW态。最后，在碱掺杂富勒烯中，我利用本征大涨落，提出了具有较高T_c的声子介导超导模型。在相似的条件下，可以得到高T_c和高T_f (T_p)，这是一个有趣的结果。

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.